ANNEXIN-II INHIBITS CALCIUM-DEPENDENT PHOSPHOLIPASE-A1 AND LYSOPHOSPHOLIPASE BUT NOT TRIACYL GLYCEROL LIPASE ACTIVITIES OF RAT-LIVER HEPATIC LIPASE

A member of the annexin family (the heterotetrameric annexin II2p11(2) complex purified from porcine intestinal epithelium) was tested for its ability to affect different calcium-dependent intrinsic lipolytic activities of rat liver hepatic lipase (HL). Whereas annexin II in the presence of calcium failed to interfere with HL triacyl glycerol lipase (EC 3.1.1.3) activity, it inhibited HL phospholipase A1 (EC 3.1.1.32) and lysophospholipase (EC 3.1.1.5) activities. Inhibition could be overcome by increasing the substrate concentration. Under phospholipase A1 assay conditions, annexin II did not bind to the purified HL enzyme. These results therefore suggest that only inhibitor/substrate interactions lead to inhibition of HL phospholipase A1 and lysophospholipase activities, an obviously general mechanism of phospholipase inhibition by annexins. Possible implications of HL inhibition in vivo by annexins are discussed.