Na(+) translocation by bacterial NADH:quinone oxidoreductases: an extension to the complex-I family of primary redox pumps.
The current knowledge on the Na(+)-translocating NADH:ubiquinone oxidoreductase of the Na(+)-NQR type from Vibrio alginolyticus, and on Na(+) transport by the electrogenic NADH:Q oxidoreductases from Escherichia coli and Klebsiella pneumoniae (complex I, or NDH-I) is summarized. A general mode of redox-linked Na(+) transport by NADH:Q oxidoreductases is proposed that is based on the electrostatic attraction of a positively charged Na(+) towards a negatively charged, enzyme-bound ubisemiquinone anion in a medium of low dielectricity. A structural model of the [2Fe-2S]- and FAD-carrying NqrF subunit of the Na(+)-NQR from V. alginolyticus based on ferredoxin and ferredoxin:NADP(+) oxidoreductase suggests that a direct participation of the Fe/S center in Na(+) transport is rather unlikely. A ubisemiquinone-dependent mechanism of Na(+) translocation is proposed that results in the transport of two Na(+) ions per two electrons transferred. Whereas this stoichiometry of the pump is in accordance with in vivo determinations of Na(+) transport by the respiratory chain of V. alginolyticus, higher (Na(+) or H(+)) transport stoichiometries are expected for complex I, suggesting the presence of a second coupling site.
Mikrobiologisches Institut der Eidgenössischen Technischen Hochschule, ETH-Zentrum, Schmelzbergstr. 7, CH-8092, Zürich, Switzerland. fritz-steuber@micro.biol.ethz.ch
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Steuber
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D002414:Cations, Monovalent; D003593:Cytoplasm / Q000378:metabolism; D042967:Electron Transport Complex I; D004926:Escherichia coli / Q000201:enzymology*; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D019897:Periplasm / Q000378:metabolism; D011808:Quinone Reductases / Q000378:metabolism*; D016415:Sequence Alignment; D012964:Sodium / Q000378:metabolism*; D014733:Vibrio / Q000201:enzymology*
D001426:Bacterial Proteins; D002414:Cations, Monovalent; D012964:Sodium; D009247:NADH, NADPH Oxidoreductases; C084142:sodium-translocating NADH-quinone reductase; D011808:Quinone Reductases; D042967:Electron Transport Complex I