The Biological Role of the ζ Subunit as Unidirectional Inhibitor of the F 1 F O -ATPase of Paracoccus denitrificans.

The biological roles of the three natural F1 FO -ATPase inhibitors, ε, ζ, and IF1 , on cell physiology remain controversial. The ζ subunit is a useful model for deletion studies since it mimics mitochondrial IF1 , but in the F1 FO -ATPase of Paracoccus denitrificans (PdF1 FO ), it is a monogenic and supernumerary subunit. Here, we constructed a P. denitrificans 1222 derivative (PdΔζ) with a deleted ζ gene to determine its role in cell growth and bioenergetics. The results show that the lack of ζ in vivo strongly restricts respiratory P. denitrificans growth, and this is restored by complementation in trans with an exogenous ζ gene. Removal of ζ increased the coupled PdF1 FO -ATPase activity without affecting the PdF1 FO -ATP synthase turnover, and the latter was not affected at all by ζ reconstitution in vitro. Therefore, ζ works as a unidirectional pawl-ratchet inhibitor of the PdF1 FO -ATPase nanomotor favoring the ATP synthase turnover to improve respiratory cell growth and bioenergetics.