Inhibition of thermophilic F1-ATPase by the ε subunit takes different path from the ADP-Mg inhibition.

The F1-ATPase, the soluble part of FoF1-ATP synthase, is a rotary molecular motor consisting of α3β3γδe. The γ and e subunits rotate relative to the α3β3δ sub-complex on ATP hydrolysis by the β subunit. The e subunit is known as an endogenous inhibitor of the ATPase activity of the F1-ATPase and is believed to function as a regulator of the ATP synthase. This inhibition by the e subunit (e inhibition) of F1-ATPase from thermophilic Bacillus PS3 was analyzed by single molecule measurements. By using a mutant e subunit deficient in ATP binding, reversible transitions between active and inactive states were observed. Analysis of pause and rotation durations showed that the e inhibition takes a different path from the ADP-Mg inhibition. Furthermore, the addition of the mutant e subunit to the α3β3γ sub-complex was found to facilitate recovery of the ATPase activity from the ADP-Mg inhibition. Thus, it was concluded that these two inhibitions are essentially exclusive of each other.