Sphingomyelinases in human, bovine and porcine seminal plasma

The seminal plasma of man, boar and bull was found to have a sphingomyelinase (SMase) activity hydrolysing N-methyl-14C]sphingomyelin. The human and porcine enzymes had an acid pH optimum and were not influenced by divalent metal ions or chelating agents. They were closely similar with the lysosomal enzyme in many tissues. The bovine seminal plasma SMase was partially purified. The enzyme was a glycoprotein with pH optimum at 6.5, a broad pI 4.2-4.8 and molecular mass of 160 and 60 kDa, respectively, in native and SDS-PAGE. The enzyme was activated by Co greater than Mn greater than Cd greater than Ni and inhibited by chelating agents, Cu, Fe, Pb and Zn. The enzyme was clearly distinct from the acid lysosomal SMase and the previously described neutral Mg2+-dependent and independent activities. It had a wide distribution in the bull reproductive tissues.