Integral complexes of cytochrome c oxidase contain three coppers

Metal contents have been determined in beef heart cytochrome c oxidase by inductively coupled plasma atomic emission spectroscopy. Integral complexes of this enzyme contain three copper and two iron atoms, as well as one zinc and one magnesium atom (Cu: 2, 91 +/- 0, 13; Fe: 2, 05 +/- 0, 17; Zn: 1, 03 +/- 0, 03; Mg: 1, 01 +/- 0, 10). The combination of these results with those reported for the c1 aa3-oxidase from Thermus thermophilus leads to the conclusion that subunit I is the universal two coppers and two hemes a binding catalytic unit common to all oxidases of the aa3-type. Subunit II, which binds the third copper ion, functions as an electron conducting unit, transferring electrons from cytochrome c to the four redox centers in subunit I. Preliminary titration experiments with NADH reveal, in agreement with this catalytic organisation, the presence of five redox centers.