The nature of CuA in cytochrome c oxidase.

Kroneck et al. [(1988) FEBS Lett. 242, 70-74] have recently suggested, on the basis of a comparison with the EPR properties of nitrous oxide reductase, that cytochrome c oxidase contains a mixed-valence binuclear copper site, and that this is responsible for the EPR spectrum generally ascribed to CuA. Here we question this hypothesis in view of a multitude of analytical and spectroscopic data available. We maintain that a mononuclear Cu site with two cysteine sulfur and two imidazole nitrogen atoms as ligands is consistent with the current experimental information on the CuA site.