Determination and novel features of the absolute absorption spectra of the heme a moieties in cytochrome c oxidase.

The absolute absorption spectra of the two heme a moieties in cytochrome c oxidase were determined in the Soret region where spectral contributions from copper ions are negligible. This determination employs a set of absorption spectra of the enzyme recorded during anaerobic reduction with sodium dithionite, and does not require any other spectral data. The unique feature of the component spectra revealed in the present study suggests the existence of a specific interaction of heme a with the immediate environment as its origin. The usefulness of the absolute spectra in quantitative analysis of the spectral data is presented.