The effect of energization and of thiol modulation on ATP hydrolysis by soluble and membrane-bound chloroplast coupling factor

AbstractThe effects of energization and of thiol modulation on ATPase activity of chloroplast coupling factor 1 are described. At 64°C the enzyme hydrolyses ATP both with Mg or Ca ions and is insensitive to thiol modulation. Cooling down to 37°C converts the enzyme to a modulation-sensitive, Ca-specific ATPase. Mg-ATPase activity of chloroplasts is only slightly stimulated by thiol modulation when measured during illumination, yet, the presence of thiol reducing agents in the light largely stimulates ATPase activity in the subsequent dark period. It is suggested that the enzyme exists in two different catalytically active states: (1) energized state, insensitive to thiol-modulation, and (2) deenergized state, stimulated by thiolmodulation