Multi-frequency epr evidence for a binuclear cua center in cytochrome c oxidase: studies with a 63Cu- and 65 Cu-enriched soluble domain of the cytochrome ba3 subunit II from Thermus Thermophilus James A. Fee, Donita Sanders, Claire E. Slutter, Peter E. Doan, Roland Aasa, Martin Karpefors, and Tore Yanngard. Biochem. Biophys. Res. Comm. 212 77-83 (1995).

SUMMARY We have recorded multi-frequency EPR spectra of 63Cu- and 65Cu- labeled. water-soluble CuA-protein from the cytochrome ba3 of T thermophilus. The spectrum taken at the highest frequency (34.03 GHz shows no hyperfine structure and is nominally axial with apparent g ~ 2 18 and 2.00 The spectrum taken at the lowest frequency (3.93 GHz shows a rich hyperfine structure. Analyses of the spectra show that the observed splitting arises from an interaction of the unpaired electron with two Cu nuclei and support the notion that CUA is a mixed valent [Cu(II)/Cu(I)] complex in which the unpaired electronic spin is distributed evenly over the two Cu ions.