Purification of an acrosin-like enzyme from sea urchin sperm

Sea urchin sperm contain an acrosin-like enzyme with an apparent molecular weight of 53,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals two subunits of 34,000 daltons and 18,000 daltons. The Mr = 34,000 subunit is the catalytic entity as revealed both by labeling with [14C]diisopropyl phosphorofluoridate and by proteolytic activity after dissociation of the subunits at pH 2.5. Both the 34,000-dalton and the 53,000-dalton forms of the enzyme catalyze the hydrolysis of N alpha-benzoyl-L-arginine ethyl ester and both are inactivated by inhibitors of low molecular weight, whereas only the Mr = 34,000 form is inactivated by large proteinaceous inhibitors. Only the Mr = 34,000 form catalyzes proteolysis of denatured lysozyme or the B chain of insulin. The Mr = 18,000 subunit appears to suppress the proteolytic activity but not the activity toward the small ester substrate. These findings are discussed in terms of possible roles of this enzyme in the control of early events leading to fertilization.