Abstract

TAHBOUB, Yahya R.  and  ABU-SOUD, Husam M.. Steady-State Study of Inhibitory Effect of Nitrite on Myeloperoxidase Catalytic Activity by Hydrogen Peroxide Biosensor. Port. Electrochim. Acta [online]. 2010, vol.28, n.1, pp.27-38. ISSN 0872-1904.

Myeloperoxidase (MPO) is a neutrophil enzyme that employs hydrogen peroxide (H₂O₂) to catalyze the oxidation of halides and thiocyanate to their respective hypohalous acids. In this study, the inhibitory effect of nitrite (NO₂^-) on MPO-catalytic activity was investigated electrochemically. H₂O₂ consumption during steady-state catalysis was monitored amperometrically by a carbon fiber based H₂O₂-biosensor at 25 ^oC. Optimized initial concentrations were 50 nM MPO, 10 μM H₂O₂, and a selected halide or thiocyanate concentration from physiological range. Under these conditions, reactions were monophasic and rapid (complete H₂O₂ consumption occurs in < 10 s). As concentration of NO₂^- increases, reactions change to biphasic (rapid step followed by a slow step) and both steps have been inhibited by NO₂^-. Our results confirmed the inhibitory effect of NO₂^- and demonstrated for the first time that NO₂^- is a strong inhibitor towards MPO-catalyzed oxidation of iodide and bromide; and a weak inhibitor towards MPO-catalyzed oxidation of chloride and thiocyanate.

Keywords : nitric oxide; nitrite; myeloperoxidase; catalytic activity; H₂O₂-biosensor.

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