Abstract
The complete macro- and microequilibrium analyses of 3-nitrotyrosine, a biomarker of oxidative stress damage, are presented for the first time. The protonation macroconstants were determined by 1 H-NMR-pH titration, while microconstants were elucidated by a combination of deductive and NMR methods, in which properties of the methyl ester derivative as an auxiliary compound were also studied. Combination of the NMR-pH characterization of the title and auxiliary compounds and the pair-interactivity parameters of 3-iodotyrosine provided the sufficient system to evaluate all the microconstants. NMR-pH profiles, macroscopic and microscopic protonation schemes, and species-specific distribution diagrams are included. The phenolate basicity of 3-nitrotyrosine is 500 times below that of tyrosine, and it is even lower than that of 3-iodotyrosine. This phenomenon can be explained by the stronger electron withdrawing and the negative mesomeric effect of the nitro group. Based on our results, 89 % of the phenolic OH groups are deprotonated in 3-NT molecules at the pH of the blood plasma.
Highlights
3-Nitrotyrosine (3-NT, Figure 1) is the earliest discovered biomarker of nitrosative stress
The protonation macroconstants were determined by 1H-NMR-pH titration, while microconstants were elucidated by a combination of deductive and NMR methods, in which properties of the methyl ester derivative as an auxiliary compound were studied
*NO2 is responsible for solvent-exposed Tyr nitration, while transition metals can lead to nitration of buried Tyr residues.[1]
Summary
3-Nitrotyrosine (3-NT, Figure 1) is the earliest discovered biomarker of nitrosative stress It is formed through the nitration of tyrosine (Tyr) by peroxynitrite. At low pH, 3-NT is more hydrophobic than Tyr, while at high pH, it is more polar than Tyr.[4,5] Tyr nitration obviously alters the protein structures and concomitantly the physiological effects. These modifications are strongly related to diseases, mainly with degenerative and inflammatory symptoms. The site-specific acid-base characterization of 3-NT is of fundamental importance to allow the interpretation of its biological functions at site-specific level
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