title: Possible roles of two quinone molecules in direct and indirect proton pumps of bovine heart NADH-quinone oxidoreductase (complex I).
abstract: In many energy transducing systems which couple electron and proton transport, for example, bacterial photosynthetic reaction center, cytochrome bc(1)-complex (complex III) and E. coli quinol oxidase (cytochrome bo(3) complex), two protein-associated quinone molecules are known to work together. T. Ohnishi and her collaborators reported that two distinct semiquinone species also play important roles in NADH-ubiquinone oxidoreductase (complex I). They were called SQ(Nf) (fast relaxing semiquinone) and SQ(Ns) (slow relaxing semiquinone). It was proposed that Q(Nf) serves as a "direct" proton carrier in the semiquinone-gated proton pump (Ohnishi and Salerno, FEBS Letters 579 (2005) 4555), while Q(Ns) works as a converter between one-electron and two-electron transport processes. This communication presents a revised hypothesis in which Q(Nf) plays a role in a "direct" redox-driven proton pump, while Q(Ns) triggers an "indirect" conformation-driven proton pump. Q(Nf) and Q(Ns) together serve as (1e(-)/2e(-)) converter, for the transfer of reducing equivalent to the Q-pool.
authors.affiliation: Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
authors.forename: S Tsuyoshi
authors.initials: ST
authors.lastname: Ohnishi
authors.forename: John C
authors.initials: JC
authors.lastname: Salerno
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism*; D001692:Biological Transport; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D004579:Electron Transport; D042967:Electron Transport Complex I / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D017494:Proton Pumps / Q000737:chemistry / Q000378:metabolism*; D011522:Protons
chemical_list: D016227:Benzoquinones; D017494:Proton Pumps; D011522:Protons; D009243:NAD; C004532:quinone; D042967:Electron Transport Complex I