Characterization of heparin low-affinity phospholipase A(1) present in brain and testicular tissue

We identified a unique phospholipase A (PLA) with relatively low heparin af finity, which was distinguishable from the heparin-binding secretory PLA,s, in rat, mouse, and bovine brains and testes. The partially purified enzyme was Ca2+-independent at neutral pH but Ca2+-dependent at alkaline pH. It p redominantly hydrolyzed phosphatidic acid (PA) in the presence of Triton X- 100 and phosphatidylethanolamine (PE) in its absence. When rat brain-derive d endogenous phospholipids were used as a substrate, the enzyme released sa turated fatty acids in marked preference to unsaturated ones. Consistent wi th this observation, the enzyme hydrolyzed sn-1 ester bonds in the substrat es about 2,000 times more efficiently than sn-2 ones, thereby acting like P LA(1), The enzyme also exhibited weak but significant sn-1 lysophospholipas e activity. On the basis of its limited tissue distribution, substrate head group specificity and immunochemical properties, this enzyme appears to be identical to the recently cloned PA-preferring PLA(1).