Oxytocinase Activity in Human Spermatozoa and Its Possible Role in Fertilization

Abstract

Human spermatozoa were extracted with 1% Triton X-100 and analyzed for oxytocinase (E.C. 3.4.11.3) activity by means of two synthetic peptides, S-benzyl-L-cysteine-p-nitroanilide (BCN) and L-leucine-p-nitroanilide (LN), separately as substrates. The specific activity (mean ± SD) of this proteolytic enzyme at Vmax in eight different extracts was 0.150 ± 0.072 and 1.392 ± 0.602 mIU/10⁶ cells using BCN and LN, respectively. The enzyme showed optimal activity at pH 7.2 when BCN was the substrate, and at pH 7.4 with LN as the substrate. Spermatozoal oxytocinase activity may be involved directly or indirectly in the reproductive mechanisms leading to sperm acrosome reaction and fertilization.

Key Words:

• Spermatozoa
• Oxytocinase
• Cystine aminopeptidase
• Acrosome reaction
• Fertilization
• Triton X-100
• Oxytocin
• Vasopressin
• Met-enkephalin