The protonmotive Q cycle. Energy transduction by coupling of proton translocation to electron transfer by the cytochrome bc1 complex.

The cytochrome bcl complex is an oligomeric membrane protein complex which is a component of the mitochondrial respiratory chain and of the electron transfer chains of numerous bacteria which use oxygen, nitrogen, and sulfur compounds as terminal electron acceptors

B L Trumpower

2021

Scholarcy highlights

  • The cytochrome bcl complex is an oligomeric membrane protein complex which is a component of the mitochondrial respiratory chain and of the electron transfer chains of numerous bacteria which use oxygen, nitrogen, and sulfur compounds as terminal electron acceptors
  • In bacteria the bq complex is located in the plasma membrane, and the periplasmic side of the membrane is positive relative to the cytoplasm
  • The protonmotive Q cycle accounts for the stoichiometry of proton translocation in the bcl complex and, as explained below, uniquely accounts for how cytochrome b-566, which has an oxidation-reduction potential much more negative than that of the ubiquinone/ubiquinol couple, can participate in oxidation of ubiquinol
  • If’the protonmotive Q cycle is correct, one would expect that the iron-sulfur protein is required for oxidant-induced b reduction, and center P inhibitors would block this reaction
  • The divergent oxidation of ubiquinol at center P requires that the ubiquinol oxidase site is close to both the iron-sulfur cluster and the b-566 heme since there must be a significant kinetic advantage to electron transfer from QT to b-566 to overcome the 350 mV increment in potentials which otherwise favors reduction of the iron-sulfur cluster by the strongly reducing Qr. Center P must exclude water and oxygen; otherwise Qg would react promiscuously

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