PROSITE documentation PDOC50253
Heme-copper oxidase subunit III profile


Cytochrome c oxidase (EC 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. This reaction is coupled to the pumping of four additional protons across the mitochondrial or bacterial membrane [1].

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 polypeptidic subunits [2]. The functional role of subunit III is not yet understood.

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 heme-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 [3,4,5].

Last update:

December 2001 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

COX3, PS50253; Heme-copper oxidase subunit III family profile  (MATRIX)


1AuthorsMichel H.
TitleCytochrome c oxidase: catalytic cycle and mechanisms of proton pumping--a discussion.
SourceBiochemistry 38:15129-15140(1999).
PubMed ID10563795

2AuthorsMather M.W. Springer P. Hensel S. Buse G. Fee J.A.
TitleCytochrome oxidase genes from Thermus thermophilus. Nucleotide sequence of the fused gene and analysis of the deduced primary structures for subunits I and III of cytochrome caa3.
SourceJ. Biol. Chem. 268:5395-5408(1993).
PubMed ID8383670

3AuthorsSantana M. Kunst F. Hullo M.F. Rapoport G. Danchin A. Glaser P.
TitleMolecular cloning, sequencing, and physiological characterization of the qox operon from Bacillus subtilis encoding the aa3-600 quinol oxidase.
SourceJ. Biol. Chem. 267:10225-10231(1992).
PubMed ID1316894

4AuthorsChepuri V. Lemieux L. Au D.C. Gennis R.B.
TitleThe sequence of the cyo operon indicates substantial structural similarities between the cytochrome o ubiquinol oxidase of Escherichia coli and the aa3-type family of cytochrome c oxidases.
SourceJ. Biol. Chem. 265:11185-11192(1990).
PubMed ID2162835

5AuthorsGarcia-Horsman J.A. Barquera B. Rumbley J. Ma J. Gennis R.B.
SourceJ. Bacteriol. 176:5587-5600(1994).

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