Respiratory Na+ pump and Na+-dependent energetics inVibrio alginolyticus

The marine bacteriumVibrio alginolyticus was found to possess the respiratory Na⁺ pump that generates an electrochemical potential of Na⁺, which plays a central role in bioenergetics ofV. alginolyticus, as a direct result of respiration. Mutants defective in the Na⁺ pump revealed that one of the two kinds of NADH: quinone oxidoreductase requires Na⁺ for activity and functions as the Na⁺ pump. The Na⁺ pump composed of three subunits was purified and reconstituted into liposomes. Generation of membrane potential by the reconstituted proteoliposomes required Na⁺. The respiratory Na⁺ pump coupled to the NADH: quinone oxidoreductase was found in wide varieties of Gramnegative marine bacteria belonging to the generaAlcaligenes, Alteromonas, andVibrio, and showed a striking similarity in the mode of electron transfer and enzymic properties. Na⁺ extrusion seemed to be coupled to a dismutation reaction, which leads to the formation of quinol and quinone from semi-quinone radical.