IUBMB Enzyme Nomenclature


Accepted name: quinol—cytochrome-c reductase

Reaction: quinol + 2 ferricytochrome c = quinone + 2 ferrocytochrome c + 2 H+[side 2]

Other name(s): ubiquinol—cytochrome-c reductase; coenzyme Q-cytochrome c reductase; dihydrocoenzyme Q-cytochrome c reductase; reduced ubiquinone-cytochrome c reductase; complex III (mitochondrial electron transport); ubiquinone-cytochrome c reductase; ubiquinol-cytochrome c oxidoreductase; reduced coenzyme Q-cytochrome c reductase; ubiquinone-cytochrome c oxidoreductase; reduced ubiquinone-cytochrome c oxidoreductase; mitochondrial electron transport complex III; ubiquinol-cytochrome c-2 oxidoreductase; ubiquinone-cytochrome b-c1 oxidoreductase; ubiquinol-cytochrome c2 reductase; ubiquinol-cytochrome c1 oxidoreductase; CoQH2-cytochrome c oxidoreductase; ubihydroquinol:cytochrome c oxidoreductase; coenzyme QH2-cytochrome c reductase; QH2:cytochrome c oxidoreductase; ubiquinol:ferricytochrome-c oxidoreductase

Systematic name: quinol:ferricytochrome-c oxidoreductase

Comments: 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: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:


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 (1977) 531-548. [PMID: 597492]

2. Rieske, J.S. Composition, structure, and function of complex III of the respiratory chain. Biochim. Biophys. Acta 456 (1976) 195-247. [PMID: 788795]

3. Wikström, M., Krab, K. and Saraste, M. Proton-translocating cytochrome complexes. Annu. Rev. Biochem. 50 (1981) 623-655. [PMID: 6267990]

4. Sone, N., Tsuchiya, N., Inoue, M. and 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 (1996) 12457-12462. [PMID: 8647852]

5. Yu, J. and 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 (1998) 8860-8866. [PMID: 9535866]

6. Elbehti, A., Nitschke, W., Tron, P., Michel, C. and 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 (1999) 16760-16765. [PMID: 10358017]

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

Return to EC 7.1.1 home page
Return to EC 7.1 home page
Return to EC 7 home page
Return to Enzymes home page
Return to IUBMB Biochemical Nomenclature home page