Phosphorylation and dephosphorylation of Mg2+-independent Ca2+-ATPase from goat spermatozoa

We reported previously that a Ca2+-ATPase in rat testes and goat spermatozoa could be activated by Ca2+ alone without Mg2+, though it has a lot of similarities with the well known Ca2+, Mg2+-ATPase. Recently, we were successful in isolating the phosphorylated intermediate of the former enzyme under control conditions i.e., in the presence of low concentration of Ca2+ and at low temperature. Increase of the concentration of Ca2+ and/or temperature lead to dephosphorylation. Based on our observations, we proposed a reaction scheme comparable to that of Ca2+, Mg2+-ATPase. The findings strengthened our previous report that Mg2+-independent Ca2+-ATPase is involved in Ca2+ transport and Ca2+ uptake like Ca2+, Mg2+-ATPase.