Oligomerisation of boar acrosin

Boar acrosin, a glycoprotein present in the acrosome of spermatozoa, tends to aggregate in the absence of detergents and lipids. Self-association products were analyzed electrophoretically by the method of Ferguson. Molecular weights ranging from 44 000 up to 237 000 were found, corresponding to acrosin monomer up to hexamer. Involvement of the active site of the serine proteinase in the formation of oligomers was demonstrated by active enzyme staining and determination of amidase activity of aggregated acrosin. Only monomeric acrosin proved to have full activity, while a marked decrease in specific activity was found upon aggregation. Hence, evidence is presented that acrosin has hydrophobic binding sites modulating the proteinase activity.