Changes in activity and structure of the chloroplast proton ATPase induced by illumination of spinach leaves

Abstract

Photophosphorylating activity of chloroplasts rapidly prepared from preilluminated spinach leaves was higher than the activity of chlorplasts from leaves kept in the dark. Higher Vmax values were obtained with the former when either ADP or Pi concentrations were varied. The rate of decay of the in vivo light-activated Mg2+-ATPase was highly dependent on temperature, increasing with it. At 0 degree C it was stable for 40 min or more. The decay at 25 degrees C was prevented by 5 mM ATP or 50 mM dithioerythritol while ADP or Pi did not affect it. Gramicidin or iodosobenzoate induced a very rapid decay even at 0 degree C. Coupling factor 1 with a manifest and stable Ca2+-ATPase activity was solubilized from chloroplasts activated by light in vivo. Incubation of chloroplasts from preilluminated leaves with N-[3H]ethylmaleimide resulted in an inhibition of Ca2+-ATPase activity and in the incorporation of radioactivity into the gamma subunit of coupling factor 1 that was larger than that of chloroplasts from leaves kept in the dark. The results show that activation in vivo of the proton ATPase was manifested by higher phosphorylating and Mg2+-ATPase activities and requires both an electrochemical proton gradient and a redox change of at least one disulfide bond of its gamma subunit.