Cytochrome c, an ideal antioxidant

Generation of DeltaPsi (membrane potential) by cytochrome oxidase proteoliposomes oxidizing superoxide-reduced cytochrome c has been demonstrated. XO+HX (xanthine oxidase and hypoxanthine) were used to produce superoxide. It was found that the generation of DeltaPsi is completely abolished by cyanide (an uncoupler) or by superoxide dismutase, and is enhanced by nigericin. Addition of ascorbate after XO+HX causes a further increase in DeltaPsi. On the other hand, XO+HX added after ascorbate do not affect DeltaPsi, indicating that superoxide does not have measurable protonophorous activity. The half-maximal cytochrome c concentration for DeltaPsi generation supported by XO+HX was found to be approx. 1 microM. These data and the results of some other researchers can be rationalized as follows: (1) O(2) accepts an electron to form superoxide; (2) cytochrome c oxidizes superoxide back to O(2); (3) an electron removed from the reduced cytochrome c is transferred to O(2) by cytochrome oxidase in a manner that generates Deltamicro(H(+)) (transmembrane difference in electrochemical H(+) potential). Thus cytochrome c mediates a process of superoxide removal, resulting in regeneration of O(2) and utilization of the electron involved previously in the O(2) reduction. It is important that cytochrome c is not damaged during the antioxidant reaction, in contrast with many other antioxidants.