title: Na+ is translocated at NADH:quinone oxidoreductase segment in the respiratory chain of Vibrio alginolyticus.
abstract: The coupling site of the Na+ pump to the respiratory chain of Vibrio alginolyticus was examined using membrane fractions prepared from the wild type, Na+ pump-deficient mutants, and spontaneous revertant. NADH oxidase of the wild type and revertant specifically required NA+ for maximum activity, whereas Na+ was not essential for the NADH oxidase of mutants. Similar to the Na+ pump in whole cells, the Na+-dependent NADH oxidase in membranes had a pH optimum in the alkaline region. A respiratory inhibitor, 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), inhibited the Na+-dependent NADH oxidase but had little effect on the NA+-independent activity of mutant membranes. NADH:quinone oxidoreductase was found to be the Na+-dependent HQNO-sensitive site of the NADH oxidase. In the wild type cells, HQNO was also found to cause a strong inhibition of the Na+ pump with little effect on the overall H+ extrusion by respiration. The inhibition of the Na+ pump by HQNO was overcome by oxidized, but not reduced, N,N,N',N'-tetra-methyl-p-phenylenediamine (TMPD). In the presence of oxidised TMPD, the electron flow NADH to oxygen seemed to bypass the HQNO-sensitive site and energize the Na+ pump. From these results, it was concluded that the Na+ pump is coupled to the respiratory chain at the step of NADH:quinone oxidoreductase.
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D006912:Hydroxyquinolines / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010101:Oxygen Consumption; D011808:Quinone Reductases / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013772:Tetramethylphenylenediamine / Q000494:pharmacology; D014733:Vibrio / Q000201:enzymology*
chemical_list: D006912:Hydroxyquinolines; D009097:Multienzyme Complexes; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D012964:Sodium; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases; D013772:Tetramethylphenylenediamine; D001205:Ascorbic Acid