Respiratory Na+ pump and Na+-dependent energetics in Vibrio alginolyticus.
The marine bacterium Vibrio alginolyticus was found to possess the respiratory Na+ pump that generates an electrochemical potential of Na+, which plays a central role in bioenergetics of V. 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 Gram-negative marine bacteria belonging to the genera Alcaligenes, Alteromonas, and Vibrio, 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 semiquinone radical.