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

Abstract

The superoxide radical anion (O2-.) 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 O2-. radical with N omega-hydroxy-L-arginine (NHA) is pH dependent and appears to parallel the prototropic equilibrium of the hydroxyguanidino group ( > C = NOH reversible > C = NO(-)+H+; pK = 8). The N omega-hydroxyguanidino group is more reactive towards O2-. when deprotonated but exhibits negligible reactivity when protonated. Based on a model, the rate constant for the reaction of the O2-. with NHA was estimated as kappa (O2-.+ > C = NO-) approximately 200-500 M-1.s-1, which is probably too low to compete with O2-. reactions with NO- or superoxide dismutase, which occur many orders of magnitude faster. The oxidative elimination of NO from NHA by O2-. was not accompanied by the formation of L-citrulline. Since only 21% of NHA will exist in the deprotonated > C = NO- form at physiological pH, it is unlikely that oxidative denitrification of NHA by cytochrome P-450 or NOS-derived O2-. radicals will prove a major free-radical pathway to NO. and L-citrulline.

Light-activated Cryptochrome Reacts with Molecular Oxygen to Form a Flavin–Superoxide Radical Pair Consistent with Magnetoreception

“…This indicates that the oxidizing agent in the two cases is not the same. Based on the known reactions of free riboflavin (22), the fate of superoxide in aqueous solutions (23), and the observed redox kinetic behavior of flavin in AtCRY1 described above, we postulate the following reaction schemes.…”

Oxidation of NG‐hydroxyl‐l‐arginine to nitric oxide mediated by respiratory burst: an alternative pathway to NO synthesis

“…Recently, it has been shown that O^ can mediate cleavage of N-hydroxyguanidines resulting in the formation of NO [4]. Moreover, radiolytically induced O^" can cleave OH-Arg [5]; the products of this reaction are NO and a cyclized carbodiimide, without the concomitant formation of citrulline.…”

“…Recently, Sennequier et al have shown that Superoxide anion (OJ) can induce the formation of nitrogen oxides by oxidation of A^-hydroxyguanidines [4]. Furthermore, Everett et al have shown that radiation induced 0^~ mediates denitrification of OH-Arg leading to NO and cyclized carbodiimide [5]. A biological role of this alternative pathway of NO synthesis is suggested by the fact that the intermediate product of enzymatic nitric oxide synthesis, OH-Arg, is elevated in sera of animals treated with LPS [6] and is secreted together with NO in vivo and in vitro, as an adduct [7].…”

Mutation of the Five Conserved Histidines in the Endothelial Nitric-oxide Synthase Hemoprotein Domain

“…The reason for the discrepancy in our findings and those of Perry and Marletta (13) 14 C]citrulline, whereas we determined the production of NO by the hemoglobin assay. The oxidation of guanidoximes such as N-hydroxyarginine is catalyzed by a variety of oxidizing systems, including cytochrome P450 (26), horseradish peroxidase/H 2 O 2 (27), hemoglobin (II), H 2 O 2 alone (28), and superoxide (29,30). This oxidation primarily produces nitrites or nitrates rather than NO.…”