{PDOC50253}
{PS50253; COX3}
{BEGIN}
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* Heme-copper oxidase subunit III profile *
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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. 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].

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2001 / First entry.

[ 1] Michel H.
     "Cytochrome c oxidase: catalytic cycle and mechanisms of proton
     pumping--a discussion."
     Biochemistry 38:15129-15140(1999).
     PubMed=10563795; DOI=10.1021/bi9910934
[ 2] Mather M.W., Springer P., Hensel S., Buse G., Fee J.A.
     "Cytochrome 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."
     J. Biol. Chem. 268:5395-5408(1993).
     PubMed=8383670
[ 3] Santana M., Kunst F., Hullo M.F., Rapoport G., Danchin A., Glaser P.
     "Molecular cloning, sequencing, and physiological characterization of
     the qox operon from Bacillus subtilis encoding the aa3-600 quinol
     oxidase."
     J. Biol. Chem. 267:10225-10231(1992).
     PubMed=1316894
[ 4] Chepuri V., Lemieux L., Au D.C., Gennis R.B.
     "The 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."
     J. Biol. Chem. 265:11185-11192(1990).
     PubMed=2162835
[ 5] Garcia-Horsman J.A., Barquera B., Rumbley J., Ma J., Gennis R.B.
     J. Bacteriol. 176:5587-5600(1994).

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