Phospholipase A2: Comparative Action of Three Different Enzyme Preparations on Selected Lipoprotein Systems

Abstract

The actions of phospholipase A2 preparations from a snake venom (Crotalus adamanteus) and from beef and human pancreas on selected lipoproteins have been compared. The mammalian enzymes were inhibited by Na+ and K+ ions, an effect which may be explained by their relatively high isoelectric points. The venom enzyme exhibited a higher specific activity when acting on beef serum than was observed with any of the other substrates tested. The pancreatic enzymes did not hydrolyze beef serum phospholipids. None of the enzyme preparations was capable of attacking intact beef erythrocytes. The results indicate that different phospholipases are highly specific in their action on various lipoproteins.The venom enzyme hydrolyzed phosphatidylcholine and phosphatidylethanolamine at equivalent rates in egg yolk suspensions in isotonic saline or rat brain homogenates in isotonic sucrose, while the enzyme from beef pancreas preferentially attacked phosphatidylethanolamine in these lipoproteins. The pancreatic enzymes were more effective in producing lysophosphatides in brain homogenates than the venom phospholipase A2, and the specific activity of the enzyme from human pancreas was higher with this substrate than any other. It also hydrolyzed phosphatidylethanolamine at a more rapid rate than other phospholipids, including phosphatidylcholine, phosphatidylserine, and the ethanolamine plasmalogens. Lysophosphatide production was assessed quantitatively in the experiments involving the egg yolk and brain homogenate preparations.