RECONSTITUTION OF PHOTOPHOSPHORYLATION WITH COUPLING FACTOR-I ATPASES FROM THE THERMOPHILIC BACTERIUM PS3 AND LETTUCE CHLOROPLASTS

EDTA-resolved particles (partially depleted of coupling factor 1) from lettuce chloroplast thylakoids (CF1) were reconstituted with CF1 from lettuce and with coupling factor 1 from the thermophilic bacterium PS3 (TF1). The binding affinity of both F1 proteins for the membranal CF0 (chloroplast F0) is similar. The phosphorylation activities of the EDTA-resolved particles after reconstitution with either the tentoxin-sensitive CF1 or the tentoxin-resistant TF1 are equally inhibited by tentoxin. The same degree of reconstitution of photophosphorylation is observed either with the native TF1, the DCCD[dicyclohexylcarbodiimide]-modified TF1 or the DCCD-modified CF1. Particles reconstituted with native CF1 always catalyzed a higher rate of ATP formation. NaBr-resolved particles (CF1-depleted) bind TF1 with the reconstitution of the light-dependent H+ uptake. However, no significant enhancement of ATP formation accompanies the binding of TF1 to the membranal CF0. These findings suggest a close relationship between the F0-F1 complex of the prokaryotic thermophilic bacterium PS3 and that from lettuce, a eukaryotic organism. It is also apparent that the rebinding of added TF1 or CF1 to CF1-depleted particles reforms ATP synthetase complexes that are fully catalytically functional. The TF1 incorporated into the membrane appears to have only a structural role of sealing the membrane and preventing protons from leaking out but does not participate in the catalytic process itself. The endogenous CF1 that is present in the native undissociated ATP synthetase complex and still remains in these CF1-partially depleted membranes is the catalytically active enzyme species.