The redox properties of the cytochromes of purified Complex III

Purified Complex III from beef heart contains two b cytochromes: a high-potential (E_{m 7.2} = +93 mV) cytochrome b-562 which can be enzymatically reduced, and a low-potential (E_{m 7.2} = −34 mV) cytochrome b-565 which is reduced only by dithionite. The two components each contribute approximately 50% to the total cytochrome b of Complex III. Cytochrome c₁ of Complex III titrates with a half-reduction potential of +232 mV.