| Pentachlorophenol hydroxylase, a poorly functioning enzyme required for degradation of pentachlorophenol by Sphingobium chlorophenolicum. | |
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MedLine Citation:
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PMID: 22482720 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Several strains of Sphingobium chlorophenolicum have been isolated from soil that was heavily contaminated with pentachlorophenol (PCP), a toxic pesticide introduced in the 1930s. S. chlorophenolicum appears to have assembled a poorly functioning pathway for degradation of PCP by patching enzymes recruited via two independent horizontal gene transfer events into an existing metabolic pathway. Flux through the pathway is limited by PCP hydroxylase. PCP hydroxylase is a dimeric protein that belongs to the family of flavin-dependent phenol hydroxylases. In the presence of NADPH, PCP hydroxylase converts PCP to tetrachlorobenzoquinone (TCBQ). The k(cat) for PCP (0.024 s(-1)) is very low, suggesting that the enzyme is not well evolved for turnover of this substrate. Structure-activity studies reveal that substrate binding and activity are enhanced by a low pK(a) for the phenolic proton, increased hydrophobicity, and the presence of a substituent ortho to the hydroxyl group of the phenol. PCP hydroxylase exhibits substantial uncoupling; the C4a-hydroxyflavin intermediate, instead of hydroxylating the substrate, can decompose to produce H(2)O(2) in a futile cycle that consumes NADPH. The extent of uncoupling varies from 0 to 100% with different substrates. The extent of uncoupling is increased by the presence of bulky substituents at position 3, 4, or 5 and decreased by the presence of a chlorine in the ortho position. The effectiveness of PCP hydroxylase is additionally hindered by its promiscuous activity with tetrachlorohydroquinone (TCHQ), a downstream metabolite in the degradation pathway. The conversion of TCHQ to TCBQ reverses flux through the pathway. Substantial uncoupling also occurs during the reaction with TCHQ. |
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Authors:
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Klara Hlouchova; Johannes Rudolph; Jaana M H Pietari; Linda S Behlen; Shelley D Copley |
Publication Detail:
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Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't Date: 2012-04-27 |
Journal Detail:
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Title: Biochemistry Volume: 51 ISSN: 1520-4995 ISO Abbreviation: Biochemistry Publication Date: 2012 May |
Date Detail:
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Created Date: 2012-05-08 Completed Date: 2012-07-09 Revised Date: 2012-10-23 |
Medline Journal Info:
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Nlm Unique ID: 0370623 Medline TA: Biochemistry Country: United States |
Other Details:
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Languages: eng Pagination: 3848-60 Citation Subset: IM |
Affiliation:
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Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado 80309, USA. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Biodegradation, Environmental Catalysis Hydrogen Peroxide / metabolism Metabolic Networks and Pathways Mixed Function Oxygenases / metabolism* Pentachlorophenol / metabolism* Pesticides / metabolism Sphingomonadaceae / enzymology Structure-Activity Relationship Substrate Specificity |
| Grant Support | |
ID/Acronym/Agency:
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GM078554/GM/NIGMS NIH HHS; R01 GM078554/GM/NIGMS NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Pesticides; 7722-84-1/Hydrogen Peroxide; 87-86-5/Pentachlorophenol; EC 1.-/Mixed Function Oxygenases; EC 1.14.13.50/pentachlorophenol monooxygenase |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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