Resonance Raman spectroscopy (excitation at 647.1 nm) of solubilized and aerated cytochrome oxidase d from Escherichia coli K12 has shown absorptions (1078–1105 cm−1) attributed to the oxygen—oxygen stretching frequency of the oxidase—oxygen adduct. These findings support the hypothesis that the 650–652 nm chromophore of cytochrome d is an oxygenated or ’oxy’ intermediate species and not the fully oxidized enzyme.
