<prompt> Cytochromes arePyridine nucelotidesMetal containing flavoproteinsPeroxidasesIron-porphyrin proteins  <response>: Cytochromes These are very impoant enzymes which contain haem and are involved in cellular oxidation. Fe-porphyrin protein The oxidized form of cytochrome possesses a single Fe3 ion and is called ferricytochrome. It is reduced to ferrocytochrome having a Fe2 ion on accepting an electron. Cytochromes are identified by their characteristic absorption spectra. Ferricytochrome shows diffuse and non-characteristic absorption band invisible spectrum. Ferrocytochrome exhibit characteristic absorption bands called a aa, b bb, and ggg-soret bands. Cytochromes are categorized into different groups according to the light wavelength at which the a-band shows its peak a absorption maxima. They also differ with respect to haem prosthetic group, the apoprotein, and binding between the haem and apoprotein.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th edition, page no: 137 