Scanning calorimetric studies of aqueous dispersions of bilayers made with cholesterol and a pair of positional isomers of 3- sn-phosphatidylcholine

Abstract

Differential scanning calorimetric studies have been carried out on aqueous dispersions of cholesterol plus one of the pair of positional isomers, 1-arachidoyl-2-oleoylphosphatidylcholine (AOPC) or 1-oleoyl-2-arachidoylphosphatidylcholine (OAPC). There were some differences in the shapes of the endotherms obtained from the dispersions with the two positional isomers. These observations confirm the previous finding (Davis, P.J. and Keough, K.M.W. (1984) Biochemistry 22, 6334–6340) that positional isomers of unsaturated phosphatidylcholines may interact differently with cholesterol, at least in the gel state. The shapes of endotherms obtained here and in the previous study are consistent with the suggestion that the position of the unsaturated chain on the glycerol has a role in determining the nature of the phosphatidylcholine-cholesterol interaction. Certain features of the endotherms seen here and previously (op. cit.) suggest that factors such as effective chain depth in the bilayer or efficiency of chain packing in the bilayer may also influence this interaction.