The free radical-mediated damage to proteins results in the modification of amino acid residues, cross-linking of side chains and fragmentation. L-tyrosine and protein bound tyrosine are prone to attack by various mediators and reactive nitrogen intermediates to form 3-nitrotyrosine (3-NT). 3-NT formation is also catalyzed by a class of peroxidases utilizing nitrite and hydrogen peroxide as substrates. Evidence supports the formation of 3-NT in vivo in diverse pathologic conditions and 3-NT is thought to be a relatively specific marker of oxidative damage. The formation of nitrotyrosine represents a specific peroxynitrite-mediated protein modification; thus, detection of nitrotyrosine in proteins is considered as a biomarker for endogenous peroxynitrite activity. Formation of tyrosine nitrated proteins is considered to be a post-translational modification with important pathophysiological consequences and is one of the markers of nitrosative stress that have been reported in neurodegeneration, inflammatory and other pathological conditions....