On the Specificity of a Phospholipase A2 Purified from the 106,000 X G Pellet of Bovine Brain

Assessment has been made of the specificity of a purified phospholipase A2 from the 106,000 X g pellet (microsomal fraction) of bovine grey matter which shows strong activity toward phosphatidylinositol (PI). In the first series of experiments involving the utilization as substrates of PI with different 14C- or 3H-labeled fatty acids in the 2-position, the purified phospholipase A2 most readily removed 16:0 palmitic acid, followed by 18:0 stearic acid, 18:1 oleic acid and 20:4 arachidonic acid. In the second series of experiments, the purified phospholipase A2 showed preferential action toward PI (100%) compared to phosphatidylcholine (PC, 62.5%), phosphatidic acid (PA, 32.6%), phosphatidylethanolamine (PE, 25.1%) and phosphatidylserine (PS, 21.5%), where each phosphoglyceride was labeled in the 2-position with [1-14C] oleic acid. In the third series of experiments, fatty acids were shown to cause inhibition of action of the purified phospholipase A2 on 1-acyl, 2-[1-14C] oleoyl PI in the order 20:4 greater than 18:1 greater than 18:0 greater than 16:0 which is the reverse order to that just noted. In the final series of experiments, the addition of the phosphoglycerides PC, PE, PS and PA in amounts of 5 or 10 microM caused either no inhibition (PE, 2%), slight inhibition (PC, 15%) or reasonably significant inhibition (PA, 20% and PS, 40%) of action of the purified phospholipase A2 on 1-acyl, 2-[1-14C]-oleoyl PI. The pattern of specificity observed for the purified phospholipase A2 combined with its microsomal location are the expected properties of a phospholipase A2 that might function in a deacylation-reacylation cycle for modifying the fatty acid distribution in PI.