Abstract
Studies of monolayer mixtures of certain phospholipids with cholesterol by epifluorescence microscopy and measurement of cholesterol desorption show evidence for the formation of "condensed complexes." A thermodynamic model of these complexes has been developed and has been shown to be generally consistent with observed phase diagrams, cholesterol desorption rates, and electric field susceptibility. Previous work has shown that complexes comprising 10-50 molecules provide good agreement with experimental results. The present study examines the calculated properties of complexes containing very large numbers of molecules and extends the condensed complex model to incorporate the formation of complexes of variable size. Trends in equilibrium composition are similar to those calculated for small complexes. Thermal transitions are continuous, with a strong composition dependence of the breadth of the transition. The average number of molecules in a large complex shows a pronounced dependence on the composition of the reaction mixture. Large complexes have properties of a separate thermodynamic phase.
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Selected References
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- Anderson T. G., McConnell H. M. Condensed complexes and the calorimetry of cholesterol-phospholipid bilayers. Biophys J. 2001 Nov;81(5):2774–2785. doi: 10.1016/S0006-3495(01)75920-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Brown D. A., London E. Structure and function of sphingolipid- and cholesterol-rich membrane rafts. J Biol Chem. 2000 Jun 9;275(23):17221–17224. doi: 10.1074/jbc.R000005200. [DOI] [PubMed] [Google Scholar]
- Hinz H. J., Sturtevant J. M. Calorimetric investigation of the influence of cholesterol on the transition properties of bilayers formed from synthetic L- -lecithins in aqueous suspension. J Biol Chem. 1972 Jun 10;247(11):3697–3700. [PubMed] [Google Scholar]
- Ipsen J. H., Karlström G., Mouritsen O. G., Wennerström H., Zuckermann M. J. Phase equilibria in the phosphatidylcholine-cholesterol system. Biochim Biophys Acta. 1987 Nov 27;905(1):162–172. doi: 10.1016/0005-2736(87)90020-4. [DOI] [PubMed] [Google Scholar]
- McMullen T. P., Lewis R. N., McElhaney R. N. Differential scanning calorimetric study of the effect of cholesterol on the thermotropic phase behavior of a homologous series of linear saturated phosphatidylcholines. Biochemistry. 1993 Jan 19;32(2):516–522. doi: 10.1021/bi00053a016. [DOI] [PubMed] [Google Scholar]
- Radhakrishnan A., Anderson T. G., McConnell H. M. Condensed complexes, rafts, and the chemical activity of cholesterol in membranes. Proc Natl Acad Sci U S A. 2000 Nov 7;97(23):12422–12427. doi: 10.1073/pnas.220418097. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Radhakrishnan A., McConnell H. M. Chemical activity of cholesterol in membranes. Biochemistry. 2000 Jul 18;39(28):8119–8124. doi: 10.1021/bi0005097. [DOI] [PubMed] [Google Scholar]
- Radhakrishnan A., McConnell H. M. Condensed complexes of cholesterol and phospholipids. Biophys J. 1999 Sep;77(3):1507–1517. doi: 10.1016/S0006-3495(99)76998-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Radhakrishnan A., McConnell H. M. Electric field effect on cholesterol-phospholipid complexes. Proc Natl Acad Sci U S A. 2000 Feb 1;97(3):1073–1078. doi: 10.1073/pnas.97.3.1073. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Simons K., Ikonen E. Functional rafts in cell membranes. Nature. 1997 Jun 5;387(6633):569–572. doi: 10.1038/42408. [DOI] [PubMed] [Google Scholar]
- Thewalt J. L., Bloom M. Phosphatidylcholine: cholesterol phase diagrams. Biophys J. 1992 Oct;63(4):1176–1181. doi: 10.1016/S0006-3495(92)81681-8. [DOI] [PMC free article] [PubMed] [Google Scholar]