Interaction of Venturicidin and F o ·F 1 -ATPase/ATP Synthase of Tightly Coupled Subbacterial Particles of Paracoccus denitrificans in Energized Membranes

Proton-translocating F o ∙F 1 -ATPase/synthase that catalyzes synthesis and hydrolysis of ATP is commonly considered to be a reversibly functioning complex. We have previously shown that venturicidin, a specific F o -directed inhibitor, blocks the synthesis and hydrolysis of ATP with a significant difference in the affinity [Zharova, T. V. and Vinogradov, A. D. (2017) Biochim. Biophys. Acta , 1858 , 939-944]. In this paper, we have studied in detail inhibition of F o ∙F 1 -ATPase/synthase by venturicidin in tightly coupled membranes of Paracoccus denitrificans under conditions of membrane potential generation. ATP hydrolysis was followed by the ATP-dependent succinate-supported NAD + reduction (potential-dependent reverse electron transfer) catalyzed by the respiratory chain complex I. It has been demonstrated that membrane energization did not affect the affinity of F o ∙F 1 -ATPase/synthase for venturicidin. The dependence of the residual ATP synthase activity on the concentration of venturicidin approximated a linear function, whereas the dependence of ATP hydrolysis was sigmoidal: at low inhibitor concentrations venturicidin strongly inhibited ATP synthesis without decrease in the rate of ATP hydrolysis. A model is proposed suggesting that ATP synthesis and ATP hydrolysis are catalyzed by two different forms of F o ∙F 1 .