Evidence for the Saccharomyces cerevisiae ferrireductase system being a multicomponent electron transport chain.
We have studied the relationships between in vivo (whole cells) and in vitro (plasma membranes) ferrireductase activity in Saccharomyces cerevisiae. Isolated plasma membranes were enriched in the product of the FRE1 gene and had NADPH dehydrogenase activity that was increased when the cells were grown in iron/copper-deprived medium. The diaphorase activity was, however, independent of Fre1p, and Fre1p itself had no ferrireductase activity in vitro. There were striking similarities between the yeast ferrireductase system and the neutrophil NADPH oxidase: oxygen could act as an electron acceptor in the ferrireductase system, and Fre1p, like gp91, is a glycosylated hemoprotein with a b-type cytochrome spectrum. The ferrireductase system was sensitive to the NADPH oxidase inhibitor diphenylene iodonium (DPI). DPI inhibition proceeded with two apparent Ki values (high and low affinity binding) in whole wild-type and Deltafre2 cells and with one apparent Ki in Deltafre1 cells (high affinity binding) and in plasma membranes (low affinity binding). These results suggest that the Fre1-dependent ferrireductase system involves at least two components (Fre1p and an NADPH dehydrogenase component) differing in their sensitivities to DPI, as in the neutrophil NADPH oxidase. A third component, the product of the UTR1 gene, was shown to act synergistically with Fre1p to increase the cell ferrireductase activity.
Lesuisse
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Laboratoire de Biochimie des Porphyrines, Institut Jacques Monod, Tour 43, Université Paris 7, 2 Place Jussieu, 75251 Paris Cedex 05, France.
Casteras-Simon
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Labbe
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D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D003902:Detergents / Q000494:pharmacology; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038181:FMN Reductase; D005290:Ferric Compounds / Q000378:metabolism; D005800:Genes, Fungal; D007700:Kinetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000201:enzymology; D009861:Onium Compounds / Q000494:pharmacology; D010078:Oxazines / Q000378:metabolism; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014966:Xanthenes
D003902:Detergents; D004791:Enzyme Inhibitors; D005290:Ferric Compounds; D009861:Onium Compounds; D010078:Oxazines; D014966:Xanthenes; D013481:Superoxides; C005843:resazurin; C025314:ferric citrate; C007517:diphenyleneiodonium; D038181:FMN Reductase; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; C023903:ferric citrate iron reductase