Identification of domains of phosphatidylcholine in human erythrocyte plasma membranes. Differential action of acidic and basic phospholipases A2 from Agkistrodon halys blomhoffii.

Abstract

Highly purified acidic (pI 4.9) and basic (pI 8.7) phospholipases A2 from snake (Agkistrodon halys blomhoffii) venom hydrolyzed approximately 20% and 60%, respectively, of the phosphatidylcholine (PC) of intact human erythrocytes prior to hemolysis. Sequential use of the acidic enzyme followed by the basic phospholipase A2 or vice versa manifested a characteristic PC hydrolysis pattern. For example, when acidic enzyme had hydrolyzed nearly 20% of this substrate, a subsequent treatment with the basic enzyme hydrolyzed only an additional 40% of the PC before hemolysis. On the other hand, in experiments where hydrolysis of about 20% of PC of erythrocytes was achieved by a short term incubation with the basic enzyme, then a further treatment of the same cells with the acidic enzyme caused only 10% additional PC hydrolysis before hemolysis. This demonstrated that the acidic enzyme hydrolyzed one domain of PC in the intact erythrocytes, whereas the basic enzyme hydrolyzed not only the same but also another domain of PC in membranes. Analysis of fatty acids released by the action of these two phospholipases A2 on erythrocytes indicated further characteristic differences. In particular, the ratio of released saturated to unsaturated fatty acids was significantly higher with the acidic enzyme as compared with the basic phospholipase A2. These results provide firm support to the conclusion that there are different domains of PC in human erythrocyte membranes and that the acidic and basic phospholipase A2 of A. halys blomhoffii can be used to identify them.