Cytochrome c oxidase subunit I

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Cytochrome c oxidase subunit I
PBB Protein COX1 image.jpg
PDB rendering based on 1occ.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols COX1 ; COI; MTCO1
External IDs OMIM516030 MGI102504 HomoloGene5016 ChEMBL: 6173 GeneCards: COX1 Gene
Species Human Mouse
Entrez 4512 17708
Ensembl ENSG00000198804 ENSMUSG00000064351
UniProt P00395 n/a
RefSeq (mRNA) n/a n/a
RefSeq (protein) n/a NP_904330
Location (UCSC) Chr MT:
0.01 – 0.01 Mb
Chr MT:
0.01 – 0.01 Mb
PubMed search [1] [2]
Cytochrome c oxidase subunit I
PDB 1occ EBI.jpg
Structure of the 13-subunit oxidized cytochrome c oxidase.[1]
Symbol COX1 or COI
Pfam PF00115
InterPro IPR000883
SCOP 1occ
TCDB 3.D.4
OPM superfamily 4
OPM protein 1v55
CDD cd01663
"Cox1" redirects here. Particularly in a medical context, this can also refer to cyclooxygenase-1 (COX-1).

Cytochrome c oxidase I (COX1) also known as mitochondrially encoded cytochrome c oxidase I (MT-CO1) is a protein that in humans is encoded by the MT-CO1 gene.[2] In other eukaryotes, the gene is called COX1, CO1, or COI.[3] Cytochrome c oxidase I is the main subunit of the cytochrome c oxidase complex.


Cytochrome c oxidase subunit I (CO1 or MT-CO1) is one of three mitochondrial DNA (mtDNA) encoded subunits (MT-CO1, MT-CO2, MT-CO3) of respiratory complex IV. Complex IV is the third and final enzyme of the electron transport chain of mitochondrial oxidative phosphorylation.[2]

Cytochrome c oxidase (EC is a key enzyme in aerobic metabolism. Proton pumping heme-copper oxidases represent the terminal, energy-transfer enzymes of respiratory chains in prokaryotes and eukaryotes. The CuB-heme a3 (or heme o) binuclear centre, associated with the largest subunit I of cytochrome c and ubiquinol oxidases (EC, is directly involved in the coupling between dioxygen reduction and proton pumping.[4][5] Some terminal oxidases generate a transmembrane proton gradient across the plasma membrane (prokaryotes) or the mitochondrial inner membrane (eukaryotes).

The enzyme complex consists of 3-4 subunits (prokaryotes) up to 13 polypeptides (mammals) of which only the catalytic subunit (equivalent to mammalian subunit I (COI)) is found in all heme-copper respiratory oxidases. The presence of a bimetallic centre (formed by a high-spin heme and copper B) as well as a low-spin heme, both ligated to six conserved histidine residues near the outer side of four transmembrane spans within COI is common to all family members.[6][7][8] In contrast to eukaryotes the respiratory chain of prokaryotes is branched to multiple terminal oxidases. The enzyme complexes vary in heme and copper composition, substrate type and substrate affinity. The different respiratory oxidases allow the cells to customize their respiratory systems according to a variety of environmental growth conditions.[4]

It has been shown that eubacterial quinol oxidase was derived from cytochrome c oxidase in Gram-positive bacteria and that archaebacterial quinol oxidase has an independent origin. A considerable amount of evidence suggests that proteobacteria (Purple bacteria) acquired quinol oxidase through a lateral gene transfer from Gram-positive bacteria.[4]

A related nitric-oxide reductase (EC exists in denitrifying species of archaea and eubacteria and is a heterodimer of cytochromes b and c. Phenazine methosulphate can act as acceptor. It has been suggested that cytochrome c oxidase catalytic subunits evolved from ancient nitric oxide reductases that could reduce both nitrogen and oxygen.[9][10]



It is a gene that is often used as a DNA barcode to identify animal species. MT-CO1 gene sequence is suitable for this role because its mutation rate is often fast enough to distinguish closely related species and also because its sequence is conserved among conspecifics. Contrary to the primary objection raised by skeptics that MT-CO1 sequence differences are too small to be detected between closely related species, more than 2% sequence divergence is typically detected between such organisms,[11] suggesting that the barcode is effective. In most if not all seed plants, however, the rate of evolution of cox1 is very slow.


  1. ^ Tsukihara T, Aoyama H, Yamashita E et al. (May 1996). "The whole structure of the 13-subunit oxidized cytochrome c oxidase at 2.8 A". Science 272 (5265): 1136–44. Bibcode:1996Sci...272.1136T. doi:10.1126/science.272.5265.1136. PMID 8638158. 
  2. ^ a b "Entrez Gene: Cytochrome c oxidase subunit I". 
  3. ^ Kosakyan A, Heger TJ, Leander BS, Todorov M, Mitchell EA, Lara E (May 2012). "COI barcoding of Nebelid testate amoebae (Amoebozoa: Arcellinida): extensive cryptic diversity and redefinition of the Hyalospheniidae Schultze". Protist 163 (3): 415–34. doi:10.1016/j.protis.2011.10.003. PMID 22130576. 
  4. ^ a b c 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 196760. PMID 8083153. 
  5. ^ Glaser P, Villani G, Papa S, Capitanio N (1994). "The proton pump of heme-copper oxidases". Cell Biol. Int. 18 (5): 345–355. doi:10.1006/cbir.1994.1084. PMID 8049679. 
  6. ^ Saraste M, Castresana J, Higgins DG, Lubben M (1994). "Evolution of cytochrome oxidase, an enzyme older than atmospheric oxygen". EMBO J. 13 (11): 2516–2525. PMC 395125. PMID 8013452. 
  7. ^ Capaldi RA, Malatesta F, Darley-Usmar VM (1983). "Structure of cytochrome c oxidase". Biochim. Biophys. Acta 726 (2): 135–48. doi:10.1016/0304-4173(83)90003-4. PMID 6307356. 
  8. ^ Saraste M, Holm L, Wikstrom M (1987). "Structural models of the redox centres in cytochrome oxidase". EMBO J. 6 (9): 2819–2823. PMC 553708. PMID 2824194. 
  9. ^ Saraste M, Castresana J (March 1994). "Cytochrome oxidase evolved by tinkering with denitrification enzymes". FEBS Lett. 341 (1): 1–4. doi:10.1016/0014-5793(94)80228-9. PMID 8137905. 
  10. ^ Chen J, Strous M (February 2013). "Denitrification and aerobic respiration, hybrid electron transport chains and co-evolution". Biochim. Biophys. Acta 1827 (2): 136–44. doi:10.1016/j.bbabio.2012.10.002. PMID 23044391. 
  11. ^ Hebert PD, Ratnasingham S, deWaard JR (August 2003). "Barcoding animal life: cytochrome c oxidase subunit 1 divergences among closely related species". Proc. Biol. Sci. 270 Suppl 1: S96–9. doi:10.1098/rsbl.2003.0025. PMC 1698023. PMID 12952648. 

Further reading[edit]


This article incorporates text from the public domain Pfam and InterPro IPR000883