Gastricsin‐Mediated Proteolytic Degradation of Human Seminal Fluid Proteins at pH Levels Found in the Human Vagina

The proteolytic degradation of human seminal fluid proteins at acidic conditions has been investigated. Upon acidification to the pH level of the human vagina, autoproteolysis of most seminal fluid proteins occurred after 30 minute of incubation at 37°C. The degradation was unaffected by inhibitors of serine, thiol, or me‐tallo proteases, whereas pepstatin prevented any proteolysis. The proteins in seminal fluid depleted of the aspartic protease progastricsin did not degrade upon acidification. Readdition of the progastricsin restored the autoproteolytic ability of seminal fluid. Prostate‐specific antigen, prostatic acid phosphatase, and Zn‐α₂‐glycoprotein are quickly degraded; albumin, transferrin, and lactoferrin are degraded more slowly. The low molecular weight fragments of semenogelin I and II and especially β‐microseminoprotein are somewhat resistant to proteolysis. These observations strongly suggest that the aspartic protease progastricsin is responsible for the autoproteolysis of seminal fluid proteins under acidic conditions. This suggests that the function of the enzyme is to degrade seminal fluid proteins deposited in the vagina; this in turn may decrease the antigenic load in the vagina and prevent immuno‐infertility. 1993 American Society of Andrology