Nitration of specific tyrosine residues of cytochrome C is associated with caspase-cascade inactivation.

Peroxynitrite, a potent oxidative stress inducer, inhibits the mitochondrial electron transfer, induces cell death, and is considered to be involved in the pathology of various diseases. However, the intracellular mechanisms involved in the cell death process are not fully understood. Here we demonstrate that the enhanced nitration of specific tyrosine residues of cytochrome c, which are induced by continuous peroxynitrite exposure, attenuates cytochrome c-induced caspase-9 activation in vitro. Interestingly, cytochrome c nitrated with a single high dose of peroxynitrite preserved its potency, while this did not occur when cytochrome c was treated with continuous peroxynitrite exposure. Although both of these experiments resulted in cytochrome c nitration at the tyrosine residues, it was found that nitration at specific residues was enhanced only when cytochrome c was exposed to continuous peroxynitrite. This is the first report to demonstrate that cytochrome c nitration affects the apoptotic pathway by means of enhancement of nitration at specific tyrosine residues. This result implies that the nitration pattern of cytochrome c may affect the efficacy of the mitochondrial pathway in apoptotic cell death.