cytochrome

Any of a group of cell proteins (hemoproteins) that serve a vital function in the transfer of energy within cells. Hemoproteins are linked to a nonprotein, iron-bearing component (a heme group), which can undergo the reversible oxidation-reduction reactions that yield energy for the cell. Cytochromes are subdivided into three classes depending on what wavelengths of light they absorb. At least 30 different cytochromes have been identified.