Abstract
Protein carboxylmethylase (S-adenosyl-L-methionine:protein O-methyltransferase, EC 2.1.1.24.) is believed to be involved in the regulation of sperm motility. To test this hypothesis, we investigated the effects of erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA) which, in combination with adenosine and homocysteine thiolactone, inhibits protein carboxylmethylase activity in monocytes. This group of compounds inhibited sea urchin sperm motility. Unexpectedly, EHNA alone inhibited the motility., This observation was confirmed in intact spermatozoa from rats, rabbits, and humans. EHNA also inhibited the motility of demembranated, reactivated sea urchin and rat spermatozoa from which protein carboxylmethylase had been extracted. In these preparations, motility was restored by ATP. These observations suggested that EHNA arrests sperm motility by inhibiting the axonemal dynein ATPase on which motility depends. Kinetic analysis demonstrated that EHNA produced mixed inhibition of both the axonemal ATPase and the partially purified dynein 1 from sea urchin sperm tails, as well as the axonemal ATPase of rat sperm tails. These observations also provide evidence for the similarity of the active site of the dynein ATPase in sea urchin and rat spermatozoa.
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