Denitration of peroxynitrite-treated proteins by 'protein nitratases' fromrat brain and heart

Putative 'protein nitratases,' which catalyze denitration of peroxynitrite (PN)-treated proteins, were detected in the homogenate/crude extract of rat brains and hearts. Nitratase activity was monitored by the decreased inten sity of nitrotyrosine immunoreactive-bands in Western blot and increased ni trate level in dialysate of incubation mixture, which contained homogenate/ crude extract, protease inhibitors and a PN-treated substrate, such as trea ted histone (III-S), BSA or invertase. Enhanced activity of nitratases was noted by preincubating crude extract with Ca2+. In addition, at least two t ypes of nitratases may occur: type I, reductant-dependent, and type II, red uctant- independent. Furthermore, upon denitration, the activity of PN-trea ted invertase increased to the same activity level of the untreated inverta se. The overall reaction catalyzed by nitratases for denitration of nitroty rosine residues in protein could be as follows: Protein-Tyr-NO2 + H2O --> P rotein-Tyr-H + H+ + NO3-. The nitration/denitration of protein-tyrosine may be crucial in regulating signal transduction.