The preferential interaction of cholesterol with different classes of phospholipids.

1. By differential scanning calorimetry a preferential affinity of cholesterol for sphingomyelin was established in mixtures of sphingomelin and phosphatidylcholine where sphingomyelin was either the higher or the lower melting phospholipid. 2. A preferential affinity of cholesterol for sphingomyelin was also found in mixtures of sphingomyelin and phosphatidylethanolamine where sphingomyelin was either the higher or the lower melting phospholipid. The sphingomyelin used was isolated from beef erythrocytes or synthetic palmitoyl sphingomyelin. 3. In mixtures of phosphatidylserine with phosphatidylethanolamine, or phosphatidylserine with phosphatidylcholine, cholesterol showed the highest affinity for the lower melting phospholipid. 4. In a previous paper (van Dijck et al. (1976) Biochim. Biophys. Acta 455, 576-588) it was established that cholesterol has a higher affinity for phosphatidylcholine than for phosphatidylethanolamine. The affinity order of cholesterol for the neutral phospholipids which can be deduced form these experiments is sphingomyelin greater than phosphatidylcholine greater than phosphatidylethanolamine.