Detection of Peroxynitrite in Biological Fluids

Peroxynitrite (ONOO⁻ ) is both an oxidant and a nitrating agent (1 –3 ). However, unlike other strong oxidants, peroxynitrite reacts selectively with biological targets. This selectivity is derived in part from the different second-order rate constants (vary from 10³ –10⁶ M ⁻¹ s⁻¹ ) by which ONOO⁻ reacts with biological targets. Competing for peroxynitrite-mediated oxidation of biological targets are two pathways. One is the protonation to form peroxynitrous acid and the second is the reaction with CO₂ . Peroxynitrous acid is also an oxidant but it readily isomerizes to nitrate. The reaction with CO₂ results in the formation of the ONO(O)CO₂ ⁻ adduct that is a more potent nitrating agent but a weaker oxidant than peroxynitrite. Peroxynitrite can diffuse through biological membranes before it encounters and reacts with biological targets. This observation implies that diffusion can effectively compete with the isomerization to nitrate or the reaction with CO₂ .