Cytochrome c is an essential component of the respiratory electron transport chain in mitochondria. The heme group of cytochrome c accepts electrons from the bc Complex III and transports them to Complex IV, while it transfers energy in the opposite direction.
Cytochrome c can also catalyze several redox reactions such as hydroxylation and aromatic oxidation, and shows peroxidase activity by oxidation of various electron donors such as 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2-keto-4-thiomethyl butyric acid and 4-aminoantipyrine.
A bacterial cytochrome c functions as a nitrite reductase.