The Heme Component of the Neutrophil NADPH Oxidase Complex Is a Target for Aryliodonium Compounds

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• 作者：Jacques Doussiere ; Jacques Gaillard ; and Pierre V. Vignais
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：March 23, 1999
• 年：1999
• 卷：38
• 期：12
• 页码：3694 - 3703
• 全文大小：147K
• 年卷期：v.38,no.12(March 23, 1999)
• ISSN：1520-4995

文摘

The redox core of the neutrophil NADPH oxidase complex is a membrane-bound flavocytochrome b in which FAD and heme b are the two prosthetic redox groups. Both FAD and heme b are ableto react with diphenylene iodonium (DPI) and iodonium biphenyl (IBP), two inhibitors of NADPH oxidaseactivity. In this study, we show that the iodonium modification of heme b contributes predominantly tothe inhibition of NADPH oxidase. This conclusion is based on the finding that both iodonium compoundsdecreased the absorbance of the Soret peak of flavocytochrome b in neutrophil membranes incubatedwith NADPH, and that this decrease was strictly correlated with the loss of oxidase activity. Furthermore,the heme component of purified flavocytochrome b reduced to no more than 95% by a limited amount ofsodium dithionite could be oxidized by DPI or IBP. Butylisocyanide which binds to heme iron precludesheme b oxidation. In activated neutrophil membranes, competitive inhibition of O₂ uptake by DPI or IBPoccurred transiently and was followed by a noncompetitive inhibition. These results, together with thoseof EPR spectroscopy experiments, lead us to postulate that DPI or IBP first captures an electron from thereduced heme iron of flavocytochrome b to generate a free radical. Then, the binding of this radical to theproximate environment of the heme iron, most probably on the porphyrin ring, results in inhibition ofoxidase activity. In the presence of an excess of sodium dithionite, DPI and IBP produced a biphasicdecrease of the Soret band of flavocytochrome b, with a break in the dose effect curve occurring at 50%of the absorbance loss. This was consistent with the presence of two hemes in flavocytochrome b thatdiffer by their sensitivity to DPI or IBP.