Cytochrome c oxidase subunit III

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

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

Function
is_associated_with::Cytochrome c oxidase is the terminal enzyme of the respiratory chain of is_associated_with::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
 * Cytochrome aa3 quinol oxidase, subunit III