Cytochrome c oxidase
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CytochromeCOxidase-2OCC.png
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 (http://www.expasy.org/cgi-bin/nicezyme.pl?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 CuA and CuB centers. In fact, the cytochrome a3 and CuB 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.
Cyanide, carbon monoxide and azide all bind irreversibly to Cytochrome c Oxidase. The protein is then inhibited from functioning, causing chemical suffocation.
External link
- The Cytochrome Oxidase home page (http://www-bioc.rice.edu/~graham/CcO.html)