title: A bacterial flavin reductase system reduces chromate to a soluble chromium(III)-NAD(+) complex.
abstract: Biological reduction of carcinogenic chromate has been extensively studied in eukaryotic cells partly because the reduction produces stable chromium(III)-DNA adducts, which are mutagenic. Microbial reduction of chromate has been studied for bioremediation purposes, but little is known about the reduction mechanism. In eukaryotic cells chromate is mainly reduced non-enzymatically by ascorbate, which is usually absent in bacterial cells. We have characterized the reduction of chromate by a flavin reductase (Fre) from Escherichia coli with flavins. The Fre-flavin system rapidly reduced chromate, whereas chemical reduction by NADH and glutathione was very slow. Thus, enzymatic chromate reduction is likely the dominant mechanism in bacterial cells. Furthermore, the end-product was a soluble and stable Cr(III)-NAD(+) complex, instead of Cr(III) precipitate. Since intracellularly generated Cr(III) forms adducts with DNA, protein, glutathione, and ascorbate in eukaryotic cells, we suggest that the produced Cr(III) is primarily complexed to NAD(+), DNA, and other cellular components inside bacteria.
authors.affiliation: School of Molecular Biosciences, Washington State University, Pullman, WA 99164-4234, USA.
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Puzon
authors.forename: James N
authors.initials: JN
authors.lastname: Petersen
authors.forename: Arthur G
authors.initials: AG
authors.lastname: Roberts
authors.forename: David M
authors.initials: DM
authors.lastname: Kramer
authors.forename: Luying
authors.initials: L
authors.lastname: Xun
mesh_terms: D002840:Chromates / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology; D038181:FMN Reductase; D009243:NAD / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D013054:Spectrophotometry, Atomic
chemical_list: D002840:Chromates; D009243:NAD; D038181:FMN Reductase; D009247:NADH, NADPH Oxidoreductases