Diacylglycerol stimulates the Ca2(+)-dependent phospholipase A2 of ram spermatozoa.

We have investigated phospholipase A2 (PLA2) activity in sonicates from ram spermatozoa and have analyzed the enzyme's susceptibility both to various inhibitors and to stimulation by diacylglycerols (DAGs). Ram sperm PLA2 activity was Ca2(+)-dependent and was inhibited by dexamethasone, chloracysine and compounds Ro 31-4493 and Ro 31-4639; mepacrine, however, did not inhibit PLA2 activity. Addition of three different 1,2-DAGs (dioctanoyl-sn-glycerol, oleoyl-acetyl-sn-glycerol and dioleoyl-sn-glycerol) markedly increased PLA2 activity; moreover, both 1,2- and 1,3-isomers enhanced enzyme activity. Since ram spermatozoa lack active protein kinase C, the target of DAG in most cells, our results suggest that stimulation of PLA2 activity by DAG may play an important role in intracellular signalling in the sperm cell.