--- /dev/null
+@Article{Abreu2003:fl_albumin,
+ author = {Magda S C Abreu and Lu\'is M B B Estronca and Maria Jo{\~{a}}o Moreno
+ and Winchil L C Vaz},
+ title = {Binding of a fluorescent lipid amphiphile to albumin and its
+ transfer to lipid bilayer membranes},
+ journal = {Biophys J},
+ year = {2003},
+ volume = {84},
+ number = {1},
+ pages = {386--99},
+ month = {Jan},
+ abstract = {Kinetics and thermodynamics of the binding of a fluorescent
+ lipid amphiphile, Rhodamine Green(TM)-tetradecylamide
+ (RG-C(14:0)), to bovine serum albumin were characterized in
+ an equilibrium titration and by stopped-flow fluorimetry.
+ The binding equilibrium of RG-C(14:0) to albumin was then
+ used to reduce its concentration in the aqueous phase to a
+ value below its critical micelle concentration. Under these
+ conditions, the only two species of RG-C(14:0) in the
+ system were the monomer in aqueous solution in equilibrium
+ with the protein-bound species. After previous
+ determination of the kinetic and thermodynamic parameters
+ for association of RG-C(14:0) with albumin, the kinetics of
+ insertion of the amphiphile into and desorption off lipid
+ bilayer membranes in different phases (solid,
+ liquid-ordered, and liquid-disordered phases, presented as
+ large unilamellar vesicles) were studied by stopped-flow
+ fluorimetry at 30 degrees C. Insertion and desorption rate
+ constants for association of the RG-C(14:0) monomer with
+ the lipid bilayers were used to obtain lipid/water
+ equilibrium partition coefficients for this fluorescent
+ amphiphile. The direct measurement of these partition
+ coefficients is shown to provide a new method for the
+ indirect determination of the equilibrium partition
+ coefficient of similar molecules between two defined lipid
+ phases if they coexist in the same membrane.},
+ pmid = {12524292},
+ doi = {10.1016/S0006-3495(03)74859-0},
+}
+@Article{Abreu2004:kinetics_ld_lo,
+ author = {Magda S C Abreu and Maria Jo{\~{a}}o Moreno and Winchil L C Vaz},
+ title = {Kinetics and thermodynamics of association of a phospholipid
+ derivative with lipid bilayers in liquid-disordered and
+ liquid-ordered phases},
+ journal = {Biophys J},
+ year = {2004},
+ volume = {87},
+ number = {1},
+ pages = {353--65},
+ month = {Jul},
+ abstract = {We have measured the rates of insertion into, desorption
+ from, and spontaneous interlayer translocation (flip-flop)
+ in liquid-disordered and liquid-ordered phase lipid bilayer
+ membranes, of the fluorescent phospholipid derivative
+ NBD-dimyristoylphosphatidyl ethanolamine. This study made
+ use of a recently described method that exploits a detailed
+ knowledge of the binding kinetics of an amphiphile to
+ bovine serum albumin, to recover the insertion and
+ desorption rate constants when the albumin-bound amphiphile
+ is transferred through the aqueous phase to the membrane
+ and vice versa. The lipid bilayers, studied as large
+ unilamellar vesicles, were prepared from pure
+ 1-palmitoyl-2-oleoylphosphatidylcholine in the
+ liquid-disordered phase; and from two
+ cholesterol-containing binary lipid mixtures,
+ 1-palmitoyl-2-oleoylphosphatidylcholine and cholesterol
+ (molar ratio of 1:1), and egg sphingomyelin and cholesterol
+ (molar ratio of 6:4), both in the liquid-ordered phase.
+ Insertion, desorption, and translocation rate constants and
+ equilibrium constants for association of the amphiphile
+ monomer with the lipid bilayers were directly measured
+ between 15 degrees and 35 degrees C, and the standard free
+ energies, enthalpies, and entropies, as well as the
+ activation energies for these processes, were derived from
+ this data. The equilibrium partition coefficients for
+ partitioning of the amphiphile between the aqueous phase
+ and the different membrane phases were also derived, and
+ permitted the estimation of hypothetical partition
+ coefficients and the respective energetic parameters for
+ partitioning between the different lipid phases if these
+ were to coexist in the same membrane.},
+ pmid = {15240470},
+ doi = {10.1529/biophysj.104.040576},
+}
+@Book{Arrhenius1908:world_in_making,
+ author = {Svante Arrhenius},
+ title = {Worlds in the making; the evolution of the universe},
+ publisher = {New York, London, Harper},
+ year = 1908,
+ address = {http://www.archive.org/details/worldsinmakingev00arrhrich}
+}
+
+@Article{Bachmann1992:autocatalysis_micelles,
+ author = {Pascale Angelica Bachmann and Pier Luigi Luisi and Jacques Lang},
+ title = {Autocatalytic self-replicating micelles as models for prebiotic structures},
+ journal = {Nature},
+ year = 1992,
+ volume = 357,
+ pages = {57--9},
+ month = {May},
+ abstract = {MICELLES that can catalyse their replication have been
+ described recently1–3. In the previous experiments,
+ micelles (or bilayer vesicles4) were always present
+ in the initial reaction mixture—that is, the system
+ was presented with the bounded structures required
+ for autocatalysis. Here we describe a system in
+ which autocatalytic micelles are formed from
+ amphiphiles that are themselves generated from a
+ hydrolysis reaction in the absence of compartmental
+ structures. Alkaline hydrolysis of ethyl caprylate
+ (itself insoluble in water) yields sodium caprylate,
+ initially at a very slow rate; but as soon as
+ sufficient caprylate is formed for aggregation into
+ micelles to take place, there is an exponential
+ increase in reaction rate owing to micellar
+ catalysis. These self-assembling surfactant
+ structures may consequently provide a model system
+ for studies of prebiotic chemistry. The possible
+ relevance of this process to prebiotic chemistry is
+ emphasized by our observation that the micelles can
+ be converted into more-robust vesicles by a pH
+ change induced by dissolved CO2.},
+ doi = {10.1038/357057a0}
+}
+@Article{Bai1997:lipid_movementbodipy,
+ author = {J Bai and R E Pagano},
+ title = {Measurement of spontaneous transfer and transbilayer movement
+ of BODIPY-labeled lipids in lipid vesicles},
+ journal = {Biochemistry},
+ year = {1997},
+ volume = {36},
+ number = {29},
+ pages = {8840--8},
+ month = {Jul},
+ abstract = {An assay was developed to study the spontaneous transfer
+ and transbilayer movement (flip-flop) of lipid analogs
+ labeled with the fluorescent fatty acid, 5-(5,7-dimethyl
+ BODIPY)-1-pentanoic acid (C5-DMB-) in large unilamellar
+ lipid vesicles comprised of 1-palmitoyl-2-oleoyl
+ phosphatidylcholine (POPC). The assay is based on the
+ concentration-dependent changes in fluorescence intensity
+ that occur when donor vesicles containing a C5-DMB-lipid
+ are mixed with nonfluorescent acceptor vesicles. A kinetic
+ model was developed to describe the time-dependent changes
+ in concentration of a lipid undergoing both spontaneous
+ transfer between unilamellar vesicles and transbilayer
+ movement within the vesicle membranes, and a mathematical
+ solution was obtained. Data were obtained using
+ C5-DMB-labeled analogs of sphingomyelin (C5-DMB-SM),
+ ceramide (C5-DMB-Cer), phosphatidylcholine (C5-DMB-PC), and
+ diacylglycerol (C5-DMB-DAG), and kinetic parameters for
+ each lipid were determined using a nonlinear least-squares
+ fitting program. The half-times for interbilayer transfer
+ of the lipids were C5-DMB-SM (21 s) < C5-DMB-PC (350 s)
+ approximately C5-DMB-Cer (400 s) << C5-DMB-DAG (100 h).
+ C5-DMB-Cer (t1/2 approximately 22 min) and C5-DMB-DAG (t1/2
+ approximately 70 ms) exhibited rapid spontaneous
+ transbilayer movement, while C5-DMB-SM (t1/2 approximately
+ 3.3 h) and C5-DMB-PC (t1/2 approximately 7.5 h) moved
+ across the bilayer very slowly. These results provide a
+ basis for interpreting the behavior of these lipid analogs
+ in cells.},
+ pmid = {9220970},
+ doi = {10.1021/bi970145r},
+}
+@Article{Baron2004:sm_raft_composition,
+ author = {Carl B Baron and Ronald F Coburn},
+ title = {Smooth muscle raft-like membranes},
+ journal = {J Lipid Res},
+ year = {2004},
+ volume = {45},
+ number = {1},
+ pages = {41--53},
+ month = {Jan},
+ abstract = {We developed a method for extracting raft-like,
+ liquid-ordered membranes from the particulate fraction
+ prepared from porcine trachealis smooth muscle. This
+ fraction, which contains most of the plasma membrane in
+ this tissue, was homogenized in the presence of cold 0.5\%
+ Triton X-100. After centrifugation, membranes containing
+ high contents of sphingomyelin (SM) and cholesterol and low
+ phosphatidylcholine (PC) contents remained in the pellet.
+ Thirty-five millimolar octyl glucoside (OG) extracted 75\%
+ of these membranes from the Triton X-100-resistant pellet.
+ These membranes had low buoyant densities and accounted for
+ 28\% of the particulate fraction lipid. Their lipid
+ composition, 22\% SM, 60\% cholesterol, 11\%
+ phosphatidylethanolamine, 8\% PC, <1\%
+ phosphatidylinositol, and coisolation with 5'-nucleotidase
+ and caveolin-1 suggest that they are liquid-ordered
+ membranes. We compared characteristics of OG and Triton
+ X-100 extractions of the particulate fraction. In contrast
+ to Triton X-100 extractions, membranes released from the
+ particulate fraction by OG were mainly collected in low
+ buoyant fractions at densities ranging from 1.05 to 1.11
+ g/ml and had phospholipid and cholesterol contents
+ consistent with a mixture of liquid-ordered and
+ liquid-disordered membranes. Thus, OG extraction of
+ apparent liquid-ordered membranes from Triton
+ X-100-resistant pellets was not due to selective extraction
+ of these membranes. Low buoyant density appears not to be
+ unique for liquid-ordered membranes.},
+ pmid = {14563832},
+ doi = {10.1194/jlr.M300402-JLR200},
+}
+@Article{Baumgart2003:curvature_and_line_tension,
+ author = {Tobias Baumgart and Samuel T Hess and Watt W Webb},
+ title = {Imaging coexisting fluid domains in biomembrane models
+ coupling curvature and line tension},
+ journal = {Nature},
+ year = {2003},
+ volume = {425},
+ number = {6960},
+ pages = {821--4},
+ month = {Oct},
+ abstract = {Lipid bilayer membranes--ubiquitous in biological systems
+ and closely associated with cell function--exhibit rich
+ shape-transition behaviour, including bud formation and
+ vesicle fission. Membranes formed from multiple lipid
+ components can laterally separate into coexisting liquid
+ phases, or domains, with distinct compositions. This
+ process, which may resemble raft formation in cell
+ membranes, has been directly observed in giant unilamellar
+ vesicles. Detailed theoretical frameworks link the
+ elasticity of domains and their boundary properties to the
+ shape adopted by membranes and the formation of particular
+ domain patterns, but it has been difficult to
+ experimentally probe and validate these theories. Here we
+ show that high-resolution fluorescence imaging using two
+ dyes preferentially labelling different fluid phases
+ directly provides a correlation between domain composition
+ and local membrane curvature. Using freely suspended
+ membranes of giant unilamellar vesicles, we are able to
+ optically resolve curvature and line tension interactions
+ of circular, stripe and ring domains. We observe long-range
+ domain ordering in the form of locally parallel stripes and
+ hexagonal arrays of circular domains, curvature-dependent
+ domain sorting, and membrane fission into separate vesicles
+ at domain boundaries. By analysing our observations using
+ available membrane theory, we are able to provide
+ experimental estimates of boundary tension between fluid
+ bilayer domains.},
+ pmid = {14574408},
+ doi = {10.1038/nature02013},
+}
+@Article{Budin2010:ool_review,
+ author = {Itay Budin and Jack W Szostak},
+ title = {Expanding roles for diverse physical phenomena during the
+ origin of life},
+ journal = {Annu Rev Biophys},
+ year = {2010},
+ volume = {39},
+ number = {},
+ pages = {245--63},
+ month = {Jun},
+ abstract = {Recent synthetic approaches to understanding the origin of
+ life have yielded insights into plausible pathways for the
+ emergence of the first cells. Here we review current
+ experiments with implications for the origin of life,
+ emphasizing the ability of unexpected physical processes to
+ facilitate the self-assembly and self-replication of the
+ first biological systems. These laboratory efforts have
+ uncovered novel physical mechanisms for the emergence of
+ homochirality; the concentration and purification of
+ prebiotic building blocks; and the ability of the first
+ cells to assemble, grow, divide, and acquire greater
+ complexity. In the absence of evolved biochemical
+ capabilities, such physical processes likely played an
+ essential role in early biology.},
+ pmid = {20192779},
+ doi = {10.1146/annurev.biophys.050708.133753},
+}
+@Article{Cascales1996:mds_dpps_area,
+ author = {J. J. L\'opez Cascales and H. J. C. Berendsen and J. Garc\'ia de la Torre},
+ title = {Molecular Dynamics Simulation of Water between Two Charged Layers of Dipalmitoylphosphatidylserine},
+ journal = {J. Phys. Chem.},
+ year = 1996,
+ volume = 100,
+ number = 21,
+ pages = {8621--7},
+ month = {May},
+ abstract = {A molecular dynamics simulation of water between two
+ charged layers of dipalmitoylphosphatidylserine in
+ its liquid-crystalline state with atomic detail was
+ carried out. From an analysis of a trajectory of 184
+ ps of length, we obtained information about the
+ dynamics and structure of water between such charged
+ layers. The most remarkable conclusions of this work
+ indicate that the presence of counterions and charge
+ interactions between adjacent phospholipids produce
+ a screening of the electric field which reduces the
+ strength of the lipid-water interactions. In this
+ way, only minor differences of the behavior of the
+ water compared to uncharged phospholipids were
+ found. This conclusion was based on the calculation
+ of the following properties: electric potential and
+ water dipole orientation across the water layer,
+ radial distribution function of water about lipid
+ atoms, and diffusion and orientational relaxation
+ time of water. },
+ doi = {10.1021/jp9516405}
+}
+@Article{Chen2004:competition_model_protocells,
+ author = {Irene A Chen and Richard W Roberts and Jack W Szostak},
+ title = {The emergence of competition between model protocells},
+ journal = {Science},
+ year = {2004},
+ volume = {305},
+ number = {5689},
+ pages = {1474--6},
+ month = {Sep},
+ abstract = {The transition from independent molecular entities to
+ cellular structures with integrated behaviors was a crucial
+ aspect of the origin of life. We show that simple physical
+ principles can mediate a coordinated interaction between
+ genome and compartment boundary, independent of any genomic
+ functions beyond self-replication. RNA, encapsulated in
+ fatty acid vesicles, exerts an osmotic pressure on the
+ vesicle membrane that drives the uptake of additional
+ membrane components, leading to membrane growth at the
+ expense of relaxed vesicles, which shrink. Thus, more
+ efficient RNA replication could cause faster cell growth,
+ leading to the emergence of Darwinian evolution at the
+ cellular level.},
+ pmid = {15353806},
+ doi = {10.1126/science.1100757},
+}
+@Article{Copley2007:rna_world,
+ author = {Shelley D Copley and Eric Smith and Harold J Morowitz},
+ title = {The origin of the RNA world: co-evolution of genes and
+ metabolism},
+ journal = {Bioorg Chem},
+ year = {2007},
+ volume = {35},
+ number = {6},
+ pages = {430--43},
+ month = {Dec},
+ abstract = {Discoveries demonstrating that RNA can serve genetic,
+ catalytic, structural, and regulatory roles have provided
+ strong support for the existence of an RNA World that
+ preceded the origin of life as we know it. Despite the
+ appeal of this idea, it has been difficult to explain how
+ macromolecular RNAs emerged from small molecules available
+ on the early Earth. We propose here a mechanism by which
+ mutual catalysis in a pre-biotic network initiated a
+ progression of stages characterized by ever larger and more
+ effective catalysts supporting a proto-metabolic network,
+ and the emergence of RNA as the dominant macromolecule due
+ to its ability to both catalyze chemical reactions and to
+ be copied in a template-directed manner. This model
+ suggests that many features of modern life, including the
+ biosynthetic pathways leading to simple metabolites, the
+ structures of organic and metal ion cofactors,
+ homochirality, and template-directed replication of nucleic
+ acids, arose long before the RNA World and were retained as
+ pre-biotic systems became more sophisticated.},
+ pmid = {17897696},
+ doi = {10.1016/j.bioorg.2007.08.001},
+}
+@Article{Deamer1986:aphiphile_origin,
+ author = {D W Deamer},
+ title = {Role of amphiphilic compounds in the evolution of membrane
+ structure on the early earth},
+ journal = {Orig Life Evol Biosph},
+ year = {1986},
+ volume = {17},
+ number = {1},
+ pages = {3--25},
+ abstract = {A variety of amphiphilic compounds have the capacity to
+ self-assemble into membranous structures in the form of
+ bilayers. The earliest cellular organisms must have
+ incorporated such compounds into boundary membranes, and
+ this review discusses amphiphilic components of the
+ prebiotic environment which would be candidates. One
+ possible source is organic material carried to the earth's
+ surface by meteoritic infall. To test this, we have
+ extracted and analysed non-polar substances from the
+ Murchison carbonaceous chondrite, and found that at least
+ some of the components can produce boundary structures
+ which resemble membranes. This observation suggests that
+ membranous boundary structures were present on the early
+ earth, and available to participate in the origin and
+ evolution of the first cellular forms of life.},
+ pmid = {3796965},
+}
+@Article{Deamer1989:murchison_chondrite,
+ author = {D W Deamer and R M Pashley},
+ title = {Amphiphilic components of the Murchison carbonaceous
+ chondrite: surface properties and membrane formation},
+ journal = {Orig Life Evol Biosph},
+ year = {1989},
+ volume = {19},
+ number = {1},
+ pages = {21--38},
+ abstract = {We have investigated physicochemical properties of
+ amphiphilic compounds in carbonaceous meteorites. The
+ primary aim was to determine whether such materials
+ represent plausible sources of lipid-like compounds that
+ could have been involved as membrane components in
+ primitive cells. Samples of the Murchison CM2 chondrite
+ were extracted with chloroform-methanol, and the
+ chloroform-soluble material was separated by
+ two-dimensional thin layer chromatography. Fluorescence,
+ iodine stains and charring were used to identify major
+ components on the plates. These were then scraped and
+ eluted as specific fractions which were investigated by
+ fluorescence and absorption spectra, surface chemical
+ methods, gas chromatography-mass spectrometry, and electron
+ microscopy. Fraction 5 was strongly fluorescent, and
+ contained pyrene and fluoranthene, the major polycyclic
+ aromatic hydrocarbons of the Murchison chondrite. This
+ fraction was also present in extracts from the Murray and
+ Mighei CM2 chondrites. Fraction 3 was surface active,
+ forming apparent monomolecular films at air-water
+ interfaces. Surface force measurements suggested that
+ fraction 3 contained acidic groups. Fraction 1 was also
+ surface active, and certain components could self-assemble
+ into membranous vesicles which encapsulated polar solutes.
+ The observations reported here demonstrate that organic
+ compounds plausibly available on the primitive Earth
+ through meteoritic infall are surface active, and have the
+ ability to self-assemble into membranes.},
+ pmid = {2748144},
+}
+@Article{Deamer1991:amphiphile_origin,
+ author = {D Deamer and S I Kuzina and A I Mikhailov and E I Maslikova
+ and S A Seleznev},
+ title = {Origin of amphiphilic molecules and their role in primary
+ structure formation},
+ journal = {J Evol Biochem Physiol},
+ year = {1991},
+ volume = {27},
+ number = {3},
+ pages = {212--7},
+ month = {May-Jun},
+ abstract = {Attempts to solve two fundamental questions are described:
+ the first concerns which mechanisms were responsible for
+ the self-assembly of membrane structures on the prebiotic
+ Earth, and the second concerns the routes by which
+ considerable amounts of membrane amphiphiles formed from
+ simpler hydrocarbons. The physicochemical properties of
+ several amphiphilic compounds extracted from the Murchison
+ carbonaceous chondrite were studied, using infra-red and
+ fluorescent spectroscopy, measurements of surface activity,
+ chromato-mass spectrometry, and polarization and electron
+ microscopy. The results supported previous observations
+ that amphiphilic and aromatic hydrocarbons were present in
+ significant quantities, and the first demonstration of
+ surface activity among a number of acidic derivatives of
+ hydrocarbons is reported. In addition, one fraction of the
+ surface-active compounds can form bilayer structures,
+ showing that membranes could have self-assembled on the
+ prebiotic Earth. Photochemical oxidation of hydrocarbons
+ is shown to be a likely source of the amphiphilic molecules
+ required for the self-assembly of primary membrane
+ structures.},
+ pmid = {11538377},
+}
+@Article{Demel1987:ps_area,
+ author = {R A Demel and F Paltauf and H Hauser},
+ title = {Monolayer characteristics and thermal behavior of natural and
+ synthetic phosphatidylserines},
+ journal = {Biochemistry},
+ year = {1987},
+ volume = {26},
+ number = {26},
+ pages = {8659--65},
+ month = {Dec},
+ abstract = {The monolayer properties and thermal behavior of different
+ phosphatidylserines are presented. At neutral pH and 22
+ degrees C, saturated phosphatidylserines form condensed
+ monolayers while unsaturated phosphatidylserines form
+ liquid-expanded films. Under similar conditions,
+ dimyristoylphosphatidylserine undergoes a transition from
+ the liquid-expanded to the condensed state. At pH 4 and 22
+ degrees C, the surface pressure-area isotherms are shifted
+ to smaller areas relative to the monolayers recorded at
+ neutral pH. The condensation observed at pH 4 is close to
+ that produced at pH 7.4 by the addition of 10 mM CaCl2. As
+ regards the molecular packing in monolayers and the thermal
+ behavior, 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine
+ (DPPS) and its ether analogue are similar, albeit not
+ identical. Below 30 mN/m, monolayers of the ether analogue
+ are even more condensed than those of DPPS. The
+ order-disorder transition of the ether analogue occurs
+ usually at higher temperatures than that of the diacyl
+ compound. Sonicated phosphatidylserine dispersions
+ consisting of small unilamellar vesicles show anomalous
+ thermal properties compared to sonicated
+ phosphatidylcholine dispersions. They exhibit sharp
+ order-disorder transitions at similar or even slightly
+ elevated temperatures compared to unsonicated
+ phosphatidylserine dispersions. This anomaly is explained
+ in terms of a pH gradient across the bilayer membrane of
+ the small unilamellar phosphatidylserine vesicle. The
+ internal surface pH is more acidic than the external pH,
+ leading to some protonation of phosphatidylserine
+ molecules. This in turn leads to a condensation of
+ phosphatidylserine molecules on the inner bilayer surface.
+ Such a gradient is proposed to be responsible for the
+ thermodynamic stability of highly curved negatively charged
+ bilayer vesicles.},
+ pmid = {3442681},
+}
+@Article{Dworkin2001:amphiphile_assembly,
+ author = {J Dworkin and D Deamer and S Sandford and L Allamandola},
+ title = {Self-assembling amphiphilic molecules: Synthesis in simulated
+ interstellar/precometary ices},
+ journal = {Proc Natl Acad Sci U S A},
+ year = {2001},
+ volume = {98},
+ number = {3},
+ pages = {815--9},
+ month = {Jan},
+ abstract = {Interstellar gas and dust constitute the primary material
+ from which the solar system formed. Near the end of the hot
+ early phase of star and planet formation, volatile, less
+ refractory materials were transported into the inner solar
+ system as comets and interplanetary dust particles. Once
+ the inner planets had sufficiently cooled, late
+ accretionary infall seeded them with complex organic
+ compounds [Oró, J. (1961) Nature (London) 190, 389-390;
+ Delsemme, A. H. (1984) Origins Life 14, 51-60; Anders, E.
+ (1989) Nature (London) 342, 255-257; Chyba, C. F. & Sagan,
+ C. (1992) Nature (London) 355, 125-131]. Delivery of such
+ extraterrestrial compounds may have contributed to the
+ organic inventory necessary for the origin of life.
+ Interstellar ices, the building blocks of comets, tie up a
+ large fraction of the biogenic elements available in
+ molecular clouds. In our efforts to understand their
+ synthesis, chemical composition, and physical properties,
+ we report here that a complex mixture of molecules is
+ produced by UV photolysis of realistic, interstellar ice
+ analogs, and that some of the components have properties
+ relevant to the origin of life, including the ability to
+ self-assemble into vesicular structures.},
+ pmid = {11158552},
+ doi = {10.1073/pnas.98.3.815},
+}
+@Article{Estronca2007:dhe_kinetics,
+ author = {Lu\'is M B B Estronca and Maria Jo{\~{a}}o Moreno and Winchil L C
+ Vaz},
+ title = {Kinetics and thermodynamics of the association of
+ dehydroergosterol with lipid bilayer membranes},
+ journal = {Biophys J},
+ year = {2007},
+ volume = {93},
+ number = {12},
+ pages = {4244--53},
+ month = {Dec},
+ abstract = {We have examined the detailed kinetics and thermodynamics
+ of the association of Ergosta-5,7,9(11),22-tetraen-3beta-ol
+ (dehydroergosterol, DHE) with lipid bilayers prepared from
+ 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), a 1:1
+ binary mixture of POPC and cholesterol (Chol), and a 6:4
+ binary mixture of egg sphingomyelin (SpM) and Chol.
+ Association of DHE with all three membranes was shown to be
+ entropically driven, most so in the case of SpM-Chol
+ bilayers. Equilibrium partition coefficients for
+ partitioning of DHE between the lipid phase and the aqueous
+ phase were shown to be similar for POPC and POPC-Chol
+ bilayers between 15 and 35 degrees C. Partitioning into the
+ SpM-Chol bilayer is favored at higher temperatures and
+ there is a crossover in solubility preference at
+ approximately 25 degrees C. Insertion (k(+)) and desorption
+ (k(-)) rate constants were shown to be very similar for
+ POPC and POPC-Chol bilayer membranes, but were lower for
+ SpM-Chol bilayers. Similar results were previously reported
+ by us for the association of other amphiphiles with these
+ membranes. We propose a model for the microscopic structure
+ of a POPC-Chol (1:1) bilayer membrane that is consistent
+ with these observations.},
+ pmid = {17766353},
+ doi = {10.1529/biophysj.107.112847},
+}
+@Article{Ferris1987:prebiotic_synthesis,
+ author = {J P Ferris},
+ title = {Prebiotic synthesis: problems and challenges},
+ journal = {Cold Spring Harb Symp Quant Biol},
+ year = {1987},
+ volume = {52},
+ pages = {29--35},
+ pmid = {2456880},
+}
+@Article{Gaus2005:macrophage_lipid_distribution,
+ author = {Katharina Gaus and Macarena Rodriguez and Kalani R Ruberu and
+ Ingrid Gelissen and Timothy M Sloane and Leonard Kritharides
+ and Wendy Jessup},
+ title = {Domain-specific lipid distribution in macrophage plasma
+ membranes},
+ journal = {J. Lipid Res.},
+ year = {2005},
+ volume = {46},
+ number = {7},
+ pages = {1526--38},
+ month = {Jul},
+ abstract = {Lipid rafts, defined as cholesterol- and sphingolipid-rich
+ domains, provide specialized lipid environments understood
+ to regulate the organization and function of many plasma
+ membrane proteins. Growing evidence of their existence,
+ protein cargo, and regulation is based largely on the study
+ of isolated lipid rafts; however, the consistency and
+ validity of common isolation methods is controversial.
+ Here, we provide a detailed and direct comparison of the
+ lipid and protein composition of plasma membrane "rafts"
+ prepared from human macrophages by different methods,
+ including several detergent-based isolations and a
+ detergent-free method. We find that detergent-based and
+ detergent-free methods can generate raft fractions with
+ similar lipid contents and a biophysical structure close to
+ that previously found on living cells, even in cells not
+ expressing caveolin-1, such as primary human macrophages.
+ However, important differences between isolation methods
+ are demonstrated. Triton X-100-resistant rafts are less
+ sensitive to cholesterol or sphingomyelin depletion than
+ those prepared by detergent-free methods. Moreover, we show
+ that detergent-based methods can scramble membrane lipids
+ during the isolation process, reorganizing lipids
+ previously in sonication-derived nonraft domains to
+ generate new detergent-resistant rafts. The role of rafts
+ in regulating the biological activities of macrophage
+ plasma membrane proteins may require careful reevaluation
+ using multiple isolation procedures, analyses of lipids,
+ and microscopic techniques.},
+ pmid = {15863834},
+ doi = {10.1194/jlr.M500103-JLR200},
+}
+@Article{Hanczyc2003:protocell_model,
+ author = {Martin M Hanczyc and Shelly M Fujikawa and Jack W Szostak},
+ title = {Experimental models of primitive cellular compartments:
+ encapsulation, growth, and division},
+ journal = {Science},
+ year = {2003},
+ volume = {302},
+ number = {5645},
+ pages = {618--22},
+ month = {Oct},
+ abstract = {The clay montmorillonite is known to catalyze the
+ polymerization of RNA from activated ribonucleotides. Here
+ we report that montmorillonite accelerates the spontaneous
+ conversion of fatty acid micelles into vesicles. Clay
+ particles often become encapsulated in these vesicles, thus
+ providing a pathway for the prebiotic encapsulation of
+ catalytically active surfaces within membrane vesicles. In
+ addition, RNA adsorbed to clay can be encapsulated within
+ vesicles. Once formed, such vesicles can grow by
+ incorporating fatty acid supplied as micelles and can
+ divide without dilution of their contents by extrusion
+ through small pores. These processes mediate vesicle
+ replication through cycles of growth and division. The
+ formation, growth, and division of the earliest cells may
+ have occurred in response to similar interactions with
+ mineral particles and inputs of material and energy.},
+ pmid = {14576428},
+ doi = {10.1126/science.1089904},
+}
+@Article{Hargreaves1977:pl_synthesis,
+ author = {W R Hargreaves and S J Mulvihill and D W Deamer},
+ title = {Synthesis of phospholipids and membranes in prebiotic
+ conditions},
+ journal = {Nature},
+ year = {1977},
+ volume = {266},
+ number = {5597},
+ pages = {78--80},
+ month = {Mar},
+ pmid = {840303},
+}
+@Article{Hargreaves1978:liposome_from_aphiphiles,
+ author = {W R Hargreaves and D W Deamer},
+ title = {Liposomes from ionic, single-chain amphiphiles},
+ journal = {Biochemistry},
+ year = {1978},
+ volume = {17},
+ number = {18},
+ pages = {3759--68},
+ month = {Sep},
+ abstract = {In studies of the minimum physiochemical requirements for
+ lipid membrane formation, we have made liposomes from
+ dilute, aqueous dispersions of C(8)-C(18) single-chain
+ amphiphiles. In general, membrane formation from ionic
+ soaps and detergents requires the presence of uncharged
+ amphiphiles. Vesicles were characterized by phase-contrast
+ microscopy, by trapping of ionic dyes, as well as by
+ negativestain and freez-frature electron microscopy. They
+ were typically heterogeneous in size, but the average
+ diameter could be experimentally varied in some cases over
+ the range of 1 to 100 micrometer. Uni-, oligo-, and
+ multilamellar vesicles were observed. Membrane permeability
+ to various solutes was determined in part by a new
+ technique which utilized phase-contract microscopy; when
+ impermeable vesciles exclude added solutes such as sucrose,
+ refractive index differences are created between vesicle
+ contents and surrounding medium, so that the vesicles
+ appear bright in the phase microscope. Permeant solutes do
+ not produce this effect. Spectrophotometric permeability
+ determinations confirmed the results of this technique and
+ provided quantitative measures of permeability. Monoalkyl
+ liposomes have potential uses as models of biomembranes and
+ in drug delivery. They are also relevant to the prebiotic
+ origin of biomembranes.},
+ pmid = {698196},
+}
+@Article{Huang1999:chol_solubility_model,
+ author = {J Huang and G W Feigenson},
+ title = {A microscopic interaction model of maximum solubility of
+ cholesterol in lipid bilayers},
+ journal = {Biophys. J},
+ year = {1999},
+ volume = {76},
+ number = {4},
+ pages = {2142--57},
+ month = {Apr},
+ abstract = {We recently reported the equilibrium maximum solubility of
+ cholesterol in a lipid bilayer, chi*chol, to be 0.66 in
+ four different phosphatidylcholines, and 0.51 in a
+ phosphatidylethanolamine (Huang, J.,J.T. Buboltz, and G. W.
+ Feigenson. 1999. Biochim. Biophys. Acta. in press). Here we
+ present a model of cholesterol-phospholipid mixing that
+ explains these observed values of chi*chol. Monte Carlo
+ simulations show that pairwise-additivity of
+ nearest-neighbor interactions is inadequate to describe all
+ the chi*chol values. Instead, if cholesterol multibody
+ interactions are assigned highly unfavorable energy, then
+ jumps occur in cholesterol chemical potential that lead to
+ its precipitation from the bilayer. Cholesterol
+ precipitation is most likely to occur near three discrete
+ values of cholesterol mole fraction, 0.50, 0.57, and 0.67,
+ which correspond to cholesterol/phospholipid mole ratios of
+ 1/1, 4/3, and 2/1, respectively. At these solubility
+ limits, where cholesterol chemical potential jumps, the
+ cholesterol-phospholipid bilayer mixture forms highly
+ regular lipid distributions in order to minimize
+ cholesterol-cholesterol contacts. This treatment shows that
+ dramatic structural and thermodynamic changes can occur at
+ particular cholesterol mole fractions without any
+ stoichiometric complex formation. The physical origin of
+ the unfavorable cholesterol multibody interaction is
+ explained by an "umbrella model": in a bilayer, nonpolar
+ cholesterol relies on polar phospholipid headgroup coverage
+ to avoid the unfavorable free energy of cholesterol contact
+ with water. Thus, at high cholesterol mole fraction, this
+ unfavorable free energy, not any favorable
+ cholesterol-phospholipid interaction, dominates the mixing
+ behavior. This physical origin also explains the
+ "cholesterol condensing effect" and the increase in acyl
+ chain order parameter in cholesterol-phospholipid
+ mixtures.},
+ pmid = {10096908},
+}
+@Article{Huang1999:cholesterol_solubility,
+ author = {J Huang and J T Buboltz and G W Feigenson},
+ title = {Maximum solubility of cholesterol in phosphatidylcholine and
+ phosphatidylethanolamine bilayers},
+ year = {1999},
+ volume = {1417},
+ number = {1},
+ journal = {Biochim. Biophys. Acta},
+ pages = {89--100},
+ month = {Feb},
+ abstract = {In any lipid bilayer membrane, there is an upper limit on
+ the cholesterol concentration that can be accommodated
+ within the bilayer structure; excess cholesterol will
+ precipitate as crystals of pure cholesterol monohydrate.
+ This cholesterol solubility limit is a well-defined
+ quantity. It is a first-order phase boundary in the
+ phospholipid/cholesterol phase diagram. There are many
+ different solubility limits in the literature, but no clear
+ picture has emerged that can unify the disparate results.
+ We have studied the effects that different sample
+ preparation methods can have on the apparent experimental
+ solubility limit. We find that artifactual demixing of
+ cholesterol can occur during conventional sample
+ preparation and that this demixed cholesterol may produce
+ artifactual cholesterol crystals. Therefore,
+ phospholipid/cholesterol suspensions which are prepared by
+ conventional methods may manifest variable, falsely low
+ cholesterol solubility limits. We have developed two novel
+ preparative methods which are specifically designed to
+ prevent demixing during sample preparation. For detection
+ of the cholesterol crystals, X-ray diffraction has proven
+ to be quantitative and highly sensitive. Experiments based
+ on these methods yield reproducible and precise cholesterol
+ solubility limits: 66 mol\% for phosphatidylcholine (PC)
+ bilayers and 51 mol\% for phosphatidylethanolamine (PE)
+ bilayers. We present evidence that these are true,
+ equilibrium values. In contrast to the dramatic headgroup
+ effect (PC vs. PE), acyl chain variations had no effect on
+ the cholesterol solubility limit in four different
+ PC/cholesterol mixtures.},
+ pmid = {10076038},
+}
+@Article{Inger2009:gard_mutations,
+ author = {Aron Inger and Ariel Solomon and Barak Shenhav and Tsviya
+ Olender and Doron Lancet},
+ title = {Mutations and lethality in simulated prebiotic networks},
+ journal = {J Mol Evol},
+ year = {2009},
+ volume = {69},
+ number = {5},
+ pages = {568--78},
+ month = {Nov},
+ abstract = {The Graded Autocatalysis Replication Domain (GARD) model
+ describes an origin of life scenario which involves
+ non-covalent compositional assemblies, made of monomeric
+ mutually catalytic molecules. GARD constitutes an
+ alternative to informational biopolymers as a mechanism of
+ primordial inheritance. In the present work, we examined
+ the effect of mutations, one of the most fundamental
+ mechanisms for evolution, in the context of the networks of
+ mutual interaction within GARD prebiotic assemblies. We
+ performed a systematic analysis analogous to single and
+ double gene deletions within GARD. While most deletions
+ have only a small effect on both growth rate and molecular
+ composition of the assemblies, $\approx$10\% of the deletions
+ caused lethality, or sometimes showed enhanced fitness.
+ Analysis of 14 different network properties on 2,000
+ different GARD networks indicated that lethality usually
+ takes place when the deleted node has a high molecular
+ count, or when it is a catalyst for such node. A
+ correlation was also found between lethality and node
+ degree centrality, similar to what is seen in real
+ biological networks. Addressing double knockout mutations,
+ our results demonstrate the occurrence of both synthetic
+ lethality and extragenic suppression within GARD networks,
+ and convey an attempt to correlate synthetic lethality to
+ network node-pair properties. The analyses presented help
+ establish GARD as a workable alternative prebiotic
+ scenario, suggesting that life may have begun with large
+ molecular networks of low fidelity, that later underwent
+ evolutionary compaction and fidelity augmentation.},
+ pmid = {19787385},
+ doi = {10.1007/s00239-009-9281-y},
+}
+@Article{Israelachvili1975:amphiphile_self_assembly,
+ author = {Jacob N Israelachvili and D John Mitchell and Barry W Ninham},
+ title = {Theory of Self-Assembly of Hydrocarbon Amphiphiles
+ into Micelles and Bilayers},
+ journal = {J. Chem. Soc., Faraday Trans. 2,},
+ year = 1976,
+ volume = 72,
+ pages = 1525,
+ abstract = {A simple theory is developed that accounts for many of
+ the observed physical properties of micelles, both
+ globular and rod-like, and of bilayer vesicles
+ composed of ionic or zwitterionic amphiphiles. The
+ main point of departure from previous theories lies
+ in the recognition and elucidation of the role of
+ geometric constraints in self-assembly. The linking
+ together of thermodynamics, interaction free
+ energies and geometry results in a general framework
+ which permits extension to more complicated
+ self-assembly problems.},
+ doi = {10.1039/F29767201525}
+}
+
+@Article{Janas2004:rna_membrane_transporter,
+ author = {Teresa Janas and Tadeusz Janas and Michael Yarus},
+ title = {A membrane transporter for tryptophan composed of RNA},
+ journal = {RNA},
+ year = {2004},
+ volume = {10},
+ number = {10},
+ pages = {1541--9},
+ month = {Oct},
+ abstract = {We have incorporated an RNA binding site for the biological
+ amino acid tryptophan within an RNA complex with affinity
+ for phospholipid bilayer membranes. The resulting RNA
+ (9:10Trp) creates a selective route through the bilayer for
+ the amino acid. Binding and enhanced tryptophan
+ permeability are nonlinear in RNA concentration, suggesting
+ that RNA aggregation is required for both. Tryptophan
+ permeability saturates with increased concentration, though
+ at approximately 1000-fold greater level than when binding
+ a free aptamer. The RNA (9:10Trp) complex, bound at a mean
+ of two per liposome, halves the activation energy for
+ tryptophan transport (to 46 kJ/mole), specifically
+ increasing tryptophan entry to a maximal velocity of 0.5
+ sec(-1) per liposome with little or no accompanying
+ increase in general permeability. Individual RNAs turn over
+ tens of thousands of times at high tryptophan
+ concentration. Thus, a specific passive membrane
+ transporter whose properties overlap those of
+ single-molecule transporter proteins, can be made of RNA
+ alone. Permeability changes probably rely on disturbances
+ in lipid conformation as well as on an advantageous low
+ free energy position for tryptophan at the membrane. Other
+ RNA activities may yield other RNA-membrane nanosystems via
+ this route.},
+ pmid = {15383677},
+ doi = {10.1261/rna.7112704},
+}
+@Article{Jones1990:lipid_transfer,
+ author = {J D Jones and T E Thompson},
+ title = {Mechanism of spontaneous, concentration-dependent phospholipid
+ transfer between bilayers},
+ journal = {Biochemistry},
+ year = {1990},
+ volume = {29},
+ number = {6},
+ pages = {1593--600},
+ month = {Feb},
+ abstract = {We have previously demonstrated that spontaneous
+ phospholipid transfer between bilayer vesicles at higher
+ vesicle concentrations is characterized not only by a
+ first-order desorption rate but also by a second-order
+ process dependent on vesicle concentration (Jones &
+ Thompson, 1989b). We have extended our studies to examine
+ the mechanism of this second-order process by investigating
+ transfer as a function of lipid type, temperature, aqueous
+ medium composition, and vesicle size. The results suggest a
+ mechanism of concentration-dependent transfer in which the
+ rate of lipid monomer desorption from vesicle bilayers is
+ enhanced in transient vesicle-vesicle complexes.},
+ pmid = {2334718},
+}
+@Article{Joyce2002:rna_world,
+ author = {Gerald F Joyce},
+ title = {The antiquity of RNA-based evolution},
+ journal = {Nature},
+ year = {2002},
+ volume = {418},
+ number = {6894},
+ pages = {214--21},
+ month = {Jul},
+ abstract = {All life that is known to exist on Earth today and all life
+ for which there is evidence in the geological record seems
+ to be of the same form--one based on DNA genomes and
+ protein enzymes. Yet there are strong reasons to conclude
+ that DNA- and protein-based life was preceded by a simpler
+ life form based primarily on RNA. This earlier era is
+ referred to as the 'RNA world', during which the genetic
+ information resided in the sequence of RNA molecules and
+ the phenotype derived from the catalytic properties of
+ RNA.},
+ pmid = {12110897},
+ doi = {10.1038/418214a},
+}
+@Article{Kafri2010:enantiomer_gard,
+ author = {Ran Kafri and Omer Markovitch and Doron Lancet},
+ title = {Spontaneous chiral symmetry breaking in early molecular
+ networks},
+ journal = {Biol Direct},
+ year = {2010},
+ volume = {5},
+ pages = {38},
+ pmid = {20507625},
+ doi = {10.1186/1745-6150-5-38},
+}
+@Article{Katz1988:pl_packing_chol,
+ author = {S Lund-Katz and H M Laboda and L R McLean and M C Phillips},
+ title = {Influence of molecular packing and phospholipid type on rates
+ of cholesterol exchange},
+ journal = {Biochemistry},
+ year = {1988},
+ volume = {27},
+ number = {9},
+ pages = {3416--23},
+ month = {May},
+ abstract = {The rates of [14C]cholesterol transfer from small
+ unilamellar vesicles containing cholesterol dissolved in
+ bilayers of different phospholipids have been determined to
+ examine the influence of phospholipid-cholesterol
+ interactions on the rate of cholesterol desorption from the
+ lipid-water interface. The phospholipids included
+ unsaturated phosphatidylcholines (PC's) (egg PC,
+ dioleoyl-PC, and soybean PC), saturated PC (dimyristoyl-PC
+ and dipalmitoyl-PC), and sphingomyelins (SM's) (egg SM,
+ bovine brain SM, and N-palmitoyl-SM). At 37 degrees C, for
+ vesicles containing 10 mol\% cholesterol, the half-times
+ for exchange are about 1, 13, and 80 h, respectively, for
+ unsaturated PC, saturated PC, and SM. In order to probe how
+ differences in molecular packing in the bilayers cause the
+ rate constants for cholesterol desorption to be in the
+ order unsaturated PC greater than saturated PC greater than
+ SM, nuclear magnetic resonance (NMR) and monolayer methods
+ were used to evaluate the cholesterol physical state and
+ interactions with phospholipid. The NMR relaxation
+ parameters for [4-13C]cholesterol reveal no differences in
+ molecular dynamics in the above bilayers. Surface pressure
+ (pi)-molecular area isotherms for mixed monolayers of
+ cholesterol and the above phospholipids reveal that SM
+ lateral packing density is greater than that of the PC with
+ the same acyl chain saturation and length (e.g., at pi = 5
+ mN/m, where both monolayers are in the same physical state,
+ dipalmitoyl-PC and palmitoyl-SM occupy 87 and 81
+ A2/molecule, respectively).(ABSTRACT TRUNCATED AT 250
+ WORDS)},
+ pmid = {3390441},
+}
+@Article{Kumar1991:lipid_packing,
+ author = {V V Kumar},
+ title = {Complementary molecular shapes and additivity of the packing
+ parameter of lipids},
+ journal = {Proc Natl Acad Sci U S A},
+ year = {1991},
+ volume = {88},
+ number = {2},
+ pages = {444--8},
+ month = {Jan},
+ abstract = {Physical dimensions of a membrane component influence its
+ phase preference upon hydration. A dimensionless packing
+ parameter, S, given by S = V/al, where V is the hydrocarbon
+ volume, a is the area of the head group, and l is the
+ critical length of the hydrocarbon chain, is useful in
+ determining the phase preference of a lipid, and the value
+ of S usually lies between 0.5 and 1 for bilayers. Here, the
+ value of S is calculated for phosphatidylcholine (PC) and
+ lysophosphatidylcholine (lysoPC) as a function of chain
+ length, and it is shown that diacylPC having an S value of
+ less than 0.74 does not form bilayers. For example,
+ diacylPC, up to a chain length of eight carbon atoms, forms
+ only micelles, whereas higher homologs with S greater than
+ 0.74 form bilayers. It is also shown that when lipid
+ molecules having complementary shapes associate, the value
+ of S becomes additive. Using the additivity of S, a number
+ of experimental results for lipid mixtures can be
+ explained. For example, lysoPC and cholesterol form
+ lamellar structures between 45 and approximately 80 mol\%
+ cholesterol, and the additive value of S for this region is
+ between 0.74 and 1. Similarly, the additivity of S shows
+ that the maximum amount of cholesterol that can be
+ incorporated into PC bilayers is 50 mol\%, in agreement
+ with experimental studies.},
+ pmid = {1988944},
+}
+@Article{Lange1983:chol_distribution,
+ author = {Y Lange and B V Ramos},
+ title = {Analysis of the distribution of cholesterol in the intact
+ cell},
+ journal = {J. Biol. Chem.},
+ year = {1983},
+ volume = {258},
+ number = {24},
+ pages = {15130--4},
+ month = {Dec},
+ abstract = {We have used the enzyme cholesterol oxidase, which
+ catalyzes the oxidation of cholesterol to
+ cholest-4-en-3-one, to examine the distribution of
+ cholesterol in cultured fibroblasts, Chinese hamster ovary
+ cells, and isolated rat liver hepatocytes. While the plasma
+ membrane normally was not attacked by cholesterol oxidase,
+ we found that treating cells with low ionic strength buffer
+ and glutaraldehyde rendered their cholesterol highly
+ susceptible to oxidation. Most of the cholesterol was
+ oxidized in all three cell types: 94\% in fibroblasts, 92\%
+ in Chinese hamster ovary cells, and 80\% in hepatocytes.
+ Given that the enzyme had access only to the outer surface
+ of the cells and cholesterol can move rapidly across the
+ fixed plasma membrane, these values are taken to reflect
+ the fraction of cellular cholesterol present in the plasma
+ membrane. Additional experiments confirmed this
+ interpretation. Fibroblasts were labeled with
+ [3H]cholesterol by brief exposure to exogenous radiolabel
+ and incubated with [14C]mevalonic acid to label cholesterol
+ biosynthetically. Cholesterol oxidase attacked at least
+ 97\% of the exogenous label but as little as 10\% of the
+ biosynthetically labeled cholesterol. These data suggest
+ that the cholesterol oxidase did not reach the
+ intracellular pool and that cholesterol in the plasma
+ membrane is not in rapid equilibrium with internal
+ membranes. A study of the transfer of cholesterol to plasma
+ from cells labeled biosynthetically with [3H]cholesterol
+ and exogenously with [14C]cholesterol confirmed the
+ different subcellular distribution of the two labels. These
+ studies demonstrate that an unexpectedly high proportion of
+ cell cholesterol is associated with plasma membranes and
+ that this cholesterol pool can be rapidly and selectively
+ labeled and oxidized. These features make cholesterol a
+ useful specific marker for the plasma membrane.},
+ pmid = {6418742},
+}
+@Article{Leirer2009:vesicle_fission,
+ author = {C Leirer and B Wunderlich and V M Myles and M F Schneider},
+ title = {Phase transition induced fission in lipid vesicles},
+ journal = {Biophys Chem},
+ year = {2009},
+ volume = {143},
+ number = {1-2},
+ pages = {106--9},
+ month = {Jul},
+ abstract = {In this work we demonstrate how the first order phase
+ transition in giant unilamellar vesicles (GUVs) can
+ function as a trigger for membrane fission. When driven
+ through their gel-fluid phase transition GUVs exhibit
+ budding or pearl formation. These buds remain connected to
+ the mother vesicle presumably by a small neck. Cooling
+ these vesicles from the fluid phase (T>T(m)) through the
+ phase transition into the gel state (T<T(m)), leads to
+ complete rupture and fission of the neck, while the mother
+ vesicle remains intact. Pearling tubes which formed upon
+ heating break-up and decay into multiple individual
+ vesicles which then diffuse freely. Finally we demonstrate
+ that mimicking the intracellular bulk viscosity by
+ increasing the bulk viscosity to 40 cP does not affect the
+ overall fission process, but leads to a significant
+ decrease in the size of the released vesicles.},
+ pmid = {19442430},
+ doi = {10.1016/j.bpc.2009.04.002},
+}
+@article{McConnell2003,
+ author = {Harden M McConnell and Arun Radhakrishnan},
+ title = {Condensed complexes of cholesterol and phospholipids},
+ journal = {Biochem. Biophys. Acta},
+ year = {2003},
+ volume = {1610},
+ number = {2},
+ pages = {159--73},
+ month = {Mar},
+ abstract = {There is overwhelming evidence that lipid bilayer regions
+ of animal cell membranes are in a liquid state.
+ Quantitative models of these bilayer regions must then be
+ models of liquids. These liquids are highly non-ideal. For
+ example, it has been known for more than 75 years that
+ mixtures of cholesterol and certain phospholipids undergo
+ an area contraction or condensation in lipid monolayers at
+ the air-water interface. In the past 3 years, a
+ thermodynamic model of "condensed complexes" has been
+ proposed to account for this non-ideal behavior. Here we
+ give an overview of the model, its relation to other
+ models, and to modern views of the properties of animal
+ cell membranes.},
+ pmid = {12648771}
+}
+@Article{McConnell2006,
+ author = {Harden McConnell and Arun Radhakrishnan},
+ title = {Theory of the deuterium NMR of sterol-phospholipid membranes},
+ journal = {Proc Natl Acad Sci U S A},
+ year = {2006},
+ volume = {103},
+ number = {5},
+ pages = {1184--1189},
+ month = {Jan},
+ abstract = {A general theoretical model is described for the NMR
+ spectra of mixtures of sterols and deuterium-labeled
+ phospholipids. In the case of homogeneous membranes, the
+ average quadrupole splittings are determined by equilibria
+ between lipids in cholesterol-phospholipid complexes and
+ lipids not in complexes. Chemical exchange of lipids
+ between those in the free state and those in the complex
+ state affects the deuterium resonance line shapes. The
+ lifetime of a phospholipid molecule in an
+ ergosterol-dipalmitoylphosphatidylcholine complex is
+ estimated to be of the order of 10(-5) s on the basis of
+ the observed line broadenings. In the vicinity of a
+ critical point of a cholesterol-phospholipid mixture,
+ fluctuations in the concentration of complexes also can
+ contribute to the deuterium nuclear resonance line
+ broadening. At the critical point, the temperature
+ derivative of the concentration of complexes is
+ discontinuous. There is a corresponding jump in the
+ calculated heat capacity as well as in the temperature
+ derivative of the deuterium NMR first moment.},
+ pmid = {16432189},
+ doi = {10.1073/pnas.0510514103},
+}
+@Article{Nichols1982:ret_amphiphile_transfer,
+ author = {J W Nichols and R E Pagano},
+ title = {Use of resonance energy transfer to study the kinetics of
+ amphiphile transfer between vesicles},
+ journal = {Biochemistry},
+ year = {1982},
+ volume = {21},
+ number = {8},
+ pages = {1720--6},
+ month = {Apr},
+ pmid = {7082641},
+}
+@Article{Nichols1985:phospholipid_monomer_vesicle_thermodynamics,
+ author = {J W Nichols},
+ title = {Thermodynamics and kinetics of phospholipid monomer-vesicle
+ interaction},
+ journal = {Biochemistry},
+ year = {1985},
+ volume = {24},
+ number = {23},
+ pages = {6390--8},
+ month = {Nov},
+ abstract = {Resonance energy transfer between acyl chain labeled
+ (7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylcholine
+ (NBD-PC) and head group labeled (lissamine rhodamine B
+ sulfonyl)phosphatidylethanolamine (N-Rh-PE) was used to
+ monitor the rate of NBD-PC transfer between two populations
+ of dioleoylphosphatidylcholine (DOPC) vesicles.
+ Equilibration of NBD-PC between DOPC vesicles occurs by the
+ diffusion of soluble monomers through the water phase,
+ which is a first-order process. Conditions were used such
+ that the apparent transfer rate constant is equal to the
+ rate constant for monomer-vesicle dissociation into
+ solution. The partition distribution of NBD-PC between DOPC
+ vesicles and water was determined by measuring the loss of
+ NBD-PC from vesicles into solution following the dilution
+ of small amounts of vesicles in buffer. The acyl chain
+ length and temperature dependence of both the rate and
+ partition measurements were determined, and a free energy
+ diagram for NBD-PC-soluble monomer-vesicle interactions was
+ constructed. The conclusions of this analysis are the
+ following: NBD-PC dissociation from and association with
+ the bilayer require passage through a high-energy
+ transition state resulting predominantly from enthalpic
+ energy. The activation energy for NBD-PC-vesicle
+ dissociation becomes more positive and the standard free
+ energy of NBD-PC transfer from water to vesicles becomes
+ more negative with increasing acyl chain length. The
+ standard free energy of transfer for NBD-PC from water to
+ vesicles results predominantly from differences in enthalpy
+ between the membrane and water phases. The enthalpy of
+ activation for association increases with acyl chain length
+ and is larger than expected for an aqueous
+ diffusion-limited process in bulk water.},
+ pmid = {4084528},
+}
+@Book{Oparin1938:origin_of_life,
+ author = {Aleksandr Ivanovich Oparin},
+ translator = {Sergius Morgulis},
+ title = {The origin of life},
+ publisher = {Macmillan, New York},
+ year = 1938,
+ href = {http://ucr.worldcat.org/title/origin-of-life/oclc/958765}}
+@Article{Pandit2002:mds_dpps,
+ author = {Sagar A Pandit and Max L Berkowitz},
+ title = {Molecular dynamics simulation of dipalmitoylphosphatidylserine
+ bilayer with Na+ counterions},
+ journal = {Biophys J},
+ year = {2002},
+ volume = {82},
+ number = {4},
+ pages = {1818--27},
+ month = {Apr},
+ abstract = {We performed a molecular dynamics simulation of
+ dipalmitoylphosphatidylserine (DPPS) bilayer with Na+
+ counterions. We found that hydrogen bonding between the NH
+ group and the phosphate group leads to a reduction in the
+ area per headgroup when compared to the area in
+ dipalmitoylphosphatidylcholine bilayer. The Na+ ions bind
+ to the oxygen in the carboxyl group of serine, thus giving
+ rise to a dipolar bilayer similar to
+ dipalmitoylphosphatidylethanolamine bilayer. The results of
+ the simulation show that counterions play a crucial role in
+ determining the structural and electrostatic properties of
+ DPPS bilayer.},
+ pmid = {11916841},
+ doi = {10.1016/S0006-3495(02)75532-X},
+}
+@Article{Pankov2005:chol_distribution,
+ author = {Roumen Pankov and Tania Markovska and Rusina Hazarosova and
+ Peter Antonov and Lidia Ivanova and Albena Momchilova},
+ title = {Cholesterol distribution in plasma membranes of $\betaup$1
+ integrin-expressing and $\betaup$1 integrin-deficient fibroblasts},
+ journal = {Archives of biochemistry and biophysics},
+ year = {2005},
+ volume = {442},
+ number = {2},
+ pages = {160--8},
+ month = {Oct},
+ abstract = {The effect of integrin receptors on the level and
+ transmembrane localization of cholesterol molecules was
+ investigated in beta1 integrin-expressing (beta1) and beta1
+ integrin-deficient (beta1 null) cells. We found that the
+ content of specific raft components-cholesterol,
+ sphingomyelin, and caveolin-was increased in
+ integrin-expressing cells. Integrin presence affected as
+ well the transmembrane distribution of cholesterol-a higher
+ percent was found in the plasma membrane outer monolayer of
+ beta1 compared to beta1 null cells. Sphingomyelin depletion
+ reduced the presence of cholesterol in the outer membrane
+ monolayer of both cell lines, but the differences in
+ cholesterol asymmetry, observed between beta1 and beta1
+ null cells before sphingomyelinase treatment were
+ preserved. These findings implied that integrin receptors
+ affected the non-random transmembrane distribution of
+ cholesterol. Finally, a higher percent of
+ detergent-resistant membranes was obtained from beta1
+ integrin-expressing cells, suggesting that the presence of
+ these receptors in the membranes influenced the formation
+ and/or stabilization of lipid raft domains.},
+ pmid = {16165083},
+}
+@Article{Pike2002:lipid_raft_composition,
+ author = {Linda J Pike and Xianlin Han and Koong-Nah Chung and Richard
+ W Gross},
+ title = {Lipid rafts are enriched in arachidonic acid and
+ plasmenylethanolamine and their composition is independent of
+ caveolin-1 expression: a quantitative electrospray
+ ionization/mass spectrometric analysis.},
+ journal = {Biochemistry},
+ year = 2002,
+ volume = 41,
+ number = 6,
+ pages = {2075--88},
+ month = Feb,
+ abstract = {Lipid rafts are specialized cholesterol-enriched membrane
+ domains that participate in cellular signaling processes.
+ Caveolae are related domains that become invaginated due to
+ the presence of the structural protein, caveolin-1. In this
+ paper, we use electrospray ionization mass spectrometry
+ (ESI/MS) to quantitatively compare the phospholipids
+ present in plasma membranes and nondetergent lipid rafts
+ from caveolin-1-expressing and nonexpressing cells. Lipid
+ rafts are enriched in cholesterol and sphingomyelin as
+ compared to the plasma membrane fraction. Expression of
+ caveolin-1 increases the amount of cholesterol recovered in
+ the lipid raft fraction but does not affect the relative
+ proportions of the various phospholipid classes.
+ Surprisingly, ESI/MS demonstrated that lipid rafts are
+ enriched in plasmenylethanolamines, particularly those
+ containing arachidonic acid. While the total content of
+ anionic phospholipids was similar in plasma membranes and
+ nondetergent lipid rafts, the latter were highly enriched
+ in phosphatidylserine but relatively depleted in
+ phosphatidylinositol. Detergent-resistant membranes made
+ from the same cells showed a higher cholesterol content
+ than nondetergent lipid rafts but were depleted in anionic
+ phospholipids. In addition, these detergent-resistant
+ membranes were not enriched in arachidonic acid-containing
+ ethanolamine plasmalogens. These data provide insight into
+ the structure of lipid rafts and identify potential new
+ roles for these domains in signal transduction.},
+ pmid = 11827555,
+ mlid = 21685765,
+}
+ @Manual{R:maincite,
+ title = {R: A Language and Environment for Statistical
+ Computing},
+ author = {R Development Core Team},
+ organization = {R Foundation for Statistical Computing},
+ address = {Vienna, Austria},
+ year = 2011,
+ note = {{ISBN} 3-900051-07-0},
+ url = {http://www.R-project.org}
+ }
+@Article{Rao1982:pc_synthesis,
+ author = {M Rao and M R Eichberg and J Or\'o},
+ title = {Synthesis of phosphatidylcholine under possible primitive
+ earth conditions},
+ journal = {J Mol Evol},
+ year = {1982},
+ volume = {18},
+ number = {3},
+ pages = {196--202},
+ abstract = {Using a primitive Earth evaporating pond model, the
+ synthesis of phosphatidylcholine was accomplished when a
+ reaction mixture of choline chloride and disodium
+ phosphatidate, in the presence of cyanamide and traces of
+ acid, was evaporated and heated at temperatures ranging
+ from 25 degrees to 100 degrees C for 7 hours. Optimum
+ yields of about 15\% were obtained at 80 degrees C.
+ Phosphatidylcholine was identified by chromatographic,
+ chemical and enzymatic degradation methods. On enzymatic
+ hydrolysis with phospholipase A2 and phospholipase C,
+ lysophosphatidylcholine and phosphorylcholine were formed,
+ respectively. Alkaline hydrolysis gave
+ glycerophosphorylcholine. The synthesis of
+ phosphatidylcholine as the major compound was accompanied
+ by the formation of lysophosphatidylcholine in smaller
+ amounts. Cyanamide was found to be essential for the
+ formation of phosphatidylcholine, and only traces of HCl,
+ of the order of that required to convert the disodium
+ phosphatidate to free phosphatidic acid were found
+ necessary for the synthesis. This work suggests that
+ phosphatidylcholine, which is an essential component of
+ most biological membranes, could have been synthesized on
+ the primitive Earth.},
+ pmid = {7097779},
+}
+
+@Book{Rasmussen2008:protocells,
+ editor = {Steen Rasmussen and Mark A. Bedau and Liaohai Chen and David Deamer and David C. Krakauer and Norman H. Packard and Peter F. Stadler},
+ title = {Protocells: Bridging Nonliving and Living Matter},
+ publisher = {The MIT Press},
+ year = 2008,
+ edition = 1}
+@Article{Robinson1995:mds_chol_area,
+ author = {A J Robinson and W G Richards and P J Thomas and M M Hann},
+ title = {Behavior of cholesterol and its effect on head group and chain
+ conformations in lipid bilayers: a molecular dynamics study},
+ journal = {Biophys J},
+ year = {1995},
+ volume = {68},
+ number = {1},
+ pages = {164--70},
+ month = {Jan},
+ abstract = {Cholesterol molecules were put into a computer-modeled
+ hydrated bilayer of dimyristoyl phosphatidyl choline
+ molecules, and molecular dynamics simulations were run to
+ characterize the effect of this important molecule on
+ membrane structure and dynamics. The effect was judged by
+ observing differences in order parameters, tilt angles, and
+ the fraction of gauche bonds along the hydrocarbon chains
+ between lipids adjacent to cholesterol molecules and
+ comparing them with those further away. It was observed
+ that cholesterol causes an increase in the fraction of
+ trans dihedrals and motional ordering of chains close to
+ the rigid steroid ring system with a decrease in the kink
+ population. The hydrogen-bonding interactions between
+ cholesterol and lipid molecules were determined from radial
+ distribution calculations and showed the cholesterol
+ hydroxyl groups either solvated by water, or forming
+ hydrogen bond contacts with the oxygens of lipid carbonyl
+ and phosphate groups. The dynamics and conformation of the
+ cholesterol molecules were investigated and it was seen
+ that they had a smaller tilt with respect to the bilayer
+ normal than the lipid chains and furthermore that the
+ hydrocarbon tail of the cholesterol was conformationally
+ flexible.},
+ pmid = {7711238},
+ doi = {10.1016/S0006-3495(95)80171-2},
+}
+@article{Rousseeuw1987:silhouettes,
+ title = "Silhouettes: A graphical aid to the interpretation
+ and validation of cluster analysis",
+ journal = "Journal of Computational and Applied Mathematics",
+ volume = 20,
+ pages = "53 - 65",
+ year = 1987,
+ issn = "0377-0427",
+ doi = "10.1016/0377-0427(87)90125-7",
+ url =
+ "http://www.sciencedirect.com/science/article/B6TYH-45GN65V-6/2/18986ecfab1157f7f05da39a3b08ea73",
+ author = "Peter J. Rousseeuw",
+ keywords = "Graphical display",
+ keywords = "cluster analysis",
+ keywords = "clustering validity",
+ keywords = "classification",
+ abstract = "A new graphical display is proposed for partitioning
+ techniques. Each cluster is represented by a
+ so-called silhouette, which is based on the
+ comparison of its tightness and separation. This
+ silhouette shows which objects lie well within their
+ cluster, and which ones are merely somewhere in
+ between clusters. The entire clustering is displayed
+ by combining the silhouettes into a single plot,
+ allowing an appreciation of the relative quality of
+ the clusters and an overview of the data
+ configuration. The average silhouette width provides
+ an evaluation of clustering validity, and might be
+ used to select an [`]appropriate' number of
+ clusters."
+}
+@Article{Segre2000:agard,
+ author = {D Segr\'e and D Ben-Eli and D Lancet},
+ title = {Compositional genomes: prebiotic information transfer in
+ mutually catalytic noncovalent assemblies},
+ journal = {Proc Natl Acad Sci U S A},
+ year = {2000},
+ volume = {97},
+ number = {8},
+ pages = {4112--7},
+ month = {Apr},
+ abstract = {Mutually catalytic sets of simple organic molecules have
+ been suggested to be capable of self-replication and
+ rudimentary chemical evolution. Previous models for the
+ behavior of such sets have analyzed the global properties
+ of short biopolymer ensembles by using graph theory and a
+ mean field approach. In parallel, experimental studies with
+ the autocatalytic formation of amphiphilic assemblies
+ (e.g., lipid vesicles or micelles) demonstrated
+ self-replication properties resembling those of living
+ cells. Combining these approaches, we analyze here the
+ kinetic behavior of small heterogeneous assemblies of
+ spontaneously aggregating molecules, of the type that could
+ form readily under prebiotic conditions. A statistical
+ formalism for mutual rate enhancement is used to
+ numerically simulate the detailed chemical kinetics within
+ such assemblies. We demonstrate that a straightforward set
+ of assumptions about kinetically enhanced recruitment of
+ simple amphiphilic molecules, as well as about the
+ spontaneous growth and splitting of assemblies, results in
+ a complex population behavior. The assemblies manifest a
+ significant degree of homeostasis, resembling the
+ previously predicted quasi-stationary states of biopolymer
+ ensembles (Dyson, F. J. (1982) J. Mol. Evol. 18, 344-350).
+ Such emergent catalysis-driven, compositionally biased
+ entities may be viewed as having rudimentary "compositional
+ genomes." Our analysis addresses the question of how
+ mutually catalytic metabolic networks, devoid of
+ sequence-based biopolymers, could exhibit transfer of
+ chemical information and might undergo selection and
+ evolution. This computed behavior may constitute a
+ demonstration of natural selection in populations of
+ molecules without genetic apparatus, suggesting a pathway
+ from random molecular assemblies to a minimal protocell.},
+ pmid = {10760281},
+}
+@Article{Segre2001:compositional_inheritance,
+ author = {D Segr\'e and B Shenhav and R Kafri and D Lancet},
+ title = {The molecular roots of compositional inheritance},
+ journal = {J Theor Biol},
+ year = {2001},
+ volume = {213},
+ number = {3},
+ pages = {481--91},
+ month = {Dec},
+ abstract = {Non-covalent compositional assemblies, made of monomeric
+ mutually catalytic molecules, constitute an alternative to
+ alphabet-based informational biopolymers as a mechanism of
+ primordial inheritance. Such assemblies appear implicitly
+ in many "Metabolism First" origin of life scenarios, and
+ more explicitly in the Graded Autocatalysis Replication
+ Domain (GARD) model [Segré et al. (2000). Proc. Natl Acad.
+ Sci. U.S.A.97, 4112-4117]. In the present work, we provide
+ a detailed analysis of the quantitative molecular roots of
+ such behavior. It is demonstrated that the fidelity of
+ reproduction provided by a newly defined heritability
+ measure eta(*)(s), strongly depends on the values of
+ molecular recognition parameters and on assembly size. We
+ find that if the catalytic rate acceleration coefficients
+ are distributed normally, transfer of compositional
+ information becomes impossible, due to frequent
+ "compositional error catastrophes". In contrast, if the
+ catalytic acceleration rates obey a lognormal distribution,
+ as actually predicted by a statistical formalism for
+ molecular repertoires, high reproduction fidelity is
+ obtained. There is also a clear dependence on assembly size
+ N, whereby maximal eta is seen in a narrow range around N
+ approximately 3.5 N(G)/lambda, where N(G)is the size of the
+ primordial molecular repertoire and lambda is a molecular
+ interaction statistical parameter. Such relationships help
+ define the physicochemical conditions that could underlie
+ the early steps in pre-biotic evolution.},
+ pmid = {11735293},
+ doi = {10.1006/jtbi.2001.2440},
+}
+@Article{Segre2001:lipid_world,
+ author = {D Segre and D Ben-Eli and D W Deamer and D Lancet},
+ title = {The lipid world},
+ journal = {Orig Life Evol Biosph},
+ year = {2001},
+ volume = {31},
+ number = {1-2},
+ pages = {119--45},
+ month = {Feb-Apr},
+ abstract = {The continuity of abiotically formed bilayer membranes with
+ similar structures in contemporary cellular life, and the
+ requirement for microenvironments in which large and small
+ molecules could be compartmentalized, support the idea that
+ amphiphilic boundary structures contributed to the
+ emergence of life. As an extension of this notion, we
+ propose here a 'Lipid World' scenario as an early
+ evolutionary step in the emergence of cellular life on
+ Earth. This concept combines the potential chemical
+ activities of lipids and other amphiphiles, with their
+ capacity to undergo spontaneous self-organization into
+ supramolecular structures such as micelles and bilayers. In
+ particular, the documented chemical rate enhancements
+ within lipid assemblies suggest that energy-dependent
+ synthetic reactions could lead to the growth and increased
+ abundance of certain amphiphilic assemblies. We further
+ propose that selective processes might act on such
+ assemblies, as suggested by our computer simulations of
+ mutual catalysis among amphiphiles. As demonstrated also by
+ other researchers, such mutual catalysis within random
+ molecular assemblies could have led to a primordial
+ homeostatic system displaying rudimentary life-like
+ properties. Taken together, these concepts provide a
+ theoretical framework, and suggest experimental tests for a
+ Lipid World model for the origin of life.},
+ pmid = {11296516},
+}
+@Article{Shaikh2002:pe_phase_sm_area,
+ author = {Saame Raza Shaikh and Michael R Brzustowicz and Noah
+ Gustafson and William Stillwell and Stephen R Wassall},
+ title = {Monounsaturated PE does not phase-separate from the lipid raft
+ molecules sphingomyelin and cholesterol: role for
+ polyunsaturation?},
+ journal = {Biochemistry},
+ year = {2002},
+ volume = {41},
+ number = {34},
+ pages = {10593--602},
+ month = {Aug},
+ abstract = {We investigated interactions of the lipid raft molecules
+ sphingomyelin (SM) and cholesterol (CHOL) in monolayers and
+ bilayers composed of
+ 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylethanolamine
+ (POPE) or
+ 1-palmitoyl-2-docosahexaenoyl-sn-glycerophosphatidylethanol
+ amine (PDPE) at 35 degrees C. Techniques employed were
+ pressure-area (pi-A) isotherms generated from
+ Langmuir-Blodgett films, solid-state (2)H and (31)P NMR
+ spectroscopies, and differential scanning calorimetry
+ (DSC). Condensation calculated from pi-A isotherms and
+ reduction in the enthalpy of the gel-liquid-crystalline
+ transition in DSC scans showed CHOL has a strong affinity
+ for POPE, comparable to that observed between SM-CHOL.
+ Order parameters derived from (2)H NMR spectra of the
+ perdeuterated sn-1 chain of POPE-d(31) increased by >50\%
+ upon addition of equimolar CHOL to POPE-d(31)/SM (1:1 mol)
+ bilayers. Close proximity of CHOL to POPE even in the
+ presence of SM is indicated. Chemical shift anisotropy
+ (Deltasigma(csa)) measured from (1)H-decoupled (31)P NMR
+ spectra also implied intimate lipid mixing in POPE/SM/CHOL
+ (1:1:1 mol). In contrast, pi-A isotherms and corroborating
+ DSC studies of PDPE/SM (1:1 mol) indicate phase separation
+ between SM and PDPE, which was maintained in the presence
+ of CHOL. The cholesterol-associated increase in order of
+ the perdeuterated sn-1 chain of PDPE determined by (2)H NMR
+ was 2-fold less for PDPE-d(31)/SM/CHOL (1:1:1 mol) than
+ POPE-d(31)/SM/CHOL (1:1:1 mol). Our findings support the
+ notion that acyl chain dependent lateral phase separation
+ occurs in the presence of a docosahexaenoic acid
+ (DHA)-containing phospholipid (PDPE), but not an oleic
+ acid-containing phospholipid (POPE). We propose that
+ monounsaturated lipids do not promote formation of stable
+ lipid rafts and that polyunsaturation may be important for
+ raft stability.},
+ pmid = {12186543},
+}
+@Article{Shenhav2005:pgard,
+ author = {Barak Shenhav and Arren Bar-Even and Ran Kafri and Doron
+ Lancet},
+ title = {Polymer GARD: computer simulation of covalent bond formation
+ in reproducing molecular assemblies},
+ journal = {Orig Life Evol Biosph},
+ year = {2005},
+ volume = {35},
+ number = {2},
+ pages = {111--33},
+ month = {Apr},
+ abstract = {The basic Graded Autocatalysis Replication Domain (GARD)
+ model consists of a repertoire of small molecules,
+ typically amphiphiles, which join and leave a non-covalent
+ micelle-like assembly. Its replication behavior is due to
+ occasional fission, followed by a homeostatic growth
+ process governed by the assembly's composition. Limitations
+ of the basic GARD model are its small finite molecular
+ repertoire and the lack of a clear path from a 'monomer
+ world' towards polymer-based living entities. We have now
+ devised an extension of the model (polymer GARD or P-GARD),
+ where a monomer-based GARD serves as a 'scaffold' for
+ oligomer formation, as a result of internal chemical rules.
+ We tested this concept with computer simulations of a
+ simple case of monovalent monomers, whereby more complex
+ molecules (dimers) are formed internally, in a manner
+ resembling biosynthetic metabolism. We have observed events
+ of dimer 'take-over' - the formation of compositionally
+ stable, replication-prone quasi stationary states
+ (composomes) that have appreciable dimer content. The
+ appearance of novel metabolism-like networks obeys a
+ time-dependent power law, reminiscent of evolution under
+ punctuated equilibrium. A simulation under constant
+ population conditions shows the dynamics of takeover and
+ extinction of different composomes, leading to the
+ generation of different population distributions. The
+ P-GARD model offers a scenario whereby biopolymer formation
+ may be a result of rather than a prerequisite for early
+ life-like processes.},
+ pmid = {16010993},
+}
+@Article{Shenhav2007:comp_protocells,
+ author = {Barak Shenhav and Aia Oz and Doron Lancet},
+ title = {Coevolution of compositional protocells and their
+ environment},
+ journal = {Philos Trans R Soc Lond B Biol Sci},
+ year = {2007},
+ volume = {362},
+ number = {1486},
+ pages = {1813--9},
+ month = {Oct},
+ abstract = {The coevolution of environment and living organisms is well
+ known in nature. Here, it is suggested that similar
+ processes can take place before the onset of life, where
+ protocellular entities, rather than full-fledged living
+ systems, coevolve along with their surroundings.
+ Specifically, it is suggested that the chemical composition
+ of the environment may have governed the chemical
+ repertoire generated within molecular assemblies,
+ compositional protocells, while compounds generated within
+ these protocells altered the chemical composition of the
+ environment. We present an extension of the graded
+ autocatalysis replication domain (GARD) model--the
+ environment exchange polymer GARD (EE-GARD) model. In the
+ new model, molecules, which are formed in a protocellular
+ assembly, may be exported to the environment that surrounds
+ the protocell. Computer simulations of the model using an
+ infinite-sized environment showed that EE-GARD assemblies
+ may assume several distinct quasi-stationary compositions
+ (composomes), similar to the observations in previous
+ variants of the GARD model. A statistical analysis
+ suggested that the repertoire of composomes manifested by
+ the assemblies is independent of time. In simulations with
+ a finite environment, this was not the case. Composomes,
+ which were frequent in the early stages of the simulation
+ disappeared, while others emerged. The change in the
+ frequencies of composomes was found to be correlated with
+ changes induced on the environment by the assembly. The
+ EE-GARD model is the first GARD model to portray a possible
+ time evolution of the composomes repertoire.},
+ pmid = {17510019},
+ doi = {10.1098/rstb.2007.2073},
+}
+@Article{Smaby1997:pc_area_with_chol,
+ author = {J M Smaby and M M Momsen and H L Brockman and R E Brown},
+ title = {Phosphatidylcholine acyl unsaturation modulates the decrease
+ in interfacial elasticity induced by cholesterol},
+ journal = {Biophys J},
+ year = {1997},
+ volume = {73},
+ number = {3},
+ pages = {1492--505},
+ month = {Sep},
+ abstract = {The effect of cholesterol on the interfacial elastic
+ packing interactions of various molecular species of
+ phosphatidylcholines (PCs) has been investigated by using a
+ Langmuir-type film balance and analyzing the elastic area
+ compressibility moduli (Cs(-1)) as a function of average
+ cross-sectional molecular area. Emphasis was on the high
+ surface pressure regions (pi > or = 30 mN/m) which are
+ thought to mimic biomembrane conditions. Increasing levels
+ of cholesterol generally caused the in-plane elasticity of
+ the mixed monolayers to decrease. Yet, the magnitude of the
+ cholesterol-induced changes was markedly dependent upon PC
+ hydrocarbon structure. Among PC species with a saturated
+ sn-1 chain but different sn-2 chain cis unsaturation levels
+ [e.g., myristate (14:0), oleate (18:1delta9(c), linoleate
+ (18:2delta9,12(c), arachidonate (20:4delta5,8,11,14(c), or
+ docosahexenoate (22:6delta4,7,10,13,16,19(c)], the in-plane
+ elasticity moduli of PC species with higher sn-2
+ unsaturation levels were less affected by high cholesterol
+ mol fractions (e.g., >30 mol \%) than were the more
+ saturated PC species. The largest cholesterol-induced
+ decreases in the in-plane elasticity were observed when
+ both chains of PC were saturated (e.g., di-14:0 PC). When
+ both acyl chains were identically unsaturated, the
+ resulting PCs were 20-25\% more elastic in the presence of
+ cholesterol than when their sn-1 chains were long and
+ saturated (e.g., palmitate). The mixing of cholesterol with
+ PC was found to diminish the in-plane elasticity of the
+ films beyond what was predicted from the additive behavior
+ of the individual lipid components apportioned by mole and
+ area fraction. Deviations from additivity were greatest for
+ di-14:0 PC and were least for diarachidonoyl PC and
+ didocosahexenoyl PC. In contrast to Cs(-1) analyses,
+ sterol-induced area condensations were relatively
+ unresponsive to subtle structural differences in the PCs at
+ high surface pressures. Cs(-1) versus average area plots
+ also indicated the presence of cholesterol
+ concentration-dependent, low-pressure (<14 mN/m) phase
+ boundaries that became more prominent as PC acyl chain
+ unsaturation increased. Hence, area condensations measured
+ at low surface pressures often do not accurately portray
+ which lipid structural features are important in the
+ lipid-sterol interactions that occur at high membrane-like
+ surface pressures.},
+ pmid = {9284316},
+}
+@Article{Stano2010:vesicle_self_reproduction,
+ author = {Pasquale Stano and Pier Luigi Luisi},
+ title = {Achievements and open questions in the self-reproduction of
+ vesicles and synthetic minimal cells},
+ journal = {Chem Commun (Camb)},
+ year = {2010},
+ volume = {46},
+ number = {21},
+ pages = {3639--53},
+ month = {Jun},
+ abstract = {Supramolecular chemistry was enriched, about twenty years
+ ago, by the discovery of the self-reproduction of micelles
+ and vesicles. The dynamic aspects and complexity of these
+ systems makes them good models for biological compartments.
+ For example, the self-reproduction of vesicles suggests
+ that the growth in size and number of a vesicle population
+ resembles the pattern of living cells in several aspects,
+ but it take place solely due to physical forces. Several
+ reports demonstrate that reverse micelles, micelles,
+ sub-micrometric and giant vesicles can self-reproduce,
+ generating new particles at the expenses of a suitable
+ precursor. Recently, similar studies are in progress on
+ more complex vesicle-based systems, namely semi-synthetic
+ minimal cells. These are artificial cell-like compartments
+ that are built by filling liposomes with the minimal number
+ of biomolecules, such as DNA, ribosomes, enzymes, etc., in
+ order to construct a living cell in the laboratory. This
+ approach aims to investigate the minimal requirements for
+ molecular systems in order to display some living
+ properties, while it finds relevance in origins of life
+ studies and in synthetic (constructive) biology.},
+ pmid = {20442914},
+ doi = {10.1039/b913997d},
+}
+@Article{Svetina2009:vesicle_budding,
+ author = {Sasa Svetina},
+ title = {Vesicle budding and the origin of cellular life},
+ journal = {Chemphyschem},
+ year = {2009},
+ volume = {10},
+ number = {16},
+ pages = {2769--76},
+ month = {Nov},
+ abstract = {This Minireview provides an appropriate opportunity to
+ demonstrate the connection between the results of some
+ early experimental and theoretical investigations of
+ vesicle budding and the more recent application of the
+ concepts developed there to the process of vesicle
+ self-reproduction. Herein, we also explain why vesicle
+ budding could have preceded the establishment of cellular
+ life.},
+ pmid = {19774545},
+ doi = {10.1002/cphc.200900577},
+}
+@Article{Szostak2001:synthesizing_life,
+ author = {J W Szostak and D P Bartel and P L Luisi},
+ title = {Synthesizing life},
+ journal = {Nature},
+ year = {2001},
+ volume = {409},
+ number = {6818},
+ pages = {387--90},
+ month = {Jan},
+ pmid = {11201752},
+ doi = {10.1038/35053176},
+}
+@Article{Tamulis2011:lipid_world_evolution,
+ author = {Arvydas Tamulis and Mantas Grigalavicius},
+ title = {The emergence and evolution of life in a "fatty acid world"
+ based on quantum mechanics},
+ journal = {Orig Life Evol Biosph},
+ year = {2011},
+ volume = {41},
+ number = {1},
+ pages = {51--71},
+ month = {Feb},
+ abstract = {Quantum mechanical based electron correlation interactions
+ among molecules are the source of the weak hydrogen and Van
+ der Waals bonds that are critical to the self-assembly of
+ artificial fatty acid micelles. Life on Earth or elsewhere
+ could have emerged in the form of self-reproducing
+ photoactive fatty acid micelles, which gradually evolved
+ into nucleotide-containing micelles due to the enhanced
+ ability of nucleotide-coupled sensitizer molecules to
+ absorb visible light. Comparison of the calculated
+ absorption spectra of micelles with and without nucleotides
+ confirmed this idea and supports the idea of the emergence
+ and evolution of nucleotides in minimal cells of a
+ so-called Fatty Acid World. Furthermore, the
+ nucleotide-caused wavelength shift and broadening of the
+ absorption pattern potentially gives these molecules an
+ additional valuable role, other than a purely genetic one
+ in the early stages of the development of life. From the
+ information theory point of view, the nucleotide sequences
+ in such micelles carry positional information providing
+ better electron transport along the nucleotide-sensitizer
+ chain and, in addition, providing complimentary copies of
+ that information for the next generation. Nucleotide
+ sequences, which in the first period of evolution of fatty
+ acid molecules were useful just for better absorbance of
+ the light in the longer wavelength region, later in the PNA
+ or RNA World, took on the role of genetic information
+ storage.},
+ pmid = {20443139},
+ doi = {10.1007/s11084-010-9211-4},
+}
+@Article{Tanford1974:micelle_formation_thermodynamics,
+ author = {C Tanford},
+ title = {Thermodynamics of micelle formation: prediction of micelle
+ size and size distribution},
+ journal = {Proc Natl Acad Sci U S A},
+ year = {1974},
+ volume = {71},
+ number = {5},
+ pages = {1811--5},
+ month = {May},
+ abstract = {This paper presents a simple theory for the calculation of
+ micelle size and other properties of micelleforming
+ systems. The theory is based on the separate estimation of
+ the components of the free energy arising from hydrophobic
+ attraction and from head group repulsion, each as a
+ function of micelle size. The difficult problem of an a
+ priori calculation of the repulsive factor is circumvented
+ by using experimental values of this parameter, derived
+ from pressure-area curves of monolayers at an interface
+ between an aqueous solution and liquid hydrocarbon. Though
+ some parameters of the theory are still somewhat uncertain,
+ self-consistent and physically realistic values can be
+ assigned that lead to almost exact prediction of
+ experimental micelle sizes and critical micelle
+ concentrations for two distinctly different ionic
+ detergents.},
+ pmid = {4525294},
+}
+@article{Tewes2001:lipid_polarity_in_bec,
+ author = {BJ Tewes and HJ Galla},
+ title = {Lipid polarity in brain capillary endothelial cells.},
+ journal = {Endothelium},
+ year = 2001,
+ key = {bec, lipid polarity, lipid composition},
+ volume = 8,
+ number = 3,
+ pages = {207--220},
+ abstract = {Brain capillary endothelial cells (BCEC) represent an
+ epithelial like cell type with continuous tight
+ junctions and polar distributed proteins. In this paper
+ we investigated whether cultured BCEC show a polar
+ distribution of membrane lipids as this was demonstrated
+ for many epithelial cell types. Therefore we applied a
+ high yield membrane fractionation method to isolate pure
+ fractions of the apical and the basolateral plasma
+ membrane (PM) domains. Using a set of methods for lipid
+ analysis we were able to determine the total lipid
+ composition of the whole cells and the PM
+ fractions. Both membrane domains showed a unique lipid
+ composition with clear differences to each other and to
+ the whole cell composition. Three lipid species were
+ polar distributed between the two PM
+ domains. Phosphatidylcholine was enriched in the apical
+ membrane whereas sphingomyelin and glucosylceramide were
+ enriched in the basolateral membrane. The possible
+ function of this lipid polarity for the blood-brain
+ barrier mechanism is the generation of a suitable lipid
+ environment for polar distributed membrane proteins and
+ the generation of two PM domains with different
+ biophysical properties and permeabilities.},
+ pmid = 11824473
+}
+@Article{Thomas1988:chol_transfer,
+ author = {P D Thomas and M J Poznansky},
+ title = {Cholesterol transfer between lipid vesicles. Effect of
+ phospholipids and gangliosides},
+ journal = {Biochem J},
+ year = {1988},
+ volume = {251},
+ number = {1},
+ pages = {55--61},
+ month = {Apr},
+ abstract = {The effect of lipid composition on the rate of cholesterol
+ movement between cellular membranes is investigated using
+ lipid vesicles. The separation of donor and acceptor
+ vesicles required for rate measurement is achieved by
+ differential centrifugation so that the lipid effect can be
+ quantified in the absence of a charged lipid generally used
+ for ion-exchange-based separation. The rate of cholesterol
+ transfer from small unilamellar vesicles (SUVs) containing
+ 50 mol\% cholesterol to a common large unilamellar vesicle
+ (LUV) acceptor containing 20 mol\% cholesterol decreases
+ with increasing mol\% of sphingomyelin in the SUVs, while
+ phosphatidylethanolamine and phosphatidylserine have no
+ appreciable effect at physiologically relevant levels.
+ There is a large decrease in rate when
+ phosphatidylethanolamine constitutes 50 mol\% of donor
+ phospholipids. Interestingly, gangliosides which have the
+ same hydrocarbon moiety as sphingomyelin exert an opposite
+ effect. The effect of spingomyelin seems to be mediated by
+ its ability to decrease the fluidity of the lipid matrix,
+ while that of gangliosides may arise from a weakening of
+ phosphatidylcholine-cholesterol interactions or from a more
+ favourable (less polar) microenvironment for the desorption
+ of cholesterol provided by the head-group interactions
+ involving sugar residues. If the effect of asymmetric
+ transbilayer distribution of lipids is taken into
+ consideration, the observed composition-dependent rate
+ changes could partly account for the large difference in
+ the rates of cholesterol desorption from the inner and
+ outer layers of plasma membrane. Such rate differences may
+ be responsible for an unequal steady-state distribution of
+ cholesterol among various cellular membranes and
+ lipoproteins.},
+ pmid = {3390160},
+}
+@Article{Thurmond1991:area_of_pc_pe_2hnmr,
+ author = {R L Thurmond and S W Dodd and M F Brown},
+ title = {Molecular areas of phospholipids as determined by 2H NMR
+ spectroscopy. Comparison of phosphatidylethanolamines and
+ phosphatidylcholines},
+ journal = {Biophys J},
+ year = {1991},
+ volume = {59},
+ number = {1},
+ pages = {108--13},
+ month = {Jan},
+ abstract = {The role of lipid diversity in biomembranes is one of the
+ major unsolved problems in biochemistry. One parameter of
+ possible importance is the mean cross-sectional area
+ occupied per lipid molecule, which may be related to
+ formation of nonbilayer structures and membrane protein
+ function. We have used 2H NMR spectroscopy to compare the
+ properties of
+ 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphoethanolamine
+ (DPPE-d62) and
+ 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphocholine
+ (DPPC-d62) in the L alpha phase. We find that DPPE has
+ greater segmental order than DPPC, and that this increase
+ in order is related to the smaller area per acyl chain
+ found for DPPE. Values of the mean cross-sectional chain
+ area are calculated using a simple diamond lattice model
+ for the acyl chain configurational statistics, together
+ with dilatometry data. The results obtained for the mean
+ area per molecule are comparable with those from low angle
+ x-ray diffraction studies.},
+ pmid = {2015377},
+ doi = {10.1016/S0006-3495(91)82203-2},
+}
+@Article{Walde1994:fa_vesicle_reproduction,
+ author = {Peter Wlade and Roger Wick and Massimo Fresta and Annarosa Mangone and Pier Luigi Luisi},
+ title = {Autopoetic Self-Reproduction of Fatty Acid Vesicles},
+ journal = {J Am. Chem. Soc},
+ year = 1994,
+ volume = 116,
+ number = 26,
+ pages = {11649-11654},
+ abstract = {Conditions are described under which vesicles formed
+ by caprylic acid and oleic acid in water are able to
+ undergo autopoietic self-reproduction---namely an
+ increase of their population number due to reaction
+ which takes place within the spherical boundary of
+ the vesicles themselves. This is acchieved by
+ letting a certain amount of the neat water-insoluble
+ caprylic or oleic anhydride hydrolyze at alkaline
+ pH: the initial increase of the concentration of the
+ released acid/carboxylate is extremely slow (several
+ days to reach thte conditions for spontaneous
+ vesicle formation), but afterwards, the presence of
+ vesicles brings about a rapid second phase leading
+ to more and more vesicles being formed in an overall
+ autocatalystic process. THe catalytic power of the
+ caprylic acid and oleic acid vesicles toward the
+ hydrolysis of the correpsonding anhydride is
+ documented in a set of indepenedent experiments. In
+ these experiments, the hydroysis was carried out in
+ the presence of vesicles at a pH corresponding
+ approximately to the pK of the acid in the vesicles.
+ The process of autopoeitc self-reproduction of
+ caprylic acid and oleic acid vesicles is studied as
+ a function of temperature: by increasing temperature
+ (up to 70 C), the exponential time progress of
+ vesicle formation tend sot become steeper while the
+ long initial slow phase is significantly shortened.
+ The caprylic acid and oleic acid vesicles are
+ characterized by electron microscopy and by
+ determining their internal volume. The question
+ whether and to what extent these vesicles form a
+ classic chemical equilibrium system---in which
+ namely the free surfactant is in equilibrium with
+ the aggregates---is also investigated.},
+ doi = {10.1021/ja00105a004}
+}
+@Article{Wimley1990:dmpc_exchange,
+ author = {W C Wimley and T E Thompson},
+ title = {Exchange and flip-flop of dimyristoylphosphatidylcholine in
+ liquid-crystalline, gel, and two-component, two-phase large
+ unilamellar vesicles},
+ journal = {Biochemistry},
+ year = {1990},
+ volume = {29},
+ number = {5},
+ pages = {1296--303},
+ month = {Feb},
+ abstract = {The rate and extent of spontaneous exchange of
+ dimyristoylphosphatidylcholine (DMPC) from large
+ unilamellar vesicles (LUV) composed of either DMPC or
+ mixtures of DMPC/distearoylphosphatidylcholine (DSPC) have
+ been examined under equilibrium conditions. The phase state
+ of the vesicles ranged from all-liquid-crystalline through
+ mixed gel/liquid-crystalline to all-gel. The exchange rate
+ of DMPC between liquid-crystalline DMPC LUV, measured
+ between 25 and 55 degrees C, was found to have an Arrhenius
+ activation energy of 24.9 +/- 1.4 kcal/mol. This activation
+ energy and the exchange rates are very similar to those
+ obtained for the exchange of DMPC between DMPC small
+ unilamellar vesicles (SUV). The extent of exchange of DMPC
+ in LUV was found to be approximately 90\%. This is in
+ direct contrast to the situation in DMPC SUV where only the
+ lipid in the outer monolayer is available for exchange.
+ Thus, transbilayer movement (flip-flop) is substantially
+ faster in liquid-crystalline DMPC LUV than in SUV.
+ Desorption from gel-phase LUV has a much lower rate than
+ gel-phase SUV with an activation energy of 31.7 +/- 3.7
+ kcal/mol compared to 11.5 +/- 2 kcal/mol reported for SUV.
+ A defect-mediated exchange in gel-phase SUV, which is not
+ the major pathway for exchange in LUV, is proposed on the
+ basis of the thermodynamic parameters of the activation
+ process. Surprisingly, the rates of DMPC exchange between
+ DMPC/DSPC two-component LUV, measured over a wide range of
+ compositions and temperatures, were found to exhibit very
+ little dependence on the composition or phase configuration
+ of the vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)},
+ pmid = {2322564},
+}
+@Article{Wimley1991,
+ author = {W C Wimley and T E Thompson},
+ title = {Phosphatidylethanolamine enhances the concentration-dependent
+ exchange of phospholipids between bilayers},
+ journal = {Biochemistry},
+ year = {1991},
+ volume = {30},
+ number = {17},
+ pages = {4200--4},
+ month = {Apr},
+ abstract = {It has previously been demonstrated that lipid exchange
+ between phosphatidylcholine vesicles, at higher
+ concentrations, is characterized by a second-order
+ concentration-dependent exchange process in addition to the
+ first-order process operative at lower concentrations
+ (Jones, J. D., & Thompson, T. E. (1989) Biochemistry 28,
+ 129-134). Furthermore, it was demonstrated that the
+ second-order process occurs as a result of an enhancement
+ of the first-order desorption process, possibly resulting
+ from attractive interactions between a potentially
+ desorbing lipid molecule and a transiently apposed bilayer
+ (Jones, J. D., & Thompson, T. E. (1990) Biochemistry 29,
+ 1593-1600). In this work we have studied the exchange of
+ [3H]dimyristoylphosphatidylcholine (DMPC) between large
+ vesicles of the compositions 100\% DMPC, 70/30 (mol/mol)
+ DMPC/dimyristoylphosphatidylethanolamine (DMPE), and
+ 68.25/30/1.75 (mol/mol/mol)
+ DMPC/DMPE/dimyristoylphosphatidylglycerol (DMPG). The
+ second-order exchange process is enhanced by 100-fold or
+ more in vesicles containing 30 mol \% DMPE relative to
+ 100\% DMPC and is reduced or eliminated by the addition of
+ 1.75\% of the anionic lipid DMPG. These effects can be
+ achieved by alterations in the equilibrium bilayer
+ separation of 5 A or less. The results are in accord with
+ the model of Jones and Thompson and indicate that
+ relatively low concentrations of PE in a PC bilayer can
+ have significant effects on bilayer surface properties and
+ on potential interactions between bilayers.},
+ pmid = {2021612},
+}
+@Article{Wimley1991:dmpc_depc_exchange,
+ author = {W C Wimley and T E Thompson},
+ title = {Transbilayer and interbilayer phospholipid exchange in
+ dimyristoylphosphatidylcholine/dimyristoylphosphatidylethanolamine
+ large unilamellar vesicles},
+ journal = {Biochemistry},
+ year = {1991},
+ volume = {30},
+ number = {6},
+ pages = {1702--9},
+ month = {Feb},
+ abstract = {The rates of spontaneous interbilayer and transbilayer
+ exchange of [3H]dimyristoylphosphatidylcholine ([3H]DMPC)
+ were examined in DMPC and
+ DMPC/dimyristoylphosphatidylethanolamine (DMPE) large
+ unilamellar vesicles in the liquid-crystalline-, gel-, and
+ mixed-phase states. DMPC desorption rates from either gel
+ or liquid-crystalline phases containing DMPE are very
+ similar to the corresponding rates from pure DMPC gel or
+ liquid-crystalline phases. This is not the case for DMPC
+ desorption from distearoylphosphatidylcholine
+ (DSPC)-containing gel phases, where the desorption rates
+ are significantly faster than from a pure DMPC gel phase
+ [Wimley, W. C., & Thompson, T. E. (1990) Biochemistry 29,
+ 1296-1303]. We proposed that the DMPC/DSPC behavior results
+ from packing defects in gel phases composed of both DMPC
+ and DSPC molecules because of the four-carbon difference in
+ the acyl chain lengths of the two species. The present
+ results strongly support this hypothesis because no such
+ anomalous behavior is observed in DMPC/DMPE, which is
+ similar to DMPC/DSPC in phase behavior but does not have
+ the chain length difference. The inclusion of 10-30 mol \%
+ DMPE in DMPC bilayers was also found to have a significant
+ effect on the rate of transbilayer movement (flip-flop) of
+ [3H]DMPC in the liquid-crystalline phase. Between 10 and 30
+ mol \% DMPE, flip-flop of DMPC is slowed by at least
+ 10-fold relative to flip-flop in DMPC bilayers, and the
+ entropy and enthalpy of flip-flop activation are both
+ substantially decreased.(ABSTRACT TRUNCATED AT 250 WORDS)},
+ pmid = {1993185},
+}
projects / ool / lipid_simulation_formalism.git / commitdiff