Formation of nitrotyrosine by methylene blue photosensitized oxidation of tyrosine in the presence of nitrite

Methylene blue photosensitized oxidation of tyrosine in the presence of nit rite produces 3-nitrotyrosine, with maximum yield at pH 6. The formation of 3-nitrotyrosine requires oxygen and increases using deuterium oxide as sol vent, suggesting the involvement of singlet oxygen in the reaction. The det ection of dityrosine as an additional reaction product suggests that the fi rst step in the interaction of tyrosine with singlet oxygen generates tyros yl radicals which can dimerize to form dityrosine or react with a nitrite-d erived species to produce 3-nitrotyrosine. Although the chemical identity o f the nitrating species has not been established, the possible generation o f nitrogen dioxide (NO2) by indirect oxidation of nitrite by intermediately produced tyrosyl radical, via electron transfer, is proposed. One importan t implication of the results of this study is that the oxidation of tyrosin e by singlet oxygen in the presence of nitrite may represent an alternative or additional pathway of 3-nitrotyrosine formation of potential importance in oxidative injures such as during inflammatory processes. (C) 2001 Acade mic Press.