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Journal of Bacteriology, April 2000, p. 2238-2244, Vol. 182, No. 8
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Second [2Fe-2S] Ferredoxin from Sphingomonas sp. Strain RW1 Can Function as an Electron Donor for the Dioxin Dioxygenase

Jean Armengaud,1,2,* Jacques Gaillard,3 and Kenneth N. Timmis1

Division of Microbiology, GBF-National Research Center for Biotechnology, D-38124 Braunschweig, Germany,1 and Institut de Biologie Structurale, IBS-LSMP, F-38027 Grenoble Cedex 1,2 and Départment de Recherche Fondamentale sur la Matière Condensée/SCIB/SCPM, Commissariat à l'Energie Atomique---Grenoble, 38054 Grenoble Cedex 9,3 France

Received 13 October 1999/Accepted 13 January 2000

The first step in the degradation of dibenzofuran and dibenzo-p-dioxin by Sphingomonas sp. strain RW1 is carried out by dioxin dioxygenase (DxnA1A2), a ring-dihydroxylating enzyme. An open reading frame (fdx3) that could potentially specify a new ferredoxin has been identified downstream of dxnA1A2, a two-cistron gene (J. Armengaud, B. Happe, and K. N. Timmis, J. Bacteriol. 180:3954-3966, 1998). In the present study, we report a biochemical analysis of Fdx3 produced in Escherichia coli. This third ferredoxin thus far identified in Sphingomonas sp. strain RW1 contained a putidaredoxin-type [2Fe-2S] cluster which was characterized by UV-visible absorption spectrophotometry and electron paramagnetic resonance spectroscopy. The midpoint redox potential of this ferredoxin (E'0 = -247 ± 10 mV versus normal hydrogen electrode at pH 8.0) is similar to that exhibited by Fdx1 (-245 mV), a homologous ferredoxin previously characterized in Sphingomonas sp. strain RW1. In in vitro assays, Fdx3 can be reduced by RedA2 (a reductase similar to class I cytochrome P-450 reductases), previously isolated from Sphingomonas sp. strain RW1. RedA2 exhibits a Km value of 3.2 ± 0.3 µM for Fdx3. In vivo coexpression of fdx3 and redA2 with dxnA1A2 confirmed that Fdx3 can serve as an electron donor for the dioxin dioxygenase.

* Corresponding author. Mailing address: Institut de Biologie Structurale, IBS-LSMP, 41 Rue Jules Horowitz, F-38027 Grenoble Cedex 1, France. Phone: (33) 4 76 88 30 37. Fax: (33) 4 76 88 54 94. E-mail: jean.armengaud{at}ibs.fr.

Journal of Bacteriology, April 2000, p. 2238-2244, Vol. 182, No. 8
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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