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  • Title: Stoichiometry and redox behaviour of metals in cytochrome-c oxidase.
    Author: Steffens GC, Soulimane T, Wolff G, Buse G.
    Journal: Eur J Biochem; 1993 May 01; 213(3):1149-57. PubMed ID: 8389295.
    Abstract:
    The early observation of extra copper in preparations of cytochrome-c oxidase has recently lead to a renewed interest in its stoichiometry and possible redox function. In various, pure preparations (heme A contents close to the theoretical value of 9.79 nmol/mg protein for the 13-subunit bovine enzyme) protein-related metal stoichiometries of 3 Cu, 2 Fe, 1 Zn, 1 Mg/monomer with M(r) 204266 were determined. Despite the presence of five potential redox metal ions, reductive and reoxidative titrations indicate the presence of only four one-electron-accepting/donating species in the ligand-free enzyme. Participation of two copper ions in a binuclear copper site acting as one-electron acceptor may explain both the observed copper stoichiometry and the redox behaviour. The homology of the C-terminal sequence of subunit II with one of the copper-binding sites in nitrous-oxide reductases provides possible ligands for complexing two copper ions in a binuclear center.
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