tailieunhanh - Báo cáo Y học: Exploration of the diaphorase activity of neutrophil NADPH oxidase Critical assessment of the interaction of iodonitrotetrazolium with the oxidase redox components

In the O2– generating flavocytochrome b, the membranebound component of the neutrophil NADPH oxidase, electrons are transported from NADPH to O2 in the following sequence: NADPH fi FAD fi heme b fi O2. Although p-iodonitrotetrazolium (INT) has frequently been used as a probe of the diaphorase activity of the neutrophil flavocytochrome b, the propensity of its radical to interact reversibly with O2 led us to question its specificity. This study was undertaken to reexamine the interaction of INT with the redox components of the neutrophil flavocytochrome b. . | Eur. J. Biochem. 269 1243-1252 2002 FEBS 2002 Exploration of the diaphorase activity of neutrophil NADPH oxidase Critical assessment of the interaction of iodonitrotetrazolium with the oxidase redox components Alexandra Poinas1 Jacques Gaillard2 Pierre Vignais1 and Jacques Doussiere1 1 Laboratoire de Biochimie et Biophysique des Systemes Intégrés UMR 5092 CEA-CNRS Departement de Biologie Moléculaire et Structurale Grenoble France 2Departement de Recherche Fondamentale sur la Matiere Condensee SCIB-SCPM CEA-Grenoble France In the O2- generating flavocytochrome b the membranebound component of the neutrophil NADPH oxidase electrons are transported from NADPH to O2 in the following sequence NADPH FAD heme b O2. Although p-iodonitrotetrazolium INT has frequently been used as a probe of the diaphorase activity of the neutrophil flavocytochrome b the propensity of its radical to interact reversibly with O2 led us to question its specihcity. This study was undertaken to reexamine the interaction of INT with the redox components of the neutrophil flavocytochrome b. Two series of inhibitors were used namely the flavin analog 5-deaza FAD and the heme inhibitors bipyridyl and benzylimidazole. The following results indicate that INT reacts preferentially with the hemes rather than with the FAD redox center of flavocytochrome b and is not therefore a specific probe of the diaphorase activity of flavocyto- chrome b. First in anaerobiosis reduced heme b in activated membranes was reoxidized by INT as efficiently as by O2 even in the presence of concentrations of 5-deaza FAD which fully inhibited the NADPH oxidase activity. Second the titration curve of dithionite-reduced heme b in neutrophil membranes obtained by oxidation with increasing amounts of INT was strictly superimposable on that of dithionite-reduced hemin. Third INT competitively inhibited the O2 uptake by the activated NADPH oxidase in a cell-free system. Finally the heme inhibitor bipyridyl competitively inhibited .

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