Evidence for an Asymmetric Distribution of Phospholipids in the Human Erythrocyte Membrane

The changes in phospholipid composition of the inner (cytoplasmic) surface of the human erythrocyte membrane resulting from the digestion of sealed inside-out vesicles with phospholipases A 2 and C were determined. Virtually all of the phosphatidylethanolamine and phosphatidylserine and 30–40% of the phosphatidylcholine and sphingomyelin of inside-out vesicles were found to be accessible to enzyme hydrolysis. In contrast, all of the above phospholipids of unsealed ghosts were susceptible to phospholipolytic digestion. These results are a direct demonstration of an asymmetric distribution of phospholipids in the human erythrocyte membrane.