TAILIEUCHUNG - Báo cáo khóa học: Mechanistic insight into the peroxidase catalyzed nitration of tyrosine derivatives by nitrite and hydrogen peroxide

Peroxidases perform the nitration of tyrosine and tyrosyl residues in proteins, in the presence of nitrite and hydrogen peroxide. The nitrating species is still unknown but it is usually assumed to be nitrogen dioxide. In the present investigation, the nitration of phenolic compounds derived from tyrosine by lactoperoxidase and horseradish peroxi-dasewas studied, with the aimof elucidating themechanism of the reaction. | Eur. J. Biochem. 271 895-906 2004 FEBS 2004 doi Mechanistic insight into the peroxidase catalyzed nitration of tyrosine derivatives by nitrite and hydrogen peroxide Enrico Monzani1 Raffaella Roncone1 Monica Galliano2 Willem H. Koppenol3 and Luigi Casella1 1 Dipartimento di Chimica Generale 2Dipartimento di Biochimica Universita di Pavia Italy 3Institute of Inorganic Chemistry ETH Honggerberg Zurich Switzerland Peroxidases perform the nitration of tyrosine and tyrosyl residues in proteins in the presence of nitrite and hydrogen peroxide. The nitrating species is still unknown but it is usually assumed to be nitrogen dioxide. In the present investigation the nitration of phenolic compounds derived from tyrosine by lactoperoxidase and horseradish peroxidase was studied with the aim of elucidating the mechanism of the reaction. The results indicate that nitrogen dioxide cannot be the only nitrating species and suggest the presence of two simultaneously operative pathways one proceeding through enzyme-generated nitrogen dioxide and another through a more reactive species assumed to be complexed peroxynitrite which is generated by reaction of hydrogen peroxide with the enzyme-nitrite complex. The importance of the two pathways depends on peroxide and nitrite concentrations. With lactoperoxidase nitration through the highly reactive intermediate is preferred except at very low nitrite concentration while with horseradish peroxidase the nitrogen dioxide driven mechanism is preferred except at very high nitrite concentration. The preferred mechanism for the two enzymes is that operative in the physiological nitrite concentration range. Keywords nitrogen dioxide peroxidases peroxynitrite phenol nitration reactive nitrogen species. It is well documented that reactive nitrogen species derived from nitrogen monoxide NO are involved in many pathological conditions 1 2 . Although NO performs many important physiological functions ranging from .

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