Negatively charged phospholipids and their position in the cholesterol affinity sequence.

The effects of low concentrations of cholesterol in mixtures of a negatively charged phospholipid (phosphatidylserine or phosphatidylglycerol) and another phospholipid (phosphatidylcholine, sphingomyelin or phosphatidylethanolamine) have been studied by differential scanning calorimetry. Only mixtures which showed a gel phase miscibility gap have been employed. It was demonstrated that in mixtures with phosphatidylethanolamine, cholesterol was preferentially associated with the negatively charged phospholipid, regardless whether this species represented the component with the high or with the low transition temperature in the mixture. In mixtures of a negatively charged phospholipid and phosphatidylcholine, cholesterol associated with the negatively charged phospholipid; when the phosphatidylcholine was the species with the low transition temperature, cholesterol had an affinity for the phosphatidylcholine and for the negatively charged phospholipid as well. Cholesterol, in a mixture of sphingomyeline with a high and phosphatidylserine with a low transition temperature, was preferentially associated with sphingomyelin. From these experiments it is concluded that phospholipids show a decrease in affinity for cholesterol in the following order: sphingomyelin greater than phosphatidylserine, phosphatidylglycerol greater than phosphatidylcholine greater than phosphatidylethanolamine.