title: Properties of respiratory chain-linked Na(+)-independent NADH-quinone reductase in a marine Vibrio alginolyticus.
abstract: The respiratory chain of a marine Vibrio alginolyticus contains two types of NADH-quinone reductase (NQR): one is an Na(+)-dependent NQR functioning as an Na+ pump (NQR-1) and the other is an Na(+)-independent NQR (NQR-2). NQR-2 was purified about 55-fold from the membrane of mutant Nap-1 which is devoid of NQR-1, and its properties were compared with those of NQR-1. In contrast to NQR-1, the purified NQR-2 does not require any salts for activity and is not inhibited by up to 0.4 M salts. The optimum pH of NQR-2 is between 6.8 and 7.8, which is about 0.7 ph units lower than that of NQR-1. NQR-2 is insensitive to strong inhibitors of NQR-1 such as p-chloromercuribenzoate, Ag+ and 2-heptyl-4-hydroxyquinoline N-oxide. Using inverted membrane vesicles, it was confirmed that NQR-2 has no capacity to generate a membrane potential. NQR-2 reduces menadione and ubiquinone-1 by a two-electron reduction pathway. Since the NADH-reacting FAD-containing beta-subunit of NQR-1 reduces quinones by a one-electron reduction pathway, the mode of quinone reduction is closely related to energy coupling; the formation of semiquinone radicals as an intermediate is likely to be essential to functioning as an ion pump.
authors.affiliation: Laboratory of Membrane Biochemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Hayashi
authors.forename: T
authors.initials: T
authors.lastname: Miyoshi
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Unemoto
mesh_terms: D042963:Electron Transport Complex II; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000302:isolation & purification; D007700:Kinetics; D008564:Membrane Potentials; D009097:Multienzyme Complexes / Q000302:isolation & purification; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification*; D010088:Oxidoreductases / Q000302:isolation & purification; D013385:Succinate Dehydrogenase / Q000302:isolation & purification; D014733:Vibrio / Q000201:enzymology*
chemical_list: D007527:Isoenzymes; D009097:Multienzyme Complexes; D010088:Oxidoreductases; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; D016660:NAD(P)H Dehydrogenase (Quinone)