UV photolysis of 3-nitrotyrosine generates highly oxidizing species: a potential source of photooxidative stress.

Laser flash photolysis at 266 nm of 3-nitrotyrosine and N-acetyl-3-nitrotyrosine ethyl ester generates an oxidizing species, which shows all of the characteristics of a hydroxyl radical. This species reacts with Br(-) to yield Br(2).-, via an intermediate, that is kinetically identified as HOBr.-. Moreover, the formation of Br(2).- can be suppressed by methanol; competition kinetics yield relative rate constants for the reaction of the reactive species with Br(-) and methanol that are similar to those for the hydroxyl radical. Parallel time-resolved UV/vis spectroscopy suggests the formation of phenoxyl radicals, consistent with the formation of hydroxyl radicals. Laser flash photolysis at 355 nm also generates reactive intermediates that oxidize Br(-) to Br(2).- but appear not to be hydroxyl radicals.