The nature of CuA in cytochrome c oxidase

Abstract

Kroneek 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 Cu_A. 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 Cu_A site.