ACTION OF PHOSPHOLIPASE A ON PLASMA MEMBRANES OF RAT LIVER CELLS

Isolated liver cells were treated with snake venom phospholipase A to obtain information on the relative importance of different phospholipids in the plasma membrane to its structural stability. The hydrolysis of phosphatidylethanolamine and lecithin by phospholipase A from Naia naia produced a change in the permeability of the liver cell plasma membrane which was arbitrarily assessed by measuring the amount of the intracellular enzyme glutamic oxaloacetic transaminase released into the incubation medium. There was only a small leakage of glutamic oxaloacetic transaminase from the cell until 25–35% of the phosphatidylethanolamine had been hydrolysed. Further hydrolysis caused a rapid increase in the release of the enzyme. Very little lecithin was hydrolysed by the same enzyme concentrations. After treatment with phospholipase A the cells were stained with either acridine orange, eosin or nigrosin and examined by light, phase contrast and fluorescent microscopy. Their gross morphology appeared to be unaltered by the hydrolysis of up to 50–60% of the cell phosphatidylethanolamine. The results suggest that phosphatidylethanolamine is relatively more important than lecithin in maintaining, in terms of permeability to a protein molecule, the structural integrity of the liver cell plasma membrane. Copyright © 1968, Wiley Blackwell. All rights reserved