Sperm phospholipid methyltransferase activity during preparation for exocytosis

The present report describes experiments to evaluate phospholipid methyltransferase activity in golden hamster spermatozoa incubated under different conditions. Washed cauda epididymal sperm were incubated with taurine, in the presence or absence of epinephrine. At various times, the sperm were separated, and phospholipid methyltransferase activity measured. Also, at each time, aliquots of the sperm suspension were assayed for motility, and acrosome reactions. Some sperm incubated in the presence of taurine and epinephrine were capacitated by 3.5 h, because about 40 per cent of them can undergo the acrosome reaction 10 min after addition of the fusogen lysophosphatidylcholine. In epinephrine-free incubations the fusogen failed to stimulate acrosome reactions. On the other hand, epinephrine stimulated by twofold phospholipid methyltransferase activity from '0 time' incubated sperm, in comparison to that observed in taurine-treated cells. Enzyme activities from both taurine or epinephrine plus taurine-treated cells decreased as the incubation time of the sperm suspension increased. Kinetic properties of the sperm phospholipid methyltransferase activity were modified by the presence of taurine and epinephrine when S-adenosylmethionine was used as the substrate. These results suggest that refined molecular events occur in the sperm cell during the acquisition of fertilizing ability.