Transverse asymmetry of phospholipids in subcellular membranes of rat liver.

Subcellular membranes isolated from rat liver in a form impermeable to macromolecules were treated with phospholipase A2 from Naja naja venom. The phosphatidylserine, phosphatidylethanolamine and about half of the phosphatidylcholine of microsomes, Golgi membranes, inner mitochondrial membranes, lysosomes and nuclear membranes were hydrolyzed. It is proposed that these phospholipids are localized in the outer surface of the membrane bilayer, which represents the cytoplasmic side in the living cell, while the remaining phosphatidylcholine and most of the phosphatidylinositol, sphingomyelin and cardiolipin may be assigned to the inner side of the bilayer.