MALATE REGULATION OF MG2-ATPASE OF CHLOROPLAST COUPLING FACTOR-1()

The regulatory effects of malate on chloroplast Mg2+-ATPase were inves tigated and the mechanism was discussed. Malate stimulated methanol-ac tivated membrane-bound and isolated CF1 Mg2+-ATPase activity. The gamm a subunit of CF1 may be involved in malate regulation of the enzyme fu nction. Modification of gamma subunit at one site of the peptide by NE M may affect malate stimulation of ATPase while at another site may ha ve no effect. The effect of malate on the Mg2+-ATPase was also control led by the Mg2+/ATP ratio in the reaction medium. The enhancing effect of malate on Mg2+ -ATPase activity depended on the presence of high c oncentrations of Mg2+ in the reaction mixture. Kinetic study showed th at malate raised the V-max of catalysis without affecting the K-m for Mg(2+)ATP. The experiments imply that the stimulation of Mg2+-ATPase b y malate is probably correlated with the P-i binding site on the enzym e. The regulation of ATPase activity by malate in chloroplasts may be relevant to its function in vivo.