Cytochrome c oxidase

The enzyme cytochrome c oxidase (PDB 2OCC (http://www.rcsb.org/pdb/cgi/explore.cgi?pid=85881034355622&page=0&pdbId=2OCC), EC 1.9.3.1 ) is a large transmembrane protein found in the mitochondrion and is the terminal electron acceptor in the electron transfer chain, taking 4 reducing equivalents from cytochrome c and converting molecular oxygen to water. In the process, it translocates protons, helping to establish a chemiosmotic potential that the ATP synthase then uses to synthesize ATP.

Summary reaction:

4 Fe⁺²-cytochrome c + 4H⁺ + O₂ → 4 Fe⁺³-cytochrome c + H₂O.

The complex is a large lipoprotein composed of several metal prosthetic sites and 13 protein subunits. In mammals, 10 subunits are nuclear in origin and 3 are synthesized mitochondrially. The complex contains 2 cytochromes, the a and a₃ cytochromes, and two copper centers, the Cu_A and Cu_B centers. In fact, the cytochrome a₃ and Cu_B are a binuclear center that is the site of oxygen reduction. The mechanism of action of this large complex is still an active research topic.

Further information

The Cytochrome Oxidase home page (http://www-bioc.rice.edu/~graham/CcO.html)