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

Biochim Biophys Acta. 2010 Dec;1797(12):1891-3. doi: 10.1016/j.bbabio.2010.06.010. Epub 2010 Jun 25.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Benzoquinones / chemistry
  • Benzoquinones / metabolism*
  • Biological Transport
  • Cattle
  • Cell Membrane / metabolism
  • Electron Transport
  • Electron Transport Complex I / chemistry
  • Electron Transport Complex I / metabolism*
  • Hydrogen-Ion Concentration
  • Models, Biological
  • Myocardium / enzymology*
  • NAD / metabolism
  • Oxidation-Reduction
  • Proton Pumps / chemistry
  • Proton Pumps / metabolism*
  • Protons


  • Benzoquinones
  • Proton Pumps
  • Protons
  • NAD
  • quinone
  • Electron Transport Complex I