The CuAsite of the caa3‐type oxidase of Bacillus subtilis is a mixed‐valence binuclear copper centre

Abstract
A copper-containing domain of the caa3-type oxidase from Bacillus subtilis has been expressed as a water-soluble protein in the cytoplasm of Escherichia coli. Electron paramagnetic resonance (EPR) spectra of this purple domain show well-resolved lines in the gz resonance, both at X-band and S-band frequencies. Interpretation of EPR spectra and analytical data indicate a binuclear copper site consisting of one Cu2+ and one Cu1+. This copper site closely resembles CuA in subunit II of cytochrome c oxidase and is shown here to be a mixed-valence [Cu2+-Cu1+] binuclear centre.