Cytochrome c oxidase subunit III

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"COX3" redirects here. For the cyclooxygenase isoenzyme, see COX-3.
Aliases COX3, COIII, MTCO3, Cytochrome c oxidase subunit III, cytochrome c oxidase III
External IDs HomoloGene: 5014 GeneCards: 4514
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr M: 0.01 – 0.01 Mb n/a
PubMed search [1] n/a
View/Edit Human
Location of the MT-CO3 gene in the human mitochondrial genome. MT-CO3 is one of the three cytochrome c oxidase subunit mitochondrial genes (orange boxes).
Cytochrome c oxidase subunit III
PDB 1occ EBI.jpg
Structure of the 13-subunit oxidized cytochrome c oxidase.[2]
Symbol COX3
Pfam PF00510
InterPro IPR000298
SCOP 1occ
TCDB 3.D.4
OPM superfamily 4
OPM protein 1v55
CDD cd01665

Cytochrome c oxidase subunit 3 is an enzyme that in humans is encoded by the MT-CO3 gene.[3]

Cytochrome c oxidase subunit III is one of main transmembrane subunits of cytochrome c oxidase.


Cytochrome c oxidase (EC is the terminal enzyme of the respiratory chain of mitochondria and many aerobic bacteria. It catalyzes the transfer of electrons from reduced cytochrome c to molecular oxygen:

4 cytochrome c+2 + 4 H+ + O2 4 cytochrome c+3 + 2 H2O

This reaction is coupled to the pumping of four additional protons across the mitochondrial or bacterial membrane.[4][5]

Cytochrome c oxidase is an oligomeric enzymatic complex that is located in the mitochondrial inner membrane of eukaryotes and in the plasma membrane of aerobic prokaryotes. The core structure of prokaryotic and eukaryotic cytochrome c oxidase contains three common subunits, I, II and III. In prokaryotes, subunits I and III can be fused and a fourth subunit is sometimes found, whereas in eukaryotes there are a variable number of additional small subunits.[6]

As the bacterial respiratory systems are branched, they have a number of distinct terminal oxidases, rather than the single cytochrome c oxidase present in the eukaryotic mitochondrial systems. Although the cytochrome o oxidases do not catalyze the cytochrome c but the quinol (ubiquinol) oxidation they belong to the same haem-copper oxidase superfamily as cytochrome c oxidases. Members of this family share sequence similarities in all three core subunits: subunit I is the most conserved subunit, whereas subunit II is the least conserved.[7][8][9]

Clinical significance[edit]

Mutations in mtDNA-encoded cytochrome c oxidase subunit genes have been observed to be associated with isolated myopathy or severe encephalomyopathy.[10]



  1. ^ "Human PubMed Reference:". 
  2. ^ Miki K, Sogabe S, Uno A, et al. (May 1994). "Application of an automatic molecular-replacement procedure to crystal structure analysis of cytochrome c2 from Rhodopseudomonas viridis". Acta Crystallogr. D. 50 (Pt 3): 271–5. doi:10.1107/S0907444993013952. PMID 15299438. 
  3. ^ "Entrez Gene: COX3 cytochrome c oxidase subunit III". 
  4. ^ Michel H (1999). "Cytochrome c oxidase: catalytic cycle and mechanisms of proton pumping--a discussion". Biochemistry. 38 (46): 15129–15140. doi:10.1021/bi9910934. PMID 10563795. 
  5. ^ Wikstrom M, Belevich I, Verkhovsky MI (2006). "Proton-coupled electron transfer drives the proton pump of cytochrome c oxidase". Nature. 440 (7085): 829–32. doi:10.1038/nature04619. PMID 16598262. 
  6. ^ Mather MW, Springer P, Hensel S, Buse G, Fee JA (1993). "Cytochrome oxidase genes from Thermus thermophilus. Nucleotide sequence of the fused gene and analysis of the deduced primary structures for subunits I and III of cytochrome caa3". J. Biol. Chem. 268 (8): 5395–5408. PMID 8383670. 
  7. ^ Danchin A, Glaser P, Kunst F, Rapoport G, Santana M, Hullo MF (1992). "Molecular cloning, sequencing, and physiological characterization of the qox operon from Bacillus subtilis encoding the aa3-600 quinol oxidase". J. Biol. Chem. 267 (15): 10225–10231. PMID 1316894. 
  8. ^ Lemieux L, Gennis RB, Chepuri V, Au DC (1990). "The sequence of the cyo operon indicates substantial structural similarities between the cytochrome o ubiquinol oxidase of Escherichia coli and the aa3-type family of cytochrome c oxidases". J. Biol. Chem. 265 (19): 11185–11192. PMID 2162835. 
  9. ^ Rumbley J, Gennis RB, Garcia-Horsman JA, Barquera B, Ma J (1994). "The superfamily of heme-copper respiratory oxidases". J. Bacteriol. 176 (18): 5587–5600. PMC 196760free to read. PMID 8083153. 
  10. ^ Horváth, R; Schoser, BG; Müller-Höcker, J; Völpel, M; Jaksch, M; Lochmüller, H (2005). "Mutations in mtDNA-encoded cytochrome c oxidase subunit genes causing isolated myopathy or severe encephalomyopathy". Neuromuscular disorders : NMD. 15 (12): 851–7. doi:10.1016/j.nmd.2005.09.005. PMID 16288875. 

Further reading[edit]

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