Non-random distribution of cholesterol in phosphatidyl-choline bilayers

Abstract 1. 1. The effect of cholesterol upon the phase transition occurring in various mixtures of synthetic disaturated phosphatidylcholines with fatty acid constituents of 12, 14, 16, and 18 carbon atoms was measured by differential scanning calorimetry. 2. 2. Mixtures which differ 2 carbon atoms show cocrystallisation of the paraffin chains. In these mixtures cholesterol interacts randomly with the various phosphatidylcholine species. 3. 3. Mixtures which differ 4 or more carbon atoms show monotectic behaviour (phase separation). In these mixtures cholesterol interacts preferentially with the phosphatidylcholine species with the lowest transition temperature. This results in a non-random distribution of cholesterol at temperatures at which phase separation occurs. The implications of these findings for cholesterol-containing biological membranes are discussed.