Abstract
The reaction between reactive nitrogen species (RNSs) such as peroxynitrite and nitrogen oxide (NOx), and aromatic amino acids such as tyrosine and tryptophan results in a number of modifications, of which tyrosine nitration has gained much attention. 3-Nitrotyrosine (3-NT) was considered as an important biomarker of nitrative stress in vivo. In this work, the reaction rate constants of 3-NT, N-acetyl-3-nitrotyrosine ethyl ester (NANTE ) and 3-NT containing peptide Gly-nitroTyr-Gly reacting with azide radical (N3•) at pH 6.0 were measured as 9.8±0.7x108, 8.0±0.4x108 and 9.1±1.0x108 [L mol-1 s-1], respectively, which were almost one order magnitude higher than that of tyrosine and tyrosine containing peptides. The UV-visible absorption spectra of the transients of N3• reacting with the above compounds were also investigated, bands of the transients located at a wavelength around 415 nm, which showed characteristic of tyrosyl radical. The absorption of the transients was pH dependent. Radiation-induced dimerization of 3-NT and N-acetyl-3-nitrotyrosine ethyl ester were identified and investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MSn). The results implied the possibility of protein aggregation through covalent dimerization of 3-NT residue in vivo.
