3- nitrotyrosine

Some work has been completed on reaction of proteins with nitrite followed by hydrolysis and analysis for amino acids It has been shown that 3-nitrotyrosine and 3,4-dihydroxyphenylalanine are formed from bovine serum albumin when nitrosation occurs under conditions similar to those found in the human stomach (36), Direct demonstration that nitrite reacts with protein has been made by using NaN02 with bovine serum albumin (pH 5.5, 20 C and 200 ppm nitrite). A 60% loss of the originally added nitrite was observed in one week and nearly half of the nitrite (labelled %) could be recovered from the protein. Similar work with myosin revealed that 10-20% of the incorporated label was present as 3-nitrotyro-sine (J7). 

An alternative and not necessarily conflicting view is the formation of a free radical at a tyrosine center that was trapped by adding NO to form 3-nitrotyrosine (Zhao et al. 2004). 

Nishino SF, JC Spain (2006) Biodegradation of 3-nitrotyrosine by Burkholderia sp. strain JS165 and Variovo-rax paradoxus JS171. AppZ Environ Microbiol 72 1040-1044. 

Crowley, J.R., Yarasheski, K., Leeuwenburgh, C., Turk, J., and Heinecke, J.W., Isotope dilution mass spectrometric quantification of 3-nitrotyrosine in proteins and tissues is facilitated by reduction to 3-aminotyrosine, Anal. Biochem., 259, 127, 1998. 

Protein tyrosine residues constitute key targets for peroxynitrite-mediated nitrations. Attack of various free radicals (ONOO-, N02 ) upon tyrosine generates 3-nitrotyrosine, which can be measured immunologically or by GC/MS or HPLC techniques. The detection of 3-nitrotyrosine was considered a biomarker of peroxynitrite action in vivo. Similarly, attack of HOC1 and HOBr on tyrosine generates chlorotyro-sine and bromotyrosine, respectively, both of which are measured most accurately by GC-MS. 

Probably, the most convincing proof of free radical mechanism of peroxynitrite reactions is the formation of dityrosine [117,118]. It has been suggested [118] that the nitric dioxide radical is responsible for the formation of both 3-nitrotyrosine and dityrosine (Figure 21.1), however, hydroxyl radicals (which were identified in this system by ESR spectroscopy [119]) may also participate in this process. Pfeiffer et al. [118] proposed that dityrosine is predominantly formed at low fluxes of superoxide and nitric oxide, which corresponds to in vivo conditions, however, this observation was not confirmed by Sawa et al. [117],... 

The reaction of peroxynitrite with the biologically ubiquitous C02 is of special interest due to the presence of both compounds in living organisms therefore, we may be confident that this process takes place under in vivo conditions. After the discovery of this reaction in 1995 by Lymar [136], the interaction of peroxynitrite with carbon dioxide and the reactions of the formed adduct nitrosoperoxocarboxylate ONOOCOO has been thoroughly studied. In 1996, Lymar et al. [137] have shown that this adduct is more reactive than peroxynitrite in the reaction with tyrosine, forming similar to peroxynitrite dityrosine and 3-nitrotyrosine. Experimental data were in quantitative agreement with free radical-mediated mechanism yielding tyrosyl and nitric dioxide radicals as intermediates and were inconsistent with electrophilic mechanism. The lifetime of ONOOCOO was estimated as <3 ms, and the rate constant of Reaction (42) k42 = 2 x 103 1 mol 1 s 1. 

ONOO- + C02 => ONOOCOO ONOOCOO- + tyrosine => dityrosine + 3-nitrotyrosine... 

Similar to peroxynitrite, ONOOCOO- reacts with many biomolecules such as uric acid [110], oxyhemoglobin [133], melatonin [135], NADH, ubiquinol Q0, and glutathione [141], Reactions of ONOOCOO with substrates in mitochondrial matrix is accompanied by protein nitration [141]. The reaction of ONOOCOO- with GSH was so rapid that glutathione inhibited tyrosine nitration by peroxynitrite in the presence of C02 [142], The formation of ONOOCOO- increased the formation of 3-nitrotyrosine and decreased the formation of 3-hydroxytyrosine probably due to the enhanced selectivity of C03 - compared to hydroxyl radicals [143],... 

It has been already pointed out that nitric oxide exhibits antioxidant effect in LDL oxidation at the NO/ 02 ratio 1. Under these conditions the antioxidant effect of NO prevails on the prooxidant effect of peroxynitrite. Although some earlier studies suggested the possibility of NO-mediated LDL oxidation [152,153], these findings were not confirmed [154]. On the other hand, at lower values of N0/02 ratio the formed peroxynitrite becomes an efficient initiator of LDL modification. Beckman et al. [155] suggested that peroxynitrite rapidly reacts with tyrosine residues to form 3-nitrotyrosine. Later on, Leeuwenburgh et al. [156] found that 3-nitrotyrosine was formed in the reaction of peroxynitrite with LDL. The level of 3-nitrotyrosine sharply differed for healthy subjects and patients with cardiovascular diseases LDL isolated from the plasma of healthy subjects contained a very low level of 3-nitrotyrosine (9 + 7 pmol/mol 1 of tyrosine), while LDL isolated from aortic atherosclerotic intima had a 90-fold higher level (840 + 140 pmol/moD1 of tyrosine). It has been proposed that peroxynitrite formed in the human artery wall is able to promote LDL oxidation in vivo. 

An assay for NE, E, L-DOPA, DA, 3-nitrotyrosine, m-,o-, and p-tyrosine compared an amperometric detector with a CoulArray detector. A CoulArray detector has the sensitivity of a coulometric detector applied to eight different electrodes to give an array of applied voltages. A C18 column with a mobile phase consisting of an acetate buffer (pH 4.75) and sodium citrate in methanol was used. The assay was... 

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). 

Peroxynitrite reacts with the active site of superoxide dismutase (SOD) to form a nitronium-like species (Fig. 37), analogous to the Fe EDTA reactions described earlier. However, copper in the active site of superoxide dismutase was necessary for the formation of the adduct. Removing copper from the active site by reduction with borohydride and dialysis against 50 mM KCN resulted in no adduct being formed, while restoration of copper to the active site gave back full enzyme activity. To account for the essential role of copper in the active site and the subsequent formation of 3-nitrotyrosine located 18-21 A distal from the active site, we proposed that peroxynitrite is attracted by the same electrostatic force field that draws superoxide into the active site (Beckman et al., 1992 Ischiropoulos et al., 1992b). Peroxynitrite appears to bind to copper in the active site to form a transient cuprous adduct as shown. 

Hensley, K., Maidt, M. L., Pye, Q. N., Stewart, C. A., Wack, M., Tabatabaie, T., and Floyd, R. A. (1997). Quantitation of protein-bound 3-nitrotyrosine and 3,4-dihydroxy-phenylalanine by high-performance liquid chromatography with electrochemical array detection. Anal. Biochem. 251 187-195. 

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