title: Primary steps of the Na+-translocating NADH:ubiquinone oxidoreductase catalytic cycle resolved by the ultrafast freeze-quench approach.
abstract: The Na(+)-translocating NADH:ubiquinone oxidoreductase (Na(+)-NQR) is a component of respiratory chain of various bacteria, and it generates a redox-driven transmembrane electrochemical Na(+) potential. Primary steps of the catalytic cycle of Na(+)-NQR from Vibrio harveyi were followed by the ultrafast freeze-quench approach in combination with conventional stopped-flow technique. The obtained sequence of events includes NADH binding ( approximately 1.5 x 10(7) m(-1) s(-1)), hydride ion transfer from NADH to FAD ( approximately 3.5 x 10(3) s(-1)), and partial electron separation and formation of equivalent fractions of reduced 2Fe-2S cluster and neutral semiquinone of FAD ( approximately 0.97 x 10(3) s(-1)). In the last step, a quasi-equilibrium is approached between the two states of FAD: two-electron reduced (50%) and one-electron reduced (the other 50%) species. The latter, neutral semiquinone of FAD, shares the second electron with the 2Fe-2S center. The transient midpoint redox potentials for the cofactors obtained during the fast kinetics measurements are very different from ones achieved during equilibrium redox titration and show that the functional states of the enzyme realized during its turning over cannot be modeled by the equilibrium approach.
authors.affiliation: Department of Molecular Energetics of Microorganisms, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Bogachev
authors.forename: Nikolai P
authors.initials: NP
authors.lastname: Belevich
authors.forename: Yulia V
authors.initials: YV
authors.lastname: Bertsova
authors.forename: Michael I
authors.initials: MI
authors.lastname: Verkhovsky
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005615:Freezing; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D016296:Mutagenesis; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013455:Sulfur / Q000378:metabolism; D014733:Vibrio / Q000201:enzymology / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D009243:NAD; D005182:Flavin-Adenine Dinucleotide; D013455:Sulfur; D012964:Sodium; D007501:Iron; C084142:sodium-translocating NADH-quinone reductase; D011808:Quinone Reductases