Cytochrome c oxidase subunit III

"COX3" redirects here. For the cyclooxygenase isoenzyme, see COX-3.

Cytochrome c oxidase subunit III
File:PDB 1occ EBI.jpg Structure of the 13-subunit oxidized cytochrome c oxidase.
Identifiers
Symbol	COX3
Pfam	PF00510
InterPro	IPR000298
PROSITE	PDOC50253
SCOP	1occ
SUPERFAMILY	1occ
TCDB	3.D.4
OPM superfamily	4
OPM protein	1v55
CDD	cd01665
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

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

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

Function

Cytochrome c oxidase (EC 1.9.3.1) 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 $\rightleftharpoons$ 4 cytochrome c⁺³ + 2 H₂O

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

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.

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.

Clinical significance

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

Subfamilies

• Cytochrome o ubiquinol oxidase, subunit III IPR014206
• Cytochrome aa3 quinol oxidase, subunit III IPR014246

External links

• GeneReviews/NCBI/NIH/UW entry on Mitochondrial DNA-Associated Leigh Syndrome and NARP