Abstract
Thiol modulation of the chloroplast ATP synthase γ subunit has been recognized as a important regulation system to activate the enzyme activity under the preferable photosynthetic conditions in the daytime Based on this concept, the biochemical property of the reduced form ATP synthase was studied, and Junesch and Graeber found that the membrane potential required to initiate ATP synthesis for the reduced enzyme was lower than that for the oxidized enzyme (Biochim. Biophys. Acta (1987) 893: 275-288). However, it is still very unclear how and when the chloroplast ATP synthase is reduced and oxidized in nature. From the thorough analysis of the redox conditions of regulatory cysteines of the γ subunit of the chloroplast ATP synthase in spinach leaves, the significance of thiol modulation of this enzyme was clarified as for the shut down of the futile ATP hydrolysis activity in the dark but not for the efficient ATP synthesis in the light. Significance of the membrane potential to reduce the γ subunit under the physiological conditions was clarified as well.
