Selective inhibition of phospholipase A2 by different lipocortins

Different lipocortins, purified from pig lung and from cultured bone marrow-derived macrophages showed a high degree of specificity for distinct phospholipids, when assayed for anti-phospholipase A2 activity. The 34-kDa fraction from lung inhibited pancreas phospholipase A2 only if phosphatidylethanolamine was used as substrate, whereas the 68-kDa lung fraction was inhibitory only when phosphatidylcholine was the substrate. A comparison of phospholipases A2 from different sources (pancreas and macrophages) revealed different inhibitory properties of lipocortins when assayed with the same substrate. Using phosphatidylcholine as substrate, the 68-kDa lung fraction only inhibited the pancreas enzyme. On the other hand with phosphatidylethanolamine as substrate, the 34-kDa macrophage lipocortin exerted inhibition on phospholipase A2, purified from macrophages, but did not affect the pancreas enzyme. These data suggest a complex interaction consisting of specific binding of individual lipocortins to distinct phospholipids but also suggest that lipocortins interact with the enzyme as well.