Electronic states of oxidized and reduced cytochrome c observed by X-ray photoelectron spectroscopy

To understand the mechanism of electrical conductivities of cytochromes in terms of the electronic and valence states, X-ray photoelectron spectra of oxidized and reduced cytochrome c were measured in the Fe 2p, S 2p, O 1s, N 1s and C 1s regions. The difference between the spectra of both forms shows that changes occur in the electronic states at the sites of porphyrin ring and sulfur-containing amino acids (methionine and cysteine residues). The higher conductivity of ferrocytochrome c(reduced form) than ferricytochrome c(oxidized form) is attributed to the charge multiplicity of sulfur atoms in addition to the π-electron system.