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Cytochrome c oxidase is a three-copper, two-heme-A protein.

Metal contents of preparations of procaryotic (Paracoccus denitrificans) and eucaryotic (beef heart) cytochrome c oxidases have been determined by inductively coupled plasma atomic emission spectroscopy and shown to be stoichiometrically related to the protein contents. The results show that oxidases which possess subunits I and II have three copper atoms besides hemes a and a3 (Paracoccus denitrificans, Cu: 2.97 +/- 0.08 and Fe: 2.09 +/- 0.10; bovine heart, Cu: 2.83 +/- 0.07 and Fe: 1.94 +/- 0.12). Together with data reported for the c1 aa3 oxidase from Thermus thermophilus, the following conclusions can be drawn. Subunit I binds two copper atoms and both hemes a and a3 and thus is the universal terminal oxidase of this spectral type. Subunit II binds one copper and functions as an electron conductor. The mitochondrial respiratory complex IV binds, in addition to three copper and two hemes a, stoichiometric amounts of magnesium and zinc (bovine heart Mg: 0.98 +/- 0.05 and Zn: 1.01 +/- 0.04).