Malate regulation of Mg(2+)-ATPase of chloroplast coupling factor 1.

The regulatory effects of malate on chloroplast Mg(2+)-ATPase were investigated and the mechanism was discussed. Malate stimulated methanol-activated membrane-bound and isolated CF1 Mg(2+)-ATPase activity. The γ subunit of CF1 may be involved in malate regulation of the enzyme function. Modification of γ subunit at one site of the peptide by NEM may affect malate stimulation of ATPase while at another site may have no effect. The effect of malate on the Mg(2+)-ATPase was also controlled by the Mg(2+)/ATP ratio in the reaction medium. The enhancing effect of malate on Mg(2+)-ATPase activity depended on the presence of high concentrations of Mg(2+) in the reaction mixture. Kinetic study showed that malate raised the Vmax of catalysis without affecting the Km for Mg(2+) ATP. The experiments imply that the stimulation of Mg(2+)-ATPase by malate is probably correlated with the Pi binding site on the enzyme. The regulation of ATPase activity by malate in chloroplasts may be relevant to its function in vivo.