Vanadate inhibition of brain (Ca + Mg)-ATPase.

Vanadate was a potent inhibitor of the membrane-bound (Ca + Mg)-ATPase from rat brain, the concentration required for 50% inhibition under conditions optimal for enzymatic activity being 3 mu M. Vanadate inhibition increased with the MgCl2 concentration, half-maximal inhibition occurring at 2 mM MgCl2, near the MgCl2 concentration required for half-maximal activation of the ATPase activity. MnCl2 could substitute for MgCl2, and at concentrations of 1 mM (Ca + Mn)-ATPase activity was greater than (Ca + Mg)-ATPase activity, although sensitivity to vanadate was less. Vanadate inhibition increased also with the KCl concentration, half-maximal inhibition occurring at 8 mM, again near the concentration required for half-maximal activation of ATPase activity. By contrast, NaCl stimulated (Ca + Mg)-ATPase activity without potentiating vanadate inhibition. These effects of cations on ATPase activity and vanadate inhibition resemble properties of certain transport ATPases and thus suggest mechanistic and functional similarities.