THERMOTROPIC BEHAVIOR OF PHOSPHATIDYLCHOLINE GLUCOSYL CERAMIDE MIXTURES - EFFECTS OF PHOSPHOLIPID ACYL-CHAIN COMPOSITION AND INTERACTION WITH WATER

The thermotropic behavior of multilamellar vesicles composed of mixtur es of dimyristoyl phosphatidylcholine-glucosyl ceramide and of egg pho sphatidylcholine-glucosyl ceramide was investigated using differential scanning calorimetry. Macroscopic demixing of the lipid components oc curred when multilamellar vesicles were prepared from mixtures of gluc osyl ceramide and egg phosphatidylcholine by conventional methods. Thi s problem was overcome by a technique based on spray drying of the lip id mixture. The results obtained for the two systems are compared with data available for dipalmitoyl phosphatidylcholine-glucosyl ceramide mixtures (Biochemistry 22 (1983) 3497-3501). All three phosphatidylcho lines perturb the complex thermotropic behavior of glucosyl ceramide. The data suggest that the interference with intermolecular interaction s among glycosyl ceramide molecules by phospholipid molecules is relat ed to the molecular miscibility of the two components. This is strongl y dependent on the acyl chain composition of the phosphatidylcholine a nd the water activity of the ambient aqueous phase.