Na+ translocation by bacterial NADH:quinone oxidoreductases: an extension to the complex-I family of primary redox pumps11Dedicated to Peter Dimroth on the occasion of his 60th birthday.

AbstractThe 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