Effect of modulators on prostasome membrane-bound ATPase in human seminal plasma

The Mg2+- and Ca2+-dependent ATPase system in human seminal fluid is linked to membranes encasing small organelles denoted 'prostasomes'. This activity was completely pelleted after ultracentrifugation at 105,000 X g, provided the seminal plasma was diluted 1:10. On the contrary, prostatic acid phosphatase activity remained in the supernatant and was inhibited to about 75% by tartrate (0.5 mmol l-1) contrasting with the ATPase system that was not inhibited. Calmodulin, in the concentration interval 0.30-0.90 mumol l-1, did not further activate the ATPase system. Calmidazolium, which is a highly lipophilic substance, was a competitive inhibitor of the Mg2+- and Ca2+-dependent ATPase and half maximal inhibition was attained at 2-3 mumol l-1 calmidazolium. This inhibition was antagonized to a moderate degree (25%, P less than 0.02) by calmodulin, 0.60 mumol l-1. Quercetin, at concentrations of 30-60 mumol l-1, did not influence the prostasome membrane ATPase in any direction. Oleate was an inhibitor of the ATPase system at any concentration up to 50 mumol l-1. This inhibition was not counteracted to an appreciable extent by calmodulin. These results displayed a pattern giving support to the view that the Mg2+- and Ca2+-dependent ATPase of the prostasome membrane may be the molecular basis for vectorial transport of Ca2+ into prostasomes.