Comparison of human acrosin, a trypsin-like sperm proteinase, with human pancreatic trypsin: temperature stability and effect of cations.

Temperature and ion sensitivity of human acrosin (EC 3.4.21.10) was compared to that of human trypsin. With the exception of zinc, no ion tested had significant effects on either enzyme. Zinc behaved as a noncompetitive inhibitor of both enzymes, with inhibition constants of 1.8 and 1.7 mM for acrosin and trypsin respectively. Trypsin was inhibited by the chelators EDTA and EGTA, a specific effect reversed by either calcium or magnesium. EDTA inhibited acrosin in a nonspecific manner, while EGTA was without effect. Unlike acrosin from the other species, human acrosin was unaffected by calcium or the polyamines, spermine and spermidine. Acrosin was sensitive to inhibition by preincubation temperatures above 5 degrees C; trypsin, however, was stable to preincubation temperatures up to 60 degrees C. Hydrolysis of N-alpha-benzoyl-L-arginine ethyl ester was more efficiently catalyzed by trypsin (6800 cal/mol) than by acrosin (9511 cal/mol).