Regulation of spinach chloroplast coupling factor 1 ATPase activity

Illumination of chloroplast thylakoid membranes results in the activation of the light-triggered ATPase (coupling factor 1) and in exchange of tightly bound adenine nucleotides. The dark decay of the light-triggered ATPase activity is accelerated significantly by the addition of ADP. Both the decay of the ATPase activity and the rebinding of ADP appear to be rate limited by the same unimolecular step which is estimated to have a rate constant of 0.058 +/- 0.005 s-1. ADP is a noncompetitive inhibitor of the ATPase, if sufficient time for binding is allowed. The Kis for ADP inhibition of the ATPase is equivalent to the K0.5 for ADP binding to the nucleotide tight binding site (K0.5 = 2 +/- 1 microM). A kinetic model is proposed which suggests that the binding of one ADP to chloroplast coupling factor 1 inhibits three ATPase active sites.