Novel seminal phospholipase A(2) is inhibited by the major proteins of bovine seminal plasma

The activity of a novel phospholipase A(2), isolated from bovine seminal plasma, was completely inhibited by low concentrations of the major proteins of bovine seminal plasma (BSP proteins). The inhibition was observed towards micellar as well as liposomal phosphatidylcholine. By solid phase binding assay it was determined that the inhibition involved a reduced accessibility to the lipidic substrate. Since the HSP proteins interact with choline phospholipids and since this interaction can be prevented by low concentrations of free choline, the effect of choline on the inhibition was studied. Choline could only partially relieve, even at high concentrations, the phospholipase A(2) inhibition. The reduced accessibility appears to proceed via two distinct interactions: binding to the substrate on one hand and to the enzyme on the other hand. These results indicate that the BSP proteins may act as spermatozoa stabilizing agents by preventing premature lipolysis of the sperm surface. (C) 1997 Elsevier Science B.V.