ε Subunit, an endogenous inhibitor of bacterial F1-ATPase, also inhibits F0F1-ATPase

Since the report by Sternweis and Smith (Sternweis, P. C., and Smith, J. B. (1980) Biochemistry 19, 526-531), the epsilon subunit, an endogenous inhibitor of bacterial F-1-ATPase, has long been thought not to inhibit activity of the holo enzyme, F0F1-ATPase. However, we report here that the epsilon subunit is exerting inhibition in F0F1-ATPase. We prepared a C-terminal half-truncated epsilon subunit (epsilon(Delta C)) of the thermophilic Bacillus PS3 F0F1-ATPase and reconstituted F-1- and F0F1-ATPase containing epsilon(Delta C). Compared with F-1- and F0F1-ATPase containing intact epsilon, those containing epsilon(Delta C) showed uninhibited activity; severalfold higher rate of ATP hydrolysis at low ATP concentration and the start of ATP hydrolysis without an initial lag at high ATP concentration. The F0F1-ATPase containing epsilon(Delta C) was capable of ATP-driven H+ pumping. The time-course of pumping at low ATP concentration was faster than that by the F0F1-ATPase containing intact epsilon. Thus, the comparison with noninhibitory epsilon(Delta C) mutant shed light on the inhibitory role of the intact epsilon subunit in F0F1-ATPase.