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

The F-ATPase, the soluble part of FoF-ATP synthase, is a rotary molecular motor consisting of αβγδε. The γ and ε subunits rotate relative to the αβδ sub-complex on ATP hydrolysis by the β subunit. The ε subunit is known as an endogenous inhibitor of the ATPase activity of the F-ATPase and is believed to function as a regulator of the ATP synthase. This inhibition by the ε subunit (ε inhibition) of F-ATPase from thermophilic PS3 was analyzed by single molecule measurements. By using a mutant ε subunit deficient in ATP binding, reversible transitions between active and inactive states were observed. Analysis of pause and rotation durations showed that the ε inhibition takes a different path from the ADP-Mg inhibition. Furthermore, the addition of the mutant ε subunit to the αβγ 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.