PLATELET-ACTIVATING-FACTOR ACETYLHYDROLASE ACTIVITY IN BOVINE SEMINALPLASMA

Platelet-activating factor (PAF) is a potent signaling molecule that h as been detected in mammalian sperm from several species. The biologic al function of sperm-derived PAF and mechanisms controlling its produc tion have not been clearly defined. In the remodeling pathway for PAF biosynthesis, PAF is produced by phospholipase A(2) hydrolysis of 1-0- alkyl phospholipids followed by acetylation by PAF acetyltransferase. PAF is inactivated by PAF acetylhydrolase. PAF acetylhydrolase activit y has been detected recently in human seminal plasma, where it may pla y a role in regulating PAF production or content by sperm. The purpose of this study was to measure and partially characterize PAF acetylhyd rolase in bovine seminal plasma. Acetylhydrolase activity was detected in seminal plasma, was linear with time and protein concentration, an d had a specific activity of 122 nmol/minute/mg protein. The enzyme wa s cation independent and was not inhibited by phosphatidylcholine but was inhibited by p-bromophenacylbromide and partially inhibited by phe nylmethylsulfonylfluoride. Very little acetylhydrolase activity was de tected in caudal epididymal fluid or caudal epididymal sperm. Enzyme a ctivity associated with ejaculated sperm was largely removed by their centrifugation through Percoll and subsequent washing. These results d emonstrate very high PAF acetylhydrolase activity in bovine seminal pl asma. The enzyme appears to be of accessory gland origin and has prope rties similar to those of the enzyme from other sources.