Properties of a Proteolytic Enzyme From Rabbit Sperm Acrosomes

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Abstract
Acrosin is a proteolytic enzyme extractable from sperm acrosomes and essential for penetration of the zona pellucida of the ovum by spermatozoa. It has properties in common with both trypsin and plasmin having an optimum pH of 8.0, hydrolyzing benzoyl arginine ethyl ester (BAEE) and tosyl arginine methyl ester (TAME) but not benzoyl tyrosine ethyl ester (BTEE), or acetyl tyrosine ethyl ester (ATEE), being stimulated by calcium ions and stable at pH 3.0. Acrosin differs from pancreatic trypsin in that it hydrolyzes BAEE more rapidly than TAME, is less effectively inhibited by ovomucoid and pancreatic trypsin inhibitor, has a higher molecular weight, undergoes rapid loss of activity even in the presence of calcium and produces fewer peptides on incubation with oxidized ribonuclease. One of two trypsin inhibitors isolated from guinea pig seminal vesicles inhibits acrosin and trypsin but not plasmin, whereas the other inhibits all three enzymes. Acrosin further differs from plasmin in that it has a different molecular weight and is more unstable. Inhibition by diisopropyl fluorophosphate and tosyl lysine chloromethyl ketone shows a similarity to trypsins and lack of inhibition by tosyl phenylalanine chloromethyl ketone indicates that acrosin is not chymotrypsin-like. The enzyme is also inhibited by soybean trypsin inhibitor. Acrosin appears to be a unique proteolytic enzyme and therefore deserves a specific name.