Possible roles of two quinone molecules in direct and indirect proton pumps of bovine heart NADH-quinone oxidoreductase (complex I)

• Published in: Biochimica et biophysica acta Vol. 1797; no. 12; pp. 1891 - 1893
• Main Authors: Ohnishi, S. Tsuyoshi, Salerno, John C., Ohnishi, Tomoko
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2010
• Subjects: Animals; Benzoquinones - chemistry; Benzoquinones - metabolism; Biological Transport; Cattle; Cell Membrane - metabolism; Direct proton pump; Electron Transport; Electron Transport Complex I - chemistry; Electron Transport Complex I - metabolism; Hydrogen-Ion Concentration; Indirect proton pump; Models, Biological; Myocardium - enzymology; NAD - metabolism; Oxidation-Reduction; Proton Pumps - chemistry; Proton Pumps - metabolism; Protons; Quinone-gated proton pump; Quinone-induced conformation-driven proton pump; Quinone-gated proton pump; SQ Ns; DBQ; Quinone-induced conformation-driven proton pump; Complex I; Direct proton pump; Indirect proton pump; SQ Nf
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2010.06.010

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.