| 11437359 |
Reddy GV, Gold MH: Purification and characterization of glutathione conjugate reductase: a component of the tetrachlorohydroquinone reductive dehalogenase system from Phanerochaete chrysosporium. Arch Biochem Biophys. 2001 Jul 15;391(2):271-7.
A membrane-bound glutathione S-transferase and a soluble glutathione conjugate reductase constitute the reductive dehalogenase system of P. chrysosporium. This enzyme system reductively removes chlorine substituents from tetrachlorohydroquinone, a metabolite of pentachlorophenol. The membrane-bound glutathione S-transferase converts tetrachlorohydroquinone to S-glutathionyltrichloro-1,4-hydroquinone, which is subsequently reduced to 3,5,6-trichlorohydroquinone by the soluble glutathione conjugate reductase (GCR). This GCR can accept glutathione, dithiothreitol, cysteine, or beta-mercaptoethanol as cosubstrates. GCR was purified to apparent homogeneity by ion-exchange and covalent chromatography. The enzyme exhibits optimum activity at pH 6.0 and 55 degrees C and appears to be a homodimer with a M (r) of approximately 60 kDa. Activity increases as the number of chlorine substituents on the hydroquinone ring is increased. GCR has an apparent K (m) of approximately 33 microM and an apparent k (cat) of approximately 3.43 s (-1) for 2-S-glutathionyl-3,5,6-trichloro-1,4-hydroquinone. Inhibitors of GCR include Cd (2+), Fe (2+), Mn (2+), iodoacetic acid, and p-chloromercuribenzoic acid, suggesting the presence of a catalytic cysteine thiol (s) at the active site. When glutathione is used as a cosubstrate, reduction of S-glutathionyltrichloro-1,4-hydroquinone is accompanied by the production of trichlorohydroquinone and oxidized glutathione in a 1:1 ratio. A mechanism for this novel enzyme is proposed. |
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