Regulation of cytochrome C peroxidase activity by nitric oxide and laser irradiation.

Apoptosis can be induced by activation of so-called "death receptors" (extrinsic pathway) or multiple apoptotic factors (intrinsic pathway), which leads to release of cytochrome c from mitochondria. This event is considered to be a point of no return in apoptosis. One of the most important events in the development of apoptosis is the enhancement of cytochrome c peroxidase activity upon its interaction with cardiolipin, which modifies the active center of cytochrome c. In the present work, we have investigated the effects of nitric oxide on the cytochrome c peroxidase activity when cytochrome c is bound to cardiolipin or sodium dodecyl sulfate. We have observed that cytochrome c peroxidase activity, distinctly increased due to the presence of anionic lipids, is completely suppressed by nitric oxide. At the same time, nitrosyl complexes of cytochrome c, produced in the interaction with nitric oxide, demonstrated sensitivity to laser irradiation (441 nm) and were photolyzed during irradiation. This decomposition led to partial restoration of cytochrome c peroxidase activity. Finally, we conclude that nitric oxide and laser irradiation may serve as effective instruments for regulating the peroxidase activity of cytochrome c, and, probably, apoptosis.