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Proteasa, G., Tahboub, Y., Galijasevic, S., Russel, F. and Abu-Soud, H. (2007) kinetic evidence supports the existence of two halide binding sites that have a distinct impact on the heme microenvironment of myeloperoxidase. Biochemistry, 46, 398-405. doi:10.1021/bi0609725

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• TITLE: A predictive kinetic model for inhibitory effect of nitrite on myeloperoxidase catalytic activity towards oxidation of chloride

  AUTHORS: Yahya R. Tahboub, Mohammad M. Fares

  KEYWORDS: MPO-Hydrogen Peroxide-Chloride System; Nitrite Inhibitor; k4/k3, k4/k2, and k2/k3 Ratios; Theoretical Kinetic model

  JOURNAL NAME: Journal of Biophysical Chemistry, Vol.2 No.3, August 11, 2011

  ABSTRACT: Myeloperoxidase (MPO) is a neutrophil enzyme that employs hydrogen peroxide (H2O2) to catalyze the oxidation of chloride (Cl–) to hypochlorous acid (HOCl). Accepted mechanism is based on rapid reaction of native MPO with H2O2to produce Compound I (MPO-I) which oxidizes Cl– through a 2e– transition generating MPO and HOCl. MPO-I also reacts with H2O2 to generate Compound II (MPO-II) which is inactive in 2e oxidation of Cl–. Nitrite ( NO2-) inhibits the 2e oxidation of Cl– by reaction with MPO-I through 1e transition generating MPO-II and nitrite radical. H2O2 consumption during steady- state catalysis was monitored amperometrically by a carbon fiber based H2O2-biosensor at 25oC. Results demonstrated that in absence of NO2- reactions were monophasic and rapid (complete H2O2 consumption occurs in 2- increases, reactions change to biphasic (rapid step followed by a slow step) and both steps have been inhibited by NO2- . A predictive kinetic model describing the inhibittory effect of NO2- was developed and applied to experimental results The model is based on the assumption that MPO–I cannot be detected during steady-state catalysis. Calculated rate constants are in agreement with those obtained from pre-steady state kinetic methods.