DeltamuH(+) is known to stimulate the enzyme activity of chloroplast ATP synthase in addition to its important role as energy supply for ATP synthesis. In the present study, we focused on the relationship between the proton translocation via the membrane sector of ATP synthase, F., and the conformational change of the central stalk subunit gamma. The conformational change of CF1 mainly at the gamma subunit was induced by the proton flow via F-0 in the absence of substrates. The effects of inhibitors on CF0 or CF1 for this conformational change were also examined. The observed conformational change was partially suppressed by ADP binding. From these results, we propose the DeltamuH(+)-dependent conformational change of CF1 on the enzyme activation process, which is affected by both ADP binding to the catalytic sites and proton flow via F-0 portion. (C) 2003 Elsevier Science (USA). All rights reserved.