Effect of phospholipase A 2 on rat liver microsomal diacylglycerol cholinephosphotransferase, diacylglycerol ethanolaminephosphotransferase and diacylglycerol acyltransferase

Abstract

Rat liver microsomes were treated with snake venom ( Naja naja) phospholipase A 2. Effect of the degradation of microsomal major phospholipids were studied on the activities of diacylglycerol cholinephosphotransferase (EC 2.7.8.2), diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1) and diacylglycerol acyltransferase (EC 2.3.1.20). The activities of cholinephosphotransferase and diacylglycerol acyltransferase were rapidly lost following the accumulation of lysophospholipids and free fatty acid, whereas ethanolaminephosphotransferase activity remained unaffected even when over 90% and almost 100% of microsomal phosphatidylcholine and phosphatidylethanolamine, respectively, were hydrolyzed. The inactivation of diacylglycerol acyltransferase occurred much more rapidly than that of cholinephosphotransferase. Microsomal total phospholipids partially reactivated the treated cholinephosphotransferase, but not diacylglycerol acyltransferase. Among phospholipids tested, only phosphatidylcholine was effective. Albumin could partially restore the inactivated diacylglycerol acyltransferase. Ethanolaminephosphotransferase became by the treatment extremely heat-labile, and was restabilized by removal of lysophospholipids and fatty acids from the microsomal membranes. These results indicate that the three diacylglycerol-utilizing enzymes have different dependences on membrane phospholipids and that they are affected differently by the degradation products formed through the action of phospholipase A 2.