title: Na(+)-translocating NADH-quinone reductase of marine and halophilic bacteria.
abstract: The respiratory chain of marine and moderately halophilic bacteria requires Na+ for maximum activity, and the site of Na(+)-dependent activation is located in the NADH-quinone reductase segment. The Na(+)-dependent NADH-quinone reductase purified from marine bacterium Vibrio alginolyticus is composed of three subunits, alpha, beta, and gamma, with apparent M(r) of 52, 46, and 32 kDa, respectively. The FAD-containing beta-subunit reacts with NADH and reduces ubiquinone-1 (Q-1) by a one-electron transfer pathway to produce ubisemiquinones. In the presence of the FMN-containing alpha-subunit and the gamma-subunit, Q-1 is converted to ubiquinol-1 without the accumulation of free radicals. The reaction catalyzed by the alpha-subunit is strictly dependent on Na+ and is strongly inhibited by 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO), which is tightly coupled to the electrogenic extrusion of Na+. A similar type of Na(+)-translocating NADH-quinone reductase is widely distributed among marine and moderately halophilic bacteria. The respiratory chain of V. alginolyticus contains another NADH-quinone reductase which is Na+ independent and has no energy-transducing capacity. These two types of NADH-quinone reductase are quite different with respect to their mode of quinone reduction and their sensitivity toward NADH preincubation.
authors.affiliation: Laboratory of Membrane Biochemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Unemoto
authors.forename: M
authors.initials: M
authors.lastname: Hayashi
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004579:Electron Transport; D004734:Energy Metabolism; D005486:Flavin Mononucleotide / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000201:enzymology; D006217:Halobacterium / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D011487:Protein Conformation; D011808:Quinone Reductases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D013045:Species Specificity; D014451:Ubiquinone / Q000378:metabolism; D014733:Vibrio / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D009243:NAD; D014451:Ubiquinone; D005486:Flavin Mononucleotide; D012964:Sodium; D010088:Oxidoreductases; C020094:duroquinol oxidase; C084142:sodium-translocating NADH-quinone reductase; D016660:NAD(P)H Dehydrogenase (Quinone); D011808:Quinone Reductases; D009245:NADH Dehydrogenase