Characterization of Mg2+- and Ca2+-ATPase activity in membrane vesicles from ejaculated ram seminal plasma

The activity of divalent cation-stimulated adenosine triphosphatase (ATPase) has been studied in vesicular membranes isolated from ejaculated ram seminal plasma. This nonspecific acidic ATPase can be activated by millimolar concentration of any one of the following cations: Ca2+, Mg2+, Zn2+, or Mn2+ to give high specific activity (approximately 300 mumol/mg/hr), in absence of the other cations. Free Zn2+ inhibits activity of this ATPase. The Km for adenosonine triphosphate (ATP) ranged between 0.17 and 0.24 mM, and for the divalent cation ranged between 0.4 and 0.8 mM. When the ATPase is activated by Ca2+, two Kms for Ca2+ concentration were found: 0.8 and 0.08 mM. It is suggested that the seminal plasma membranes also contain alkaline ATPase, which is more specific for Ca2+.