Oxidative denitrification of Nω-hydroxy-L-arginine by the superoxide radical anion

The superoxide radical anion (O # −d) produced during the catalytic activity of nitric oxide synthase (NOS) and cytochrome P-450 has been implicated in the oxidative denitrification of hydroxyguanidines ("C ̄NOH). The reactivity of the radiolytically generated O # −d radical with N-hydroxy--arginine (NHA) is pH dependent and appears to parallel the prototropic equilibrium of the hydroxyguanidino group ("C ̄NOHY"C ̄NO−­H+ ; pK ̄ 8). The N-hydroxyguanidino group is more reactive towards O # −d when deprotonated but exhibits negligible reactivity when protonated. Based on a model, the rate constant for the