Nitration and Hydroxylation by Peroxynitrite

Peroxynitrite (ONOO ) is a cytoxic species that is considered to form nitric oxide (NO) and superoxide (Oj ) in biological systems (Beckman et al. 1990). The toxicity of this compound is attributed to its ability to oxidize, nitrate, and hydroxylate biomolecules. Tyrosine is nitrated to form 3-nitrotyrosine (Ramazanian et al. 1996). Phenylalanine is hydroxylated to yield o-, m-, and p-tyrosines. Cysteine is oxidized to give cystine (Radi et al. 1991a). Glutathione is converted to S-nitro- or S-nitroso derivatives (Balazy et al. 1998). Catecholamines are oxidatively polymerized to melanin (Daveu et al. 1997). Lipids are also oxidized (Radi 1991b) and DNA can be scissored by peroxynitrite (Szabo and Ohshima 1997). 

Despite a considerable literature on the various modes of reactions induced by peroxynitrite, the kinetic and mechanistic aspects of these transformations have been clarified only recently (Nonoyama et al. 1999). The authors give the following picture of the peroxynitrite chemical behavior. In alkaline solutions, peroxynitrite is a stable anionic species. At physiological pH, it is rapidly protonated to form peroxynitrous acid (ONOOH) ONOO -I- H ONOOH. 

This acid undergoes homolytic decomposition to OH and N02 radical species  

Heterolytic decomposition of the acid is also possible Pryor and Squadrito (1995) connect this direction with the generation of a high-energy intermediate [ONOOH] N02 + OH — [ONOOH] NO + OOH. Interactions between such generated species eventually lead to the formation of NO and NO3 ions  

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