Gossypol Inhibition of Acrosin and Proacrosin, and Oocyte Penetration by Human Spermatozoa

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Abstract
Gossypol, a known antispermatogenic agent, effectively inhibited the highly purified boar sperm proacrosin-acrosin proteinase enzyme system by irreversibly preventing the autoproteolytic conversion of proacrosin to acrosin and reversibly inhibiting acrosin activity. The agent appears to prevent the self-catalyzed by not the acrosin-catalyzed activation of proacrosin. Brief exposure of human semen to concentrations of gossypol, which did not visibly alter spermatozoal motility or forward progression, irreversibly inhibited the conversion of proacrosin to acrosin although the activity of the nonzymogen acrosin was not decreased; this prevented the human spermatozoa from penetrating denuded hamster oocytes. Gossypol inhibition of proacrosin conversion to acrosin closely paralleled the decline in oocyte penetration. Racemic (.+-.) gossypol was equally as effective as the enantiomer (+) gossypol. The inhibition of proacrosin conversion to acrosin is a mechanism by which gossypol could exert its antifertility effect at nonspermicidal concentrations. Low levels of gossypol should be tested for their contraceptive action when placed vaginally.