Cholesterol-multilipid interactions in bilayers.
To extend our knowledge of model membrane systems based upon one lipid component, multi-lamellar bilayers were made of cholesterol with two phospholipids in equimolar ratio, and the enthalpy change delta H of the main phase transition of the temary mixture was measured by differential scanning calorimetry (DSC) as a function of increasing cholesterol concentration c. The lipids were saturated phosphatidylcholines CnPC of acyl chain length n, and as the n of the two lipids became more different (from C13PC/C14PC to C14PC/C15PC to C14PC/C18PC to C14PC/C19PC) distinct breaks in the delta H versus c plots were observed. These mixtures displayed only one broad DSC endotherm. Mixtures of an unsaturated lipid C18: 1PC (dioleoyl) with C16PC or with C18PC showed two peaks, with each peak being associated with its parent lipid. However, the delta H versus c plots for each of these peaks showed an initial independence of cholesterol concentration followed by a dependence on cholesterol concentration. These results indicate that, in lipid mixtures, the type of interaction of cholesterol with each lipid component depends on the concentration of cholesterol present.
Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104.
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Finegold
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Singer
D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry; D013816:Thermodynamics
D008051:Lipid Bilayers; D010743:Phospholipids; D002784:Cholesterol