Vanadate inhibition of the Ca2+-ATPase from human red cell membranes.

(1) VO3(-) combines with high affinity to the Ca2+-ATPase and fully inhibits Ca2+-ATPase and Ca2+-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state of the Ca2+-dependent phosphoenzyme. (2) VO3(-) blocks hydrolysis of ATP at the catalytic site. The sites for VO3(-) also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca2+-ATPase. (3) The sites for VO39-) show positive interaactions in affinity with sites for Mg2+ and K+. This accounts for the dependence on Mg2+ and K+ of the inhibition by VO3(-). Although, with less effectiveness, Na2+ and K+ substitutes for K+ whereas Li+ does not. The apparent affinites for Mg24 and K+ for inhibiton by VO3(-) seem to be less than those for activation of the Ca2+-ATPase. (4) Inhibition by VO3(-) is independent of Ca2+ at concentrations up to 50 microM. Higher concentrations of Ca2+ lead to a progressive release of the inhibitiory effect of VO3(-).