EC - Quinol—cytochrome-c reductase

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IntEnz Enzyme Nomenclature


Accepted name:
quinol—cytochrome-c reductase
Other names:
CoQH2—cytochrome c oxidoreductase
QH2:cytochrome c oxidoreductase
coenzyme Q—cytochrome c reductase
coenzyme QH2—cytochrome c reductase
dihydrocoenzyme Q—cytochrome c reductase
mitochondrial electron transport complex III
reduced coenzyme Q-cytochrome c reductase
reduced ubiquinone—cytochrome c oxidoreductase
reduced ubiquinone—cytochrome c reductase, complex III (mitochondrial electron transport)
ubihydroquinol:cytochrome c oxidoreductase
ubiquinol—cytochrome c oxidoreductase
ubiquinol—cytochrome c-2 oxidoreductase
ubiquinol—cytochrome c1 oxidoreductase
ubiquinol—cytochrome c2 reductase
ubiquinone-cytochrome c reductase
ubiquinone—cytochrome b-c1 oxidoreductase
ubiquinone—cytochrome c oxidoreductase
ubiquinone—cytochrome-c oxidoreductase
cytochrome bc1 complex
complex III (mitochondrial electron transport)
ubiquinol:ferricytochrome-c oxidoreductase
ubiquinol—cytochrome-c reductase
Systematic name:
quinol:ferricytochrome-c oxidoreductase



The enzyme, often referred to as the cytochrome bc1 complex or complex III, is the third complex in the electron transport chain. It is present in the mitochondria of all aerobic eukaryotes and in the inner membranes of most bacteria. The mammalian enzyme contains cytochromes b-562, b-566 and c1, and a 2-iron ferredoxin. Depending on the organism and physiological conditions, the enzyme extrudes either two or four protons from the cytoplasmic to the non-cytoplasmic compartment (cf. EC, NADH dehydrogenase).

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00171
Structural data: CSA , EC2PDB
UniProtKB/Swiss-Prot: (58) [show] [UniProt]


  1. Marres, C.A.M. and Slater, E.C.
    Polypeptide composition of purified QH2:cytochrome c oxidoreductase from beef-heart mitochondria.
    Biochim. Biophys. Acta 462: 531-548 (1977). [PMID: 597492]
  2. Rieske, J.S.
    Composition, structure, and function of complex III of the respiratory chain.
    Biochim. Biophys. Acta 456: 195-247 (1976). [PMID: 788795]
  3. Wikström, M., Krab, K. and Saraste, M.
    Proton-translocating cytochrome complexes.
    Annu. Rev. Biochem. 50: 623-655 (1981). [PMID: 6267990]
  4. Sone, N., Tsuchiya, N., Inoue, M., Noguchi, S.
    Bacillus stearothermophilus qcr operon encoding rieske FeS protein, cytochrome b6, and a novel-type cytochrome c1 of quinol-cytochrome c reductase.
    J. Biol. Chem. 271: 12457-12462 (1996). [PMID: 8647852]
  5. Yu, J., Le Brun, N. E.
    Studies of the cytochrome subunits of menaquinone:cytochrome c reductase (bc complex) of Bacillus subtilis. Evidence for the covalent attachment of heme to the cytochrome b subunit.
    J. Biol. Chem. 273: 8860-8866 (1998). [PMID: 9535866]
  6. Elbehti, A., Nitschke, W., Tron, P., Michel, C., Lemesle-Meunier, D.
    Redox components of cytochrome bc-type enzymes in acidophilic prokaryotes. I. Characterization of the cytochrome bc1-type complex of the acidophilic ferrous ion-oxidizing bacterium Thiobacillus ferrooxidans.
    J. Biol. Chem. 274: 16760-16765 (1999). [PMID: 10358017]

[EC created 1978 as EC, modified 2013, transferred 2018 to EC]