Thermal behavior of synthetic sphingomyelin-cholesterol dispersions.
The thermotropic behavior of aqueous dispersions of palmitoylsphingomyelin-cholesterol and lignoceryl-sphingomyelin-cholesterol mixtures has been examined by high-sensitivity differential scanning calorimetry. When less than 25 mol % cholesterol is mixed with either sphingomyelin, the calorimetric endotherm is composed of a sharp and a broad component. The sharp-component enthalpy change decreases as the mole percent cholesterol increases with the extrapolated zero enthalpy point being 25 to 30 mol %. With palmitoylsphingomyelin, the temperature of maximum heat capacity of the sharp component decreases monotonically with increasing cholesterol content, while the lignocerylsphingomyelin sharp-component maximum remains constant until more than 20 mol % sterol is present. The broad-component enthalpy change maximizes at 3--4 kcal/mol between 10 and 20 mol % cholesterol and decreases as the ratio of cholesterol is increased or decreased from this range for both sphingomyelins. The results are compared with those from a previous study on dipalmitoylphosphatidylcholine-cholesterol mixtures and are interpreted as evidence for the coexistence of cholesterol-rich and cholesterol-poor phases.
D000818:Animals; D002152:Calorimetry, Differential Scanning; D002784:Cholesterol; D005227:Fatty Acids / Q000032:analysis; D006801:Humans; D008567:Membranes, Artificial; D013109:Sphingomyelins; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
D005227:Fatty Acids; D008567:Membranes, Artificial; D013109:Sphingomyelins; D002784:Cholesterol