Reconstitution of photophosphorylation in EDTA‐treated thylakoids by added chloroplast coupling factor 1 (ATPase) and chloroplast coupling factor 1 lacking the δ subunit

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