The regulator of the F1 motor: inhibition of rotation of cyanobacterial F1-ATPase by the ɛ subunit

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Abstract
The chloroplast‐type F1 ATPase is the key enzyme of energy conversion in chloroplasts, and is regulated by the endogenous inhibitor ε, tightly bound ADP, the membrane potential and the redox state of the γ subunit. In order to understand the molecular mechanism of ε inhibition, we constructed an expression system for the α3β3γ subcomplex in thermophilic cyanobacteria allowing thorough investigation of ε inhibition. ε Inhibition was found to be ATP‐independent, and different to that observed for bacterial F1‐ATPase. The role of the additional region on the γ subunit of chloroplast‐type F1‐ATPase in ε inhibition was also determined. By single molecule rotation analysis, we succeeded in assigning the pausing angular position of γ in ε inhibition, which was found to be identical to that observed for ATP hydrolysis, product release and ADP inhibition, but distinctly different from the waiting position for ATP binding. These results suggest that the ε subunit of chloroplast‐type ATP synthase plays an important regulator for the rotary motor enzyme, thus preventing wasteful ATP hydrolysis.