Generalized Distribution and Common Properties of Na+-dependent NADH: Quinone Oxidoreductases in Gram-negative Marine Bacteria

Abstract

Effects of Na+ on respiratory NADH oxidase were studied in membranes prepared from Gram-negative marine bacteria belonging to the genera Alcaligenes, Alteromonas, Flavobacterium and Vibrio. NADH oxidases of 9 out of the 10 strains examined were found to require Na+ for maximum activity. Without exception, the Na+-dependent site was located at the level of the NADH: quinone oxidoreductase region of the respiratory chain and was highly sensitive to 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO). NADH dehydrogenases in the Na+-dependent segment were sensitive to Ag+ and able to oxidize reduced nicotinamide hypoxanthine dinucleotide as a substrate. Since the NADH dehydrogenase was neither dependent on Na+ nor sensitive to HQNO, it was suggested that reduction of quinone by the NADH: quinone oxidoreductase involves the formation of an intermediate, presumably semiquinone, and that electron transfer from the intermediate requires Na+ and is sensitive to HQNO. These results showed a striking similarity to those obtained with the Na+-dependent NADH: quinone oxidoreductase, the Na+ pump, of Vibrio alginolyticus, indicating that this enzyme is widely distributed among Gram-negative marine bacteria and shares common properties.