Proton-Translocating ATP-Synthase of Paracoccus denitrificans: ATP-Hydrolytic Activity

Tightly coupled membranes of Paracoccus denitrificans catalyze oxidative phosphorylation but are incapable of ATP hydrolysis. The conditions for observation and registration of the venturicidin-sensitive ATPase activity of subbacterial particles derived from this organism are described. The ATP hydrolytic activity does not appear after prolonged incubation in the presence of pyruvate kinase and phosphoenol pyruvate (to remove ADP), EDTA (to remove Mg²⁺) and/or inorganic phosphate, whereas the activity dramatically increases after energization of the membranes. ATP hydrolysis byactivated ATPase is coupled with electric potential formation. Inorganic phosphate prevents and azide promotes a decline of the enzyme activity during ATP hydrolysis. The addition of uncouplers results in rapid and complete inactivation of ATPase. The dependent ATPase activity increases upon dilution of the membranes. The results are discussed as evidence for the presence of distinct ATP-synthase and ATP-hydrolase states of F_oF₁ complex in the coupling membranes (Vinogradov, A. D. (1999) Biochemistry (Moscow), 64, 1219-1229). The proposal is made that part of the free energy released from oxidoreduction in the respiratory chain is used to maintain active conformation of the energy-transducing proteins.