STUDIES ON LECITHIN-CHOLESTEROL-WATER INTERACTIONS BY DIFFERENTIAL SCANNING CALORIMETRY AND X-RAY DIFFRACTION

Addition of cholesterol to dipalmitoyl-l-lecithin in water lowers the transition temperature between the gel and liquid crystalline phase, and decreases the heat absorbed at the transition. No transition is observed with an equimolar ratio of the lecithin with cholesterol. This ratio corresponds to the maximum amount of cholesterol which can be introduced before cholesterol precipitation occurs. Unsaturated lecithins and the lipid extract of human erythrocyte ghosts exhibit similar behaviour. The cholesterol controls the fluidity of the hydrocarbon chains of the phospholipid by disruption of the crystalline chain lattice of the gel phase, and by inhibiting the flexing of chains in the dispersed liquid crystalline phase. The possible implications of this behaviour to the role of cholesterol in biological membranes are discussed. © 1968.