Regulation of plasma membrane H+-ATPase from corn-root by Mg2+ and pH.

The plasma membrane H+-ATPase of corn-root is activated by free Mg2+ at pH 6.0 (Ks = 2.9 mM) but not at pH 7.0. As a result, the pH dependence of the enzyme varies depending on the Mg2+ concentration of the medium. The activation by Mg2+ is promoted by an increase in Vmax with no effect on the apparent Km for Mg.ATP. Different from Mg2+, free Mn2+, Co2+, and Ni2+ do not activate at pH 6.0 and inhibit the H+-ATPase at pH 7.0. The effects of divalent cations on the corn ATPase observed in this report are different from those previously described for the yeast enzyme (Brooker, R.J. and Slayman, C.W. (1983) J. Biol. Chem. 258, 8833-8838), suggesting different mechanisms of regulation for the isoforms of yeast and corn H+-ATPase.