Proteinase Inhibitors and Proteinases of Human Semen
During the First International Research Conference on Proteinase Inhibitors, a survey was presented concerning the proteinases of spermatozoa and seminal plasma as was known until that time [1, 2]. In summary, a proteinase from rabbit spermatozoa was purified and characterized, and shown to differ from other known pro-teolytic enzymes. It was given the name “Acrosin” (approved by the Commission on Enzyme Nomenclature), alternately being called “Acrosomal Proteinase” by some authors. Acrosin was thought to be associated with the acrosome, a sac-like structure that caps the anterior portion of the sperm head. This has recently been confirmed by various authors [3, 4, 5]. Acrosin removes the zona pellucida of the rabbit ovum and is apparently used by the spermatozoon to penetrate this layer during the fertilization process. In certain species, such as the rabbit, boar and stallion [1, 6], acrosin activity is high in extracts from epididymal spermatozoa and low in extracts from ejaculated spermatozoa. This is due to the addition of one or more proteinase inhibitors from seminal plasma to the sperm during ejaculation. In various other species, such as the bull and rodents, epididymal spermatozoa possess high levels of inhibitor already, depressing the activity of acrosin. The epididymal inhibitor probably originates from the rete testis . Its concentration in boar epididymal fluid is much lower than in boar seminal plasma, explaining the difference in acrosin activity of epididymal and ejaculated sperm in this species. The ram does not show these differences  and indeed the epididymal plasma and seminal plasma possess approximately the same concentration of inhibitor . The molecular weight of the rete testis inhibitor was estimated as 6500 , identical to the inhibitor in seminal plasma . Whether these inhibitors are the same remains to be established, however.
KeywordsSeminal Plasma Zona Pellucida Sperm Head Epididymal Spermatozoon Human Semen
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