Proton gradient across the chloroplast thylakoid membrane governs the redox regulatory function of ATP synthase
Takatoshi Sekiguchi, Keisuke Yoshida, Ken‐ichi Wakabayashi, Toru Hisabori
Abstract
Chloroplast ATP synthase (CF o CF 1 ) synthesizes ATP by using a proton electrochemical gradient across the thylakoid membrane, termed Δ μ H + , as an energy source. This gradient is necessary not only for ATP synthesis but also for reductive activation of CF o CF 1 by thioredoxin, using reducing equivalents produced by the photosynthetic electron transport chain. Δ μ H + comprises two thermodynamic components: pH differences across the membrane (ΔpH) and the transmembrane electrical potential (ΔΨ). In chloroplasts, the ratio of these two components in Δ μ H + is crucial for efficient solar energy utilization. However, the specific contribution of each component to the reductive activation of CF o CF 1 remains unclear. In this study, an in vitro assay system for evaluating thioredoxin-mediated CF o CF 1 reduction is established, allowing manipulation of Δ μ H + components in isolated thylakoid membranes using specific chemicals. Our biochemical analyses revealed that ΔpH formation is essential for thioredoxin-mediated CF o CF 1 reduction on the thylakoid membrane, whereas ΔΨ formation is nonessential.