Upon EDTA treatment thylakoids lose the chloroplast coupling factor 1 (CF1) part of their ATP synthase, CFoCF1, this exposes the proton channel, CFo. The previously established ability of the CF1 subunit δ to block the proton leak through CFo prompted us to study (a) the ability of complete CF1 and, for comparison, CF1 lacking the δ subunit to block proton leakage and thereby to reconstitute structurally some photophosphorylation activity of the remaining CFoCF1 molecules and (b) their ability to form functional enzymes (functional reconstitution). In order to discriminate between activities caused by added CF1 or CF1 (−δ) and remaining CFoCF1, the former were inhibited by chemical modification of subunit β by N,N′‐dicyclohexyl carbodiimide (DCCD) and the latter by tentoxin. We found that added CF1 acted both structurally and functionally while added DCCD‐treated CF1 (DCCD‐CF1) acted only structurally. In contrast to previous observations, CF1(−δ) and DCCD‐CF1(−δ) also acted structurally although the reduction of proton leakage was smaller than with DCCD‐CF1. Hence there was no functional reconstitution without subunit δ present. Previous studies indicated that only a small fraction of exposed CFo is highly conducting and that this small fraction is distinguished by its high affinity for added CF1. The results of this study point rather to a wider distribution of CFo conductance states and binding affinities. Copyright © 1990, Wiley Blackwell. All rights reserved
