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Coleman T, Podgorski MN, Doyle ML, Scaffidi-Muta JM, Campbell EC, Bruning JB, De Voss JJ, Bell SG. Cytochrome P450-catalyzed oxidation of halogen-containing substrates. J Inorg Biochem 2023; 244:112234. [PMID: 37116269 DOI: 10.1016/j.jinorgbio.2023.112234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Revised: 04/15/2023] [Accepted: 04/15/2023] [Indexed: 04/30/2023]
Abstract
Cytochrome P450 (CYP) enzymes are heme-thiolate monooxygenases which catalyze the oxidation of aliphatic and aromatic C-H bonds and other reactions. The oxidation of halogens by cytochrome P450 enzymes has also been reported. Here we use CYP199A4, from the bacterium Rhodopseudomonas palustris strain HaA2, with a range of para-substituted benzoic acid ligands, which contain halogens, to assess if this enzyme can oxidize these species or if the presence of these electronegative atoms can alter the outcome of P450-catalyzed reactions. Despite binding to the enzyme, there was no detectable oxidation of any of the 4-halobenzoic acids. CYP199A4 was, however, able to efficiently catalyze the oxidation of both 4-chloromethyl- and 4-bromomethyl-benzoic acid to 4-formylbenzoic acid via hydroxylation of the α‑carbon. The 4-chloromethyl substrate bound in the enzyme active site in a similar manner to 4-ethylbenzoic acid. This places the benzylic α‑carbon hydrogens in an unfavorable position for abstraction indicating a degree of substrate mobility must be possible within the active site. CYP199A4 catalyzed oxidations of 4-(2'-haloethyl)benzoic acids yielding α-hydroxylation and desaturation metabolites. The α-hydroxylation product was the major metabolite. The desaturation pathway is significantly disfavored compared to 4-ethylbenzoic acid. This may be due to the electron-withdrawing halogen atom or a different positioning of the substrate within the active site. The latter was demonstrated by the X-ray crystal structures of CYP199A4 with these substrates. Overall, the presence of a halogen atom positioned close to the heme iron can alter the binding orientation and outcomes of enzyme-catalyzed oxidation.
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Affiliation(s)
- Tom Coleman
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia
| | | | - Maya L Doyle
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia
| | | | - Eleanor C Campbell
- Australian Synchrotron, 800 Blackburn Rd, Clayton, Melbourne, VIC 3168. Australia
| | - John B Bruning
- School of Biological Sciences, University of Adelaide, Adelaide, SA 5005, Australia
| | - James J De Voss
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
| | - Stephen G Bell
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia.
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Behrendorff JBYH. Reductive Cytochrome P450 Reactions and Their Potential Role in Bioremediation. Front Microbiol 2021; 12:649273. [PMID: 33936006 PMCID: PMC8081977 DOI: 10.3389/fmicb.2021.649273] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 03/22/2021] [Indexed: 11/13/2022] Open
Abstract
Cytochrome P450 enzymes, or P450s, are haem monooxygenases renowned for their ability to insert one atom from molecular oxygen into an exceptionally broad range of substrates while reducing the other atom to water. However, some substrates including many organohalide and nitro compounds present little or no opportunity for oxidation. Under hypoxic conditions P450s can perform reductive reactions, contributing electrons to drive reductive elimination reactions. P450s can catalyse dehalogenation and denitration of a range of environmentally persistent pollutants including halogenated hydrocarbons and nitroamine explosives. P450-mediated reductive dehalogenations were first discovered in the context of human pharmacology but have since been observed in a variety of organisms. Additionally, P450-mediated reductive denitration of synthetic explosives has been discovered in bacteria that inhabit contaminated soils. This review will examine the distribution of P450-mediated reductive dehalogenations and denitrations in nature and discuss synthetic biology approaches to developing P450-based reagents for bioremediation.
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Affiliation(s)
- James B. Y. H. Behrendorff
- Centre for Agriculture and the Bioeconomy, Queensland University of Technology, Brisbane, QLD, Australia
- Commonwealth Scientific and Industrial Research Organisation (CSIRO) Synthetic Biology Future Science Platform, Canberra, ACT, Australia
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Deda DK, Iglesias BA, Alves E, Araki K, Garcia CRS. Porphyrin Derivative Nanoformulations for Therapy and Antiparasitic Agents. Molecules 2020; 25:molecules25092080. [PMID: 32365664 PMCID: PMC7249045 DOI: 10.3390/molecules25092080] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 04/21/2020] [Accepted: 04/22/2020] [Indexed: 12/12/2022] Open
Abstract
Porphyrins and analogous macrocycles exhibit interesting photochemical, catalytic, and luminescence properties demonstrating high potential in the treatment of several diseases. Among them can be highlighted the possibility of application in photodynamic therapy and antimicrobial/antiparasitic PDT, for example, of malaria parasite. However, the low efficiency generally associated with their low solubility in water and bioavailability have precluded biomedical applications. Nanotechnology can provide efficient strategies to enhance bioavailability and incorporate targeted delivery properties to conventional pharmaceuticals, enhancing the effectiveness and reducing the toxicity, thus improving the adhesion to the treatment. In this way, those limitations can be overcome by using two main strategies: (1) Incorporation of hydrophilic substituents into the macrocycle ring while controlling the interaction with biological systems and (2) by including them in nanocarriers and delivery nanosystems. This review will focus on antiparasitic drugs based on porphyrin derivatives developed according to these two strategies, considering their vast and increasing applications befitting the multiple roles of these compounds in nature.
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Affiliation(s)
- Daiana K. Deda
- Department of Fundamental Chemistry, Institute of Chemistry, University of Sao Paulo, Av. Prof. Lineu Prestes 748, Butanta, Sao Paulo, SP 05508-000, Brazil; (D.K.D.); (K.A.)
| | - Bernardo A. Iglesias
- Bioinorganic and Porphyrinoid Materials Laboratory, Department of Chemistry, Federal University of Santa Maria, Av. Roraima 1000, Camobi, Santa Maria, RS 97105-900, Brazil;
| | - Eduardo Alves
- Department of Life Science, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, UK;
| | - Koiti Araki
- Department of Fundamental Chemistry, Institute of Chemistry, University of Sao Paulo, Av. Prof. Lineu Prestes 748, Butanta, Sao Paulo, SP 05508-000, Brazil; (D.K.D.); (K.A.)
| | - Celia R. S. Garcia
- Department of Clinical and Toxicological Analyses, School of Pharmaceutical Sciences, University of Sao Paulo, Av. Prof. Lineu Prestes, 580, Sao Paulo, SP 05508-900, Brazil
- Correspondence: ; Tel.: +55-11-2648-0954
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Yoshikawa M, Zhang M, Toyota K. Biodegradation of Volatile Organic Compounds and Their Effects on Biodegradability under Co-Existing Conditions. Microbes Environ 2017; 32:188-200. [PMID: 28904262 PMCID: PMC5606688 DOI: 10.1264/jsme2.me16188] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Volatile organic compounds (VOCs) are major pollutants that are found in contaminated sites, particularly in developed countries such as Japan. Various microorganisms that degrade individual VOCs have been reported, and genomic information related to their phylogenetic classification and VOC-degrading enzymes is available. However, the biodegradation of multiple VOCs remains a challenging issue. Practical sites, such as chemical factories, research facilities, and illegal dumping sites, are often contaminated with multiple VOCs. In order to investigate the potential of biodegrading multiple VOCs, we initially reviewed the biodegradation of individual VOCs. VOCs include chlorinated ethenes (tetrachloroethene, trichloroethene, dichloroethene, and vinyl chloride), BTEX (benzene, toluene, ethylbenzene, and xylene), and chlorinated methanes (carbon tetrachloride, chloroform, and dichloromethane). We also summarized essential information on the biodegradation of each kind of VOC under aerobic and anaerobic conditions, together with the microorganisms that are involved in VOC-degrading pathways. Interactions among multiple VOCs were then discussed based on concrete examples. Under conditions in which multiple VOCs co-exist, the biodegradation of a VOC may be constrained, enhanced, and/or unaffected by other compounds. Co-metabolism may enhance the degradation of other VOCs. In contrast, constraints are imposed by the toxicity of co-existing VOCs and their by-products, catabolite repression, or competition between VOC-degrading enzymes. This review provides fundamental, but systematic information for designing strategies for the bioremediation of multiple VOCs, as well as information on the role of key microorganisms that degrade VOCs.
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Affiliation(s)
- Miho Yoshikawa
- Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST).,Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology
| | - Ming Zhang
- Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)
| | - Koki Toyota
- Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology
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Cui D, Cabalu T, Yee KL, Small J, Li X, Liu B, Maciolek C, Smith S, Liu W, McCrea JB, Prueksaritanont T. In vitro and in vivo characterisation of the metabolism and disposition of suvorexant in humans. Xenobiotica 2016; 46:882-95. [PMID: 26864332 DOI: 10.3109/00498254.2015.1129565] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
1. Suvorexant (MK-4305, Belsomra®) is a first-in-class dual orexin receptor antagonist approved in the USA and Japan for the treatment of insomnia. The current studies describe suvorexant's absorption, disposition and potential for CYP-mediated drug interactions in humans. 2. Following single oral administration of [(14)C]suvorexant to healthy human subjects, 90% of the radioactivity was recovered (66% in faeces, 23% in urine), primarily as oxidative metabolites. 3. In plasma, suvorexant and M9 were predominant, accounting for 30 and 37% of the total radioactivity, respectively. Metabolite M17 became more prominent (approaching 10%) following multiple daily doses of unlabelled suvorexant. M9 and M17 are not expected to contribute to the pharmacological activity of suvorexant due to reduced orexin receptor binding affinity and limited brain penetration. 4. CYP3A was determined to be the predominant enzyme mediating suvorexant oxidation. In vitro, suvorexant demonstrated reversible inhibition of CYP3A4 and 2C19 (IC50 ∼ 4-5 μM), and weak time-dependent inhibition of CYP3A4 (KI = 12 μM, kinact = 0.14 min(-1)). Suvorexant was also a weak inducer of CYP3A4, 1A2 and 2B6. Given the low plasma concentrations at clinical doses, suvorexant was not anticipated to cause significant drug interactions via inhibition and/or induction of major CYPs in vivo.
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Affiliation(s)
- Donghui Cui
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Tamara Cabalu
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Ka Lai Yee
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - James Small
- b Structure Elucidation NMR Group, Process Chemistry, Merck & Co, Inc , West Point , PA , USA
| | - Xiaodong Li
- c Bristol-Myers Squibb, Full Development Statistics, Global Biometrics Science , Hopewell , NJ , USA , and
| | - Bo Liu
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Cheri Maciolek
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Sheri Smith
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Wen Liu
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
| | - Jacqueline B McCrea
- d Department of Clinical Pharmacology and Experimental Therapeutics (CPET) , Merck & Co, Inc , Kenilworth , NJ , USA
| | - Thomayant Prueksaritanont
- a Department of Pharmacokinetics , Pharmacodynamics and Drug Metabolism, Merck & Co, Inc , West Point , PA , USA
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Iwakiri R, Yoshihira K, Futagami T, Goto M, Furukawa K. Total Degradation of Pentachloroethane by an EngineeredAlcaligenesStrain Expressing a Modified Camphor Monooxygenase and a Hybrid Dioxygenase. Biosci Biotechnol Biochem 2014; 68:1353-6. [PMID: 15215602 DOI: 10.1271/bbb.68.1353] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We engineered biphenyl-degrading Alcaligenes sp. strain KF711 for total degradation of pentachloroethane (PCA), which expresses a modified camphor monooxygenase and a hybrid dioxygenase consisting of TodC1 (a large subunit of toluene dioxygenase of Pseudomonas putida F1) and BphA2-BphA3-pbhA4 (a small subunit, ferredoxin and ferredoxin reductase of biphenyl dioxygenase, respectively, in strain KF707). Modified camphor monooxygenase genes (camCAB) were supplied as a plasmid and the todC1 gene was integrated within the chromosomal bph gene cluster by a single crossover recombination. The resultant strain KF711S-3cam dechlorinated PCA to trichloroethene by the action of the modified camphor monooxygenase under anaerobic conditions. The same strain subsequently degraded trichloroethene formed oxidatively by the action of the Tol-Bph hybrid dioxygenase under aerobic conditions. Thus sequential anaerobic and aerobic treatments of the KF711S-3cam resting cells resulted in efficient and total degradation of PCA.
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Affiliation(s)
- Ryo Iwakiri
- Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Fukuoka, Japan
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Li XX, Zheng QC, Wang Y, Zhang HX. Theoretical insights into the reductive metabolism of CCl4 by cytochrome P450 enzymes and the CCl4-dependent suicidal inactivation of P450. Dalton Trans 2014; 43:14833-40. [DOI: 10.1039/c4dt02065k] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The one-electron reduction product, ˙CCl3, irreversibly inactivates P450 via covalently binding to the meso-carbon, whereas the two successive one-electron reductions product, :CCl2, reversibly inhibits P450 by coordinating to iron.
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Affiliation(s)
- Xiao-Xi Li
- State Key Laboratory of Theoretical and Computational Chemistry
- Institute of Theoretical Chemistry
- Jilin University
- Changchun 130023, People's Republic of China
- Dalian Institute of Chemical Physics
| | - Qing-Chuan Zheng
- State Key Laboratory of Theoretical and Computational Chemistry
- Institute of Theoretical Chemistry
- Jilin University
- Changchun 130023, People's Republic of China
| | - Yong Wang
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
- Dalian 116023, People's Republic of China
| | - Hong-Xing Zhang
- State Key Laboratory of Theoretical and Computational Chemistry
- Institute of Theoretical Chemistry
- Jilin University
- Changchun 130023, People's Republic of China
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Zhao Y, Fan K, Huang Y, Zheng X. Matrix isolation infrared spectra, assignment and DFT investigation on reactions of iron and manganese monoxides with CH3Cl. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2013; 116:96-101. [PMID: 23912047 DOI: 10.1016/j.saa.2013.07.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/27/2013] [Accepted: 07/02/2013] [Indexed: 06/02/2023]
Abstract
The reactions of iron and manganese monoxide molecules (FeO, and MnO) with monochloromethane in solid argon have been studied by matrix isolation infrared spectroscopy and quantum chemistry calculations. When annealing, the reactions of FeO and MnO with CH3Cl first form the OM-(η(Cl)-CH3Cl) (MMn, Fe) complexes, which can isomerize to CH3MOCl (MMn, Fe) upon 300<λ<580 nm irradiation. The products were characterized by isotopic IR studies with CD3Cl and (13)CH3Cl and density functional calculations. Based on theoretical calculations, the OFe-(η(Cl)-CH3Cl) and OMn-(η(Cl)-CH3Cl) complexes have (5)A' and (6)A' ground state with Cs symmetry, respectively. The accurate CCSD(T) single point calculations illustrate the CH3MOCl isomerism are 13.8 and 3.1 kcal/mol lower in energy than the OM-(η(Cl)-CH3Cl) (MMn, Fe) complexes.
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Affiliation(s)
- Yanying Zhao
- Department of Chemistry, Engineering Research Center for Eco-dyeing and Finishing of Textiles, Key Laboratory of Advanced Textiles Materials and Manufacture Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, China.
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Koenig JC, Lee MJ, Manefield M. Successful microcosm demonstration of a strategy for biodegradation of a mixture of carbon tetrachloride and perchloroethene harnessing sulfate reducing and dehalorespiring bacteria. JOURNAL OF HAZARDOUS MATERIALS 2012; 219-220:169-175. [PMID: 22503214 DOI: 10.1016/j.jhazmat.2012.03.076] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 03/05/2012] [Accepted: 03/28/2012] [Indexed: 05/31/2023]
Abstract
Carbon tetrachloride (CT) is known to inhibit the transformation of perchloroethene (PCE) to ethene by dehalorespiring bacteria, creating a challenge for the bioremediation of environments contaminated with both compounds. We report on the sequential use of sulfate reduction and dehalorespiration as a microbial strategy for the transformation of a mixture of CT (10 μM) and PCE (14 μM). Sulfide production in Desulfovibrio vulgaris cultures led to complete CT disappearance in as little as 12 days. The addition of amorphous ferric oxide decreased the proportion of chloroform (CF) produced from 65% to 30%. CT conversion rates were enhanced more than 13-fold where vitamin B(12) (5 μM) was added. In vitamin B(12)-containing D. vulgaris cultures, no chlorinated products were detected and carbon disulfide was the major product of CT transformation. PCE concentrations were not impacted upon by D. vulgaris activity. The subsequent inoculation of a PCE-respiring enrichment culture resulted in microbial PCE dechlorination to ethene.
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Affiliation(s)
- Joanna C Koenig
- Centre for Marine Bioinnovation, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia
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Microbial removal of atmospheric carbon tetrachloride in bulk aerobic soils. Appl Environ Microbiol 2011; 77:5835-41. [PMID: 21724884 DOI: 10.1128/aem.05341-11] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Atmospheric concentrations of carbon tetrachloride (CCl(4)) were removed by bulk aerobic soils from tropical, subtropical, and boreal environments. Removal was observed in all tested soil types, indicating that the process was widespread. The flux measured in field chamber experiments was 0.24 ± 0.10 nmol CCl(4) (m(2) day)(-1) (average ± standard deviation [SD]; n = 282). Removal of CCl(4) and removal of methane (CH(4)) were compared to explore whether the two processes were linked. Removal of both gases was halted in laboratory samples that were autoclaved, dry heated, or incubated in the presence of mercuric chloride (HgCl(2)). In marl soils, treatment with antibiotics such as tetracycline and streptomycin caused partial inhibition of CCl(4) (50%) and CH(4) (76%) removal, but removal was not affected in soils treated with nystatin or myxothiazol. These data indicated that bacteria contributed to the soil removal of CCl(4) and that microeukaryotes may not have played a significant role. Amendments of methanol, acetate, and succinate to soil samples enhanced CCl(4) removal by 59%, 293%, and 72%, respectively. Additions of a variety of inhibitors and substrates indicated that nitrification, methanogenesis, or biological reduction of nitrate, nitrous oxide, or sulfate (e.g., occurring in possible anoxic microzones) did not play a significant role in the removal of CCl(4). Methyl fluoride inhibited removal of CH(4) but not CCl(4), indicating that CH(4) and CCl(4) removals were not directly linked. Furthermore, CCl(4) removal was not affected in soils amended with copper sulfate or methane, supporting the results with MeF and suggesting that the observed CCl(4) removal was not significantly mediated by methanotrophs.
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Sharma PK, McCarty PL. Isolation and Characterization of a Facultatively Aerobic Bacterium That Reductively Dehalogenates Tetrachloroethene to cis-1,2-Dichloroethene. Appl Environ Microbiol 2010; 62:761-5. [PMID: 16535267 PMCID: PMC1388792 DOI: 10.1128/aem.62.3.761-765.1996] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A rapidly-growing facultatively aerobic bacterium that transforms tetrachloroethene (PCE) via trichloroethene (TCE) to cis-1,2-dichloroethene (cis-1,2-DCE) at high rates in a defined medium was isolated from a contaminated site. Metabolic characterization, cellular fatty acid analysis, and partial sequence analysis of 16S rRNA showed that the new isolate, strain MS-1, has characteristics matching those of the members of the family Enterobacteriaceae. Strain MS-1 can oxidize about 58 substrates including many carbohydrates, short-chain fatty acids, amino acids, purines, and pyrimidines. It can transform up to 1 mM PCE (aqueous) at a rate of about 0.5 (mu)mol of PCE(middot) h(sup-1)(middot)mg (dry weight) of cell(sup-1). PCE transformation occurs following growth on or with the addition of single carbon sources such as glucose, pyruvate, formate, lactate, or acetate or with complex nutrient sources such as yeast extract or a mixture of amino acids. PCE dehalogenation requires the absence of oxygen, nitrate, and high concentrations of fermentable compounds such as glucose. Enterobacter agglomerans biogroup 5 (ATCC 27993), a known facultative bacterium that is closely related to strain MS-1, also reductively dehalogenated PCE to cis-1,2-DCE. To our knowledge, this is the first report on isolation of a facultative bacterium that can reductively transform PCE to cis-1,2-DCE under defined physiological conditions. Also, this is the first report of the ability of E. agglomerans to dehalogenate PCE.
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Munro AW, Girvan HM, McLean KJ. Variations on a (t)heme—novel mechanisms, redox partners and catalytic functions in the cytochrome P450 superfamily. Nat Prod Rep 2007; 24:585-609. [PMID: 17534532 DOI: 10.1039/b604190f] [Citation(s) in RCA: 203] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Andrew W Munro
- Faculty of Life Sciences, Manchester Interdisciplinary Biocentre, University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
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Khare N, Eggleston CM, Lovelace DM, Boese SW. Structural and redox properties of mitochondrial cytochrome c co-sorbed with phosphate on hematite (α-Fe2O3) surfaces. J Colloid Interface Sci 2006; 303:404-14. [PMID: 16945384 DOI: 10.1016/j.jcis.2006.07.070] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 07/11/2006] [Accepted: 07/27/2006] [Indexed: 10/24/2022]
Abstract
The interaction of metalloproteins with oxides has implications not only for bioanalytical systems and biosensors but also in the areas of biomimetic photovoltaic devices, bioremediation, and bacterial metal reduction. Here, we investigate mitochondrial ferricytochrome c (Cyt c) co-sorption with 0.01 and 0.1 M phosphate on hematite (alpha-Fe2O3) surfaces as a function of pH (2-11). Although Cyt c sorption to hematite in the presence of phosphate is consistent with electrostatic attraction, other forces act upon Cyt c as well. The occurrence of multilayer adsorption, and our AFM observations, suggest that Cyt c aggregates as the pH approaches the Cyt c isoelectric point. In solution, methionine coordination of heme Fe occurs only between pH 3 and 7, but in the presence of phosphate this coordination is retained up to pH 10. Electrochemical evidence for the presence of native Cyt c occurs down to pH 3 and up to pH 10 in the absence of phosphate, and this range is extended to pH 2 and 11 in the presence of phosphate. Cyt c that initially adsorbs to a hematite surface may undergo conformation change and coat the surface with unfolded protein such that subsequently adsorbing protein is more likely to retain the native conformational state. AFM provides evidence for rapid sorption kinetics for Cyt c co-sorbed with 0.01 or 0.1 M phosphate. Cyt c co-sorbed with 0.01 M phosphate appears to unfold on the surface of hematite while Cyt c co-sorbed with 0.1 M phosphate possibly retains native conformation due to aggregation.
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Affiliation(s)
- Nidhi Khare
- Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA
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Sims JL, Suflita JM, Russell HH. Reductive dehalogenation: A subsurface bioremediation process. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/rem.3440010109] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Simonneaux G, Le Maux P. Carbene Complexes of Heme Proteins and Iron Porphyrin Models. TOP ORGANOMETAL CHEM 2006. [DOI: 10.1007/3418_006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
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Li YP, Cao HB, Zhang Y. Electrochemical dechlorination of chloroacetic acids (CAAs) using hemoglobin-loaded carbon nanotube electrode. CHEMOSPHERE 2006; 63:359-64. [PMID: 16185744 DOI: 10.1016/j.chemosphere.2005.07.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Revised: 06/28/2005] [Accepted: 07/10/2005] [Indexed: 05/04/2023]
Abstract
Hemoglobin (Hb) was immobilized on carbon nanotube (CNT) electrode to catalyze the dechlorination of chloroacetic acids (CAAs), and the electrocatalytic behaviors of the Hb-loaded electrode for the dechlorination of trichloroacetic acid (TCAA) were studied by cyclic voltammetry and constant-potential electrolysis technique. An Hb-loaded packed-bed flow reactor was also constructed for bioelectrocatalytic dechloriantion of CAAs from drinking water. The results showed that the reduced heme of Hb immobilized on CNT electrode was easily regenerated, and Hb exhibited a stable and high activity for reductive dechlorination of CAAs with significant lowering of overpotential. TCAA could be reduced at -0.450 V (vs. saturated calomel electrode (SCE)) with catalysis of Hb-loaded electrode and its dechlorination was stepwise, following the pathway of TCAA-->dichloroacetic acid (DCAA)-->monochloroacetic acid (MCAA)-->acetic acid. It was also found that all CAAs, e.g., TCAA, DCAA and MCAA, could be dechlorinated completely at -0.450 V. The removal of 30.0 mM TCAA and DCAA is ca. 40% and 31%, respectively, with electrolysis for 100 min at -0.600 V (vs. SCE) using the Hb-loaded packed-bed flow reactor. The dechlorination activities of CAAs follow the decreasing order: TCAA>DCAA>MCAA, and the average current efficiency is over 90%.
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Affiliation(s)
- Yu-Ping Li
- Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, P.O. Box 353, Beijing 100080, China
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20
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Egli C, Stromeyer S, Cook AM, Leisinger T. Transformation of tetra- and trichloromethane to CO2by anaerobic bacteria is a non-enzymic process. FEMS Microbiol Lett 2006. [DOI: 10.1111/j.1574-6968.1990.tb04150.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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21
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Koe GS, Vilker VL. Effect of oxygen on the dehalogenation of 1,2-Dibromo-3-chloropropane by cytochrome P450cam (CYP101). Biotechnol Prog 2006; 21:1119-27. [PMID: 16080691 DOI: 10.1021/bp0500213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytochromes P450 are known to exhibit diverse catalytic functions against a large number of hydrocarbon substrates. The determinants of specific activity(ies) that operate on specific substrates have not been widely explored. Earlier, we showed that dehalogenation of 1,2-dibromo-3-chloropropane (DBCP) by P450cam (CYP101) monooxygenase exhibits oxygen- and substrate-dependent product distributions and reaction rates (1). Bromochloroacetone was the major conversion product when incubation media were saturated with oxygen, whereas allyl chloride was the sole product accounting for virtually all of the DBCP converted in the absence of oxygen. In an effort to develop a quantitative understanding of the effect of oxygen on product distribution and reaction rate, we have identified first generation products and measured reaction rates at four oxygen levels ranging from 0.01% to 100% saturation. In addition to bromochloroacetone and allyl chloride, a number of bromochloropropene isomers were identified in the presence of oxygen and are thought to be formed by an elimination mechanism. These products accounted for greater than 97 mol % of the reacted DBCP, which was run to high conversion (60-100 mol % DBCP converted). These measurements suggest that P450cam acts on the DBCP substrate through hydroxylation to produce 1-bromo-3-chloroacetone, through reduction to produce allyl chloride, and through elimination to produce bromochloropropene, with oxygen concentration determining the extent of each activity. A global data fitting kinetic model that describes the time-varying concentrations of substrate and products was developed to quantify the controlling level of oxygen on these multiple activities. The parameters of the model were compared with independent measurements and data from the literature.
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Affiliation(s)
- Gary S Koe
- Department of Chemical Engineering, UCLA, Los Angeles, CA, USA
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22
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Obare SO, Ito T, Meyer GJ. Controlling reduction potentials of semiconductor-supported molecular catalysts for environmental remediation of organohalide pollutants. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2005; 39:6266-72. [PMID: 16173591 DOI: 10.1021/es048058r] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The spectroscopic and redox properties of iron(lll) protoporphyrin chloride (hemin) and cobalt(lll) meso-tetra-(4-carboxyphenyl) porphyrin chloride (CoTCP) were quantified in fluid solution and when anchored to mesoporous nanocrystalline TiO2 thin films. Surface binding was well-described by the Langmuir adsorption isotherm model from which adduct formation constants of 10(5) M(-1) and limiting surface coverages of 10(-8) mol/cm2 were abstracted. In acetonitrile and dimethyl sulfoxide electrolytes, TiO2 binding was found to induce a substantial negative shift in the M(III/II) formal reduction potentials. In DMSO electrolyte, the Co(III/II) and Fe(III/II) potentials were -559 and -727 mV versus ferrocenium/ferrocene (Fc+/Fc) and shifted to -782 and -1063 mV, respectively, after surface binding. The Bronsted acidity of the TiO2 surface was found to correlate with the measured reduction potentials. For TiO2 pretreated with aqueous solutions from pH 4-9, the Co(III/II) potential showed a -66 mV/pH unit change, while the Fe(llI/II) potential of hemin changed by -40 mV/pH from pH 1 to 14. Spectroelectrochemical data gave isosbestic, reversible spectral changes in the visible region assigned to M(III/II) redox chemistry with lambda(iso) = 410, 460, 530, 545, 568, and 593 nm for CoTCP/TiO2 and lambda(iso) = 408, 441, 500, 576, and 643 nm for hemin/TiO2. In aqueous solution, the CoTCP reduction potentials were also found to be pH dependent upon surface binding, with CoTCP = -583 mV and CoTCP/TiO2 = -685 mV versus Fc+/Fc at pH 6. For CoTCP/TiO2, the aqueous pH dependence of the potentials was -52 mV/pH. The rate constant for heme/TiO2 reduction of CCl4 increased from 3.9 +/- 0.7 x 10(-4) to 2.0 +/- 0.1 x 10(-3) s(-1) when the pH was raised from 4 to 8.
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Affiliation(s)
- Sherine O Obare
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Chapter 10 Non-affinity sensing technology: the exploitation of biocatalytic events for environmental analysis. BIOSENSORS AND MODERN BIOSPECIFIC ANALYTICAL TECHNIQUES 2005. [DOI: 10.1016/s0166-526x(05)44010-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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24
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Lucchese B, Humphreys KJ, Lee DH, Incarvito CD, Sommer RD, Rheingold AL, Karlin KD. Mono-, Bi-, and Trinuclear CuII-Cl Containing Products Based on the Tris(2-pyridylmethyl)amine Chelate Derived from Copper(I) Complex Dechlorination Reactions of Chloroform. Inorg Chem 2004; 43:5987-98. [PMID: 15360248 DOI: 10.1021/ic0497477] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ligand TMPA (tris(2-pyridylmethyl)amine) and its copper complexes have played a prominent role in recent (bio)inorganic chemistry studies; the copper(I) complex [CuI(TMPA)(CH3CN)]+ possesses an extensive dioxygen reactivity, and it is also known to effect the reductive dechlorination of substrates such as dichloromethane and benzyl and allyl chlorides. In this report, we describe a set of new analogues of TMPA, ligand 6TMPAOH, binucleating Iso-DO, and trinucleating SYMM. Copper(I) complexes with these ligands and a previously described binucleating ligand DO react with chloroform, resulting in reductive dechlorination and production of [CuIIx(L)Clx]x+ (x = 1, 2, or 3). X-ray crystal structures of [CuII(6TMPAOH)Cl]PF6, [CuII2(Iso-DO)Cl2](PF6)2, [CuII2(DO)Cl2](PF6)2, and [Cu3(SYMM)Cl3](PF6)3 are presented, and the compounds are also characterized by UV-vis and EPR spectroscopies as well as cyclic voltammetry. The steric influence of a pyridyl 6-substituent (in the complexes with 6TMPAOH, Iso-DO, and SYMM) on the solid state and solution structures and redox potentials are compared and contrasted to those chlorocopper(II) complexes with a pyridyl 5'-substituent (in [CuII2(DO)Cl2](PF6)2 and in [CuII(TMPA)Cl]+). Some insights into the reductive dechlorination process have been obtained by using 2H NMR spectroscopy in following the reaction of [Cu2(Iso-DO)(CH3CN)2](PF6)2 with CDCl3, in the presence or absence of a radical trap, 2,4-di-tert-butylphenol.
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Affiliation(s)
- Baldo Lucchese
- Department of Chemistry, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
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Bistolas N, Christenson A, Ruzgas T, Jung C, Scheller FW, Wollenberger U. Spectroelectrochemistry of cytochrome P450cam. Biochem Biophys Res Commun 2004; 314:810-6. [PMID: 14741708 DOI: 10.1016/j.bbrc.2003.12.159] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The spectroelectrochemistry of camphor-bound cytochrome P450cam (P450cam) using gold electrodes is described. The electrodes were modified with either 4,4(')-dithiodipyridin or sodium dithionite. Electrolysis of P450cam was carried out when the enzyme was in solution, while at the same time UV-visible absorption spectra were recorded. Reversible oxidation and reduction could be observed with both 4,4(')-dithiodipyridin and dithionite modified electrodes. A formal potential (E(0')) of -373mV vs Ag/AgCl 1M KCl was determined. The spectra of P450cam complexed with either carbon monoxide or metyrapone, both being inhibitors of P450 catalysis, clearly indicated that the protein retained its native state in the electrochemical cell during electrolysis.
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Affiliation(s)
- Nikitas Bistolas
- Department of Analytical Biochemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany
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26
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Lewis TA, Paszczynski A, Gordon-Wylie SW, Jeedigunta S, Lee CH, Crawford RL. Carbon tetrachloride dechlorination by the bacterial transition metal chelator pyridine-2,6-bis(thiocarboxylic acid). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2001; 35:552-559. [PMID: 11351728 DOI: 10.1021/es001419s] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A reaction pathway is proposed to explain the formation of end products during defined chemical reactions between carbon tetrachloride (CCl4) and either metal complexes of pyridine-2,6-bis(thiocarboxylic acid) (PDTC) or pure cultures of Pseudomonas stutzeri KC. The pathway includes one-electron reduction of CCl4 by the Cu(II):PDTC complex, condensation of trichloromethyl and thiyl radicals, and hydrolysis of a labile thioester intermediate. Products detected were carbon dioxide, chloride, carbonyl sulfide, carbon disulfide, and dipicolinic acid. Spin-trapping and electrospray MS/MS experiments gave evidence of trichloromethyl and thiyl radicals generated by reaction of CCl4 with PDTC and copper. Experiments testing the effects of transition metals showed that dechlorination by PDTC requires copper and is inhibited by cobalt but not by iron or nickel. PDTC was shown to react stoichiometrically rather than catalytically without added reducing equivalents. With added reductants, an increased turnover was seen along with increased chloroform production.
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Affiliation(s)
- T A Lewis
- Department of Microbiology and Molecular Genetics and Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA
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27
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Walsh ME, Kyritsis P, Eady NA, Hill HA, Wong LL. Catalytic reductive dehalogenation of hexachloroethane by molecular variants of cytochrome P450cam (CYP101). EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5815-20. [PMID: 10971594 DOI: 10.1046/j.1432-1327.2000.01666.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
CYP101 (cytochrome P450cam) catalyses the oxidation of camphor but has also been shown to catalyse the reductive dehalogenation of hexachloroethane and pentachloroethane. This reaction has potential applications in the biodegradation of these environmental contaminants. The hexachloroethane dehalogenation activity of CYP101 has been investigated by mutagenesis. The effects of active-site polarity and volume were probed by combinations of active-site mutations. Increasing the active-site hydrophobicity by the Y96A and Y96F mutations strengthened hexachloroethane binding but decreased the rate of reaction. Increasing the polarity with the F87Y mutation drastically weakened hexachloroethane binding but did not affect the rate of reaction. The Y96H mutation had little effect at pH 7.4, but weakened hexachloroethane binding while increasing the rate of dehalogenation by up to 40% at pH 6.5, suggesting that the imidazole side-chain was partially protonated at pH 6.5 but not at pH 7.4. Substitutions by bulkier side-chains at F87, T101 and V247 weakened hexachloroethane binding but increased the dehalogenation rate. The effect of the individual mutations was additive in multiple mutants, and the most active mutant for hexachloroethane reductive dehalogenation at pH 7.4 was F87W-V247L (80 min-1 or 2.5 x the activity of the wild-type). The results suggested that the CYP101 active site shows good match with hexachloroethane, the Y96 side-chain plays an important role in both hexachloroethane binding and dehalogenation, and hexachloroethane binding and dehalogenation places conflicting demands on active-site polarity and compromises were necessary to achieve reasonable values for both.
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Affiliation(s)
- M E Walsh
- Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, UK
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Prakash, Gupta SK. Effect of Carbon Source on PCE Dehalogenation. JOURNAL OF ENVIRONMENTAL ENGINEERING 2000; 126:622-628. [DOI: 10.1061/(asce)0733-9372(2000)126:7(622)] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2023]
Affiliation(s)
- Prakash
- Sr. Lect., P.E.S. Coll. of Engrg., Mandya 571401, Karnataka State, India
- Prof., Ctr. for Envir. Sci. and Engrg., Indian Inst. of Technol., Bombay, Powai, Mumbai 400 076, India
| | - S. K. Gupta
- Sr. Lect., P.E.S. Coll. of Engrg., Mandya 571401, Karnataka State, India
- Prof., Ctr. for Envir. Sci. and Engrg., Indian Inst. of Technol., Bombay, Powai, Mumbai 400 076, India
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30
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Wirtz M, Klucik J, Rivera M. Ferredoxin-Mediated Electrocatalytic Dehalogenation of Haloalkanes by Cytochrome P450cam. J Am Chem Soc 2000. [DOI: 10.1021/ja993648o] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Marc Wirtz
- Contribution from the Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078-3071
| | - Josef Klucik
- Contribution from the Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078-3071
| | - Mario Rivera
- Contribution from the Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078-3071
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31
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Singh BK, Kuhad RC, Singh A, Lal R, Tripathi KK. Biochemical and molecular basis of pesticide degradation by microorganisms. Crit Rev Biotechnol 1999; 19:197-225. [PMID: 10526405 DOI: 10.1080/0738-859991229242] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- B K Singh
- Department of Microbiology, University of Delhi, India
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Kawahara N, Ikatsu H, Kawata H, Miyoshi SI, Tomochika KI, Sinoda S. Purification and characterization of 2-ethoxyphenol-induced cytochrome P450 fromCorynebacteriumsp. strain EP1. Can J Microbiol 1999. [DOI: 10.1139/w99-082] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A soluble cytochrome P450 (P450EP1A) induced by 2-ethoxyphenol was purified to apparent homogeneity from Corynebacterium sp. strain EP1. The P450EP1Ashowed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular weight of about 45 kDa. The CO-reduced difference spectra of P450EP1Ahad a Soret maximum at 447.6 nm. The substrate difference spectra with 2-ethoxyphenol showed an absorption maximum at 394.0 nm. The purified P450EP1Adegraded 2-ethoxyphenol in an assay system composed of spinach ferredoxin-NADP+oxidoreductase and NADPH. The reaction activity decreased to 1.4% of its original activity by addition of CO. The existence of catechol in the reaction mixture was confirmed after the metabolic reaction, indicating that P450EP1Acatalyzes O-dealkylation of 2-ethoxyphenol. In addition to 2-ethoxyphenol, the P450EP1Ametabolized 2-methoxyphenol, 1,1,1-trichloroethane, carbon tetrachloride, benzene, and toluene.Key words: cytochrome P450, Corynebacterium sp., 2-ethoxyphenol, enzyme purification, biodegradation.
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33
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Lee CH, Lewis TA, Paszczynski A, Crawford RL. Identification of an extracellular agent [correction of catalyst] of carbon tetrachloride dehalogenation from Pseudomonas stutzeri strain KC as pyridine-2, 6-bis(thiocarboxylate). Biochem Biophys Res Commun 1999; 261:562-6. [PMID: 10441466 DOI: 10.1006/bbrc.1999.1077] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pseudomonas stutzeri strain KC was originally characterized as having, under iron-limiting conditions, novel carbon tetrachloride (CCl(4)) dehalogenation activity, specifically, a net conversion of CCl(4) to CO(2). The exact pathway and reaction mechanisms are unknown, but chloroform is not an intermediate and thiophosgene and phosgene have been identified as intermediates in trapping experiments. Previous work by others using cell-free preparations has shown that cell-free culture supernatants that have been passed through a low-molecular-weight cutoff membrane can confer rapid CCl(4) transformation ability upon cultures of bacteria which otherwise show little or no reactivity toward CCl(4). We used a cell-free assay system to monitor the complete purification of compounds showing CCl(4) degradation activity elaborated by iron-limited cultures of strain KC. Electrospray tandem mass spectroscopy, NMR spectroscopy, and comparisons with synthetic material have identified pyridine-2,6-bis(thiocarboxylate) as a metabolite of strain KC which has CCl(4) transformation activity in the presence of chemical reductants, e.g., titanium[III] citrate or dithiothreitiol, or actively growing bacterial cultures.
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Affiliation(s)
- C H Lee
- Department of Microbiology, Molecular Biology, and Biochemistry, University of Idaho, Moscow, Idaho, 83844-1052, USA
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34
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Grayson DA, Vilker VL. Kinetic characterization of chiral biocatalysis of cycloarenes by the camphor 5-monooxygenase enzyme system. ACTA ACUST UNITED AC 1999. [DOI: 10.1016/s1381-1177(99)00003-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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35
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Schneider M, Quistad GB, Casida JE. Glutathione activation of chloropicrin in the Salmonella mutagenicity test. Mutat Res 1999; 439:233-8. [PMID: 10023070 DOI: 10.1016/s1383-5718(98)00198-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Chloropicrin (CCl3NO2) is a major soil fumigant for control of fungi, insects and nematodes and may by formed by chlorination of drinking water. It is also a strong lacrimator and induces sister chromatid exchanges in cultured human lymphocytes. Mutagenicity assays of CCl3NO2 in Salmonella typhimurium TA100 establish that it is toxic but not mutagenic at 500 nmol/plate but becomes mutagenic but not toxic on addition of S9 (previous work) or 1-2 molar equivalents of glutathione (GSH) (this study). The preincubation assay is superior to the plate incorporation test giving 2-4-fold higher revertants/nmol. Using the preincubation assay with GSH at 5 mM (a biomimetic level) in the top agar gives linear dose-response relationships for CCl3NO2 and its dechlorination products CHCl2NO2 and CH2ClNO2 with 0.56, 0.56 and 1.8 revertants/nmol, respectively. The mutagenicity values for CHCl2NO2 and CH2ClNO2 are the same in the presence and the absence of GSH, which only improves the linearity at high levels by reducing toxicity to the bacteria. GSH activation of CCl3NO2 mutagenicity may be due to reductive dechlorination of the trichloro compound to the more active CHCl2NO2 and CH2ClNO2. Alternatively, the mutagenicity may result from an intermediate GSH conjugate such as GSCCl2NO2 or GSCHClNO2. In comparison, the mutagenicity of CH2Br2 and CH2I2 is affected little if any by addition of GSH and these dihalomethanes are much less active than the halonitromethane series. It therefore appears that CCl3NO2 is not mutagenic in the absence of activation and that the dechlorinated metabolites CHCl2NO2 and CH2ClNO2 are moderately potent bacterial mutagens, consistent with the possible genotoxicity of CCl3NO2 in mammals.
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Affiliation(s)
- M Schneider
- Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112, USA
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36
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Abstract
Biocatalysis is important in both natural and engineered environments. The major global reactions in the biospheric cycling of carbon, nitrogen, and other elements are catalyzed by microorganisms. The global carbon cycle includes millions of organic compounds that are made by plants, microorganisms, and organic chemists. Most of those compounds are transformed by microbial enzymes. Degradative metabolism is known as catabolism and yields principally carbon dioxide, methane, or biomass. Microbial catabolic enzymes are a great resource for biotechnology. They are the building blocks for engineering novel metabolic pathways and evolving improved enzymes in the laboratory. Two multicomponent bacterial oxygeneases, cytochrome P450cam and toluene dioxygenase, catalyze the dechlorination of polyhalogenated C2 compounds. Seven genes encoding those functional enzyme complexes were coexpressed in a Pseudomonas and shown to metabolize pentachloreothane to nonhalogenated organic acids that were metabolized further to carbon dioxide. In another example, the enzyme catalyzing the dechlorination of the herbicide atrazine was subjected to iterative DNA shuffling to produce mutations. By using a plate screening assay, mutated atrazine chlorohydrolase that catalyzed a more rapid dechlorination of atrazine was obtained. The mutant genes were sequences and found to encode up to 11 amino acid changes. Atrazine chlorohydrolase is currently being used in a model municipal water treatment system to test the feasibility of using enzymes for atrazine decontamination. These data suggest that the natural diversity of bacterial catabolic enzymes provides the starting point for improved biocatalytic systems that meet the needs of commercial applications.
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Affiliation(s)
- L P Wackett
- Department of Biochemistry, University of Minnesota, St. Paul 55108, USA
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37
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Yanagita K, Sagami I, Daff S, Shimizu T. Marked enhancement in the reductive dehalogenation of hexachloroethane by a Thr319Ala mutation of cytochrome P450 1A2. Biochem Biophys Res Commun 1998; 249:678-82. [PMID: 9731196 DOI: 10.1006/bbrc.1998.9084] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutation of the conserved Thr319 residue to Ala of cytochrome P4501A2 (CYP1A2) increased the value of Vmax 9-fold for reductive dehalogenation of hexachloroethane in the reconstituted system under anaerobic conditions. The Thr319Ala mutation also increased the elimination over substitution product ratio by 5-fold. The addition of aliphatic alcohols increased by 22-fold the activity obtained with the wild type and varied the elimination over substitution product ratio. Increasing pH increased the ratio of elimination over substitution by primarily affecting the rate of elimination.
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Affiliation(s)
- K Yanagita
- Institute for Chemical Reaction Science, Tohoku University, Sendai, Japan
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38
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Castro CE. Environmental dehalogenation: chemistry and mechanism. REVIEWS OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 1998; 155:1-67. [PMID: 9577227 DOI: 10.1007/978-1-4612-1684-1_1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The halogen cycle is one of the great chemical cycles on earth. Haloorganics are both synthesized and destroyed by the chemistry that controls their flux and form. The synthetic leg of the cycle is both biotic and abiotic in nature. The biotic synthesis results primarily from the biochemical activity of marine algae and kelp, although these are by no means the only sources. The abiotic process is vested in large part in volcanic eruption and emission of gases synthesized as a thermal consequence of venting the earth's core.
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Affiliation(s)
- C E Castro
- CEC Consulting, Laguna Beach, CA 92651, USA
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39
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The oxidation of cyclic alcohols from an aqueous solution by manganese porphyrins embedded in a polydimethylsiloxane membrane. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1381-1169(97)00129-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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40
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Nassar AEF, Zhang Z, Hu N, Rusling JF, Kumosinski TF. Proton-Coupled Electron Transfer from Electrodes to Myoglobin in Ordered Biomembrane-like Films. J Phys Chem B 1997. [DOI: 10.1021/jp962896t] [Citation(s) in RCA: 208] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alaa-Eldin F. Nassar
- Department of Chemistry, Box U-60, University of Connecticut, Storrs, Connecticut 06269-4060
| | - Zhe Zhang
- Department of Chemistry, Box U-60, University of Connecticut, Storrs, Connecticut 06269-4060
| | - Naifei Hu
- Department of Chemistry, Box U-60, University of Connecticut, Storrs, Connecticut 06269-4060
| | - James F. Rusling
- Department of Chemistry, Box U-60, University of Connecticut, Storrs, Connecticut 06269-4060
| | - Thomas F. Kumosinski
- Eastern Regional Research Center, U.S. Department of Agriculture, Philadelphia, Pennsylvania 19118
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Abstract
Microorganisms are able to degrade a large variety of compounds, including pesticides under laboratory conditions. However, methods have yet to be developed to decontaminate the environment from residues of pesticides. Pesticidal degradative genes in microbes have been found to be located on plasmids, transposons, and/or on chromosomes. Recent studies have provided clues to the evolution of degradative pathways and the organization of catabolic genes, thus making it much easier to develop genetically engineered microbes for the purpose of decontamination. Genetic manipulation offers a way of engineering microorganisms to deal with a pollutant, including pesticides that may be present in the contaminated sites. The simplest approach is to extend the degradative capabilities of existing metabolic pathways within an organism either by introducing additional enzymes from other organisms or by modifying the specificity of the catabolic genes already present. Continuous efforts are required in this direction, and at present several bacteria capable of degrading pesticides have been isolated from the natural environment. Catabolic genes responsible for the degradation of several xenobiotics, including pesticides, have been identified, isolated, and cloned into various other organisms such as Streptomyces, algae, fungi, etc. In addition, recombinant DNA studies have made it possible to develop DNA probes that are being used to identify microbes from diverse environmental communities with an unique ability to degrade pesticides.
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Affiliation(s)
- S Kumar
- Agrochemicals and Pest Management, USIC (old) University of Delhi
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Ni S, Fredrickson JK, Xun L. Purification and characterization of a novel 3-chlorobenzoate-reductive dehalogenase from the cytoplasmic membrane of Desulfomonile tiedjei DCB-1. J Bacteriol 1995; 177:5135-9. [PMID: 7665493 PMCID: PMC177294 DOI: 10.1128/jb.177.17.5135-5139.1995] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Although reductive dehalogenation by anaerobic microorganisms offers great potential for the degradation of halocarbons, little is known about the biochemical mechanisms involved. It has previously been demonstrated that the dehalogenase activity involved in 3-chlorobenzoate dehalogenation by Desulfomonile tiedjei DCB-1 is present in the membrane fraction of the cell extracts. We report herein the purification of a 3-chlorobenzoate-reductive dehalogenase from the cytoplasmic membrane of D. tiedjei DCB-1. The dehalogenase activity was monitored by the conversion of 3-chlorobenzoate to benzoate with reduced methyl viologen as a reducing agent. The membrane fraction of the cell extracts was obtained by ultracentrifugation, and the membrane proteins were solubilized with either the detergent CHAPS (3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate) or Triton X-100 in the presence of glycerol. The solubilized dehalogenase was purified by ammonium sulfate fractionation and a combination of anion exchange, hydroxyapatite, and hydrophobic interaction chromatographies. This procedure yielded about 7% of the total dehalogenase activity with a 120-fold increase in specific activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the purified dehalogenase consisted of two subunits with molecular weights of 64,000 and 37,000. The enzyme converted 3-chlorobenzoate to benzoate at its highest specific activity in 10 mM potassium phosphate buffer (pH 7.2) at 38 degrees C. The enzyme was yellow and probably a heme protein. The enzyme had an adsorbance peak at 408 nm. The dithionite-reduced enzyme displayed absorbance peaks at 416, 522, and 550 nm. The dithionite-reduced enzyme was able to complex with carbon monoxide. The nature of the heme chromophore is currently unknown.
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Affiliation(s)
- S Ni
- Environmental Microbiology Group, Pacific Northwest Laboratory, Richland, Washington 99352, USA
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Liu SM, Jones WJ. Biotransformation of dichloroaromatic compounds in nonadapted and adapted freshwater sediment slurries. Appl Microbiol Biotechnol 1995; 43:725-32. [PMID: 7546610 DOI: 10.1007/bf00164780] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Nonadapted freshwater sediment slurries and sediment slurries adapted to dechlorinate 2,3-dichloropyridine (2,3-Cl2Pyd), 2,3-dichloroaniline (2,3-Cl2Anl), 2,3-dichlorophenol (2,3-Cl2PhOH), 3,5-dichloropyridine (3,5-Cl2Pyd), 3,5-dichloroaniline (3,5-Cl2Anl) and 3,5-dichlorophenol (3,5-Cl2PhOH) were studied to determine the rate, range and extent of biotransformation of structurally related compounds under anaerobic conditions. 2,3-dichloroanisole (2,3-Cl2Ans) and 3,5-dichloroanisole (3,5-Cl2Ans) were initially demethylated, producing 2,3-Cl2PhOH and 3,5-Cl2PhOH as intermediate transformation products. All other dichloroaromatic compounds examined were initially dechlorinated. The rates of dechlorination of 2,3-Cl2PhOH, 2,3-Cl2Anl, and 2,3-Cl2Pyd were significantly lower (5-15 times) in nonadapted sediment slurries compared to sediment slurries adapted to 2,3-Cl2Anl or 2,3-Cl2Pyd. In 2,3-Cl2PhOH adapted sediment, the rate of dechlorination of 2,3-Cl2PhOH was 15 times greater than in nonadapted sediment; however, the rates of dechlorination of 2,3-Cl2Anl and 2,3-Cl2Pyd were similar for 2,3-Cl2PhOH-adapted and nonadapted sediment slurries. In adapted and nonadapted sediment slurries, 2,3-Cl2PhOH, 2,3-Cl2Anl, and 2,3-Cl2Pyd were preferentially dechlorinated at the ortho, meta, and meta positions, respectively. Additionally, 2,3-Cl2Pyd adapted sediment slurries dechlorinated 2,3-Cl2PhOH and 2,3-Cl2Pyd at both ortho and meta positions. Rates of dechlorination of 3,5-Cl2PhOH, 3,5-Cl2Anl, and 3,5-Cl2Pyd were lower (2-4 times) in nonadapted sediment slurries compared to sediment slurries adapted to 3,5-Cl2Anl or 3,5-Cl2Pyd. In 3,5-Cl2PhOH adapted sediment, the rate of dechlorination of 3,5-Cl2PhOH was approximately 10 times greater than in nonadapted sediment.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S M Liu
- University of Georgia, Athens 30602, USA
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Uotila JS, Kitunen VH, Coote T, Saastamoinen T, Salkinoja-Salonen M, Apajalahti JH. Metabolism of halohydroquinones in Rhodococcus chlorophenolicus PCP-1. Biodegradation 1995; 6:119-26. [PMID: 7772938 DOI: 10.1007/bf00695342] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The actinomycete Rhodococcus chlorophenolicus PCP-1 metabolizes pentachlorophenol into ultimate inorganic end products via tetrachloro-p-hydroquinone. This intermediate was further dehalogenated in the cytoplasm requiring reductant in the cell free system. Tetrafluoro-p-hydroquinone and tetrabromo-p-hydroquinone were also dehalogenated. Chlorophenol analogs, thiol blocking agents and molecular oxygen inhibited the activity. The dehalogenating reactions led to 1,2,4-trihydroxybenzene, which was further metabolized into maleic acid.
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Affiliation(s)
- J S Uotila
- Department of Applied Chemistry and Microbiology, University of Helsinki, Finland
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Chiu PC, Reinhard M. Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution. ENVIRONMENTAL SCIENCE & TECHNOLOGY 1995; 29:595-603. [PMID: 22200267 DOI: 10.1021/es00003a006] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
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Fetzner S, Lingens F. Bacterial dehalogenases: biochemistry, genetics, and biotechnological applications. Microbiol Rev 1994; 58:641-85. [PMID: 7854251 PMCID: PMC372986 DOI: 10.1128/mr.58.4.641-685.1994] [Citation(s) in RCA: 148] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This review is a survey of bacterial dehalogenases that catalyze the cleavage of halogen substituents from haloaromatics, haloalkanes, haloalcohols, and haloalkanoic acids. Concerning the enzymatic cleavage of the carbon-halogen bond, seven mechanisms of dehalogenation are known, namely, reductive, oxygenolytic, hydrolytic, and thiolytic dehalogenation; intramolecular nucleophilic displacement; dehydrohalogenation; and hydration. Spontaneous dehalogenation reactions may occur as a result of chemical decomposition of unstable primary products of an unassociated enzyme reaction, and fortuitous dehalogenation can result from the action of broad-specificity enzymes converting halogenated analogs of their natural substrate. Reductive dehalogenation either is catalyzed by a specific dehalogenase or may be mediated by free or enzyme-bound transition metal cofactors (porphyrins, corrins). Desulfomonile tiedjei DCB-1 couples energy conservation to a reductive dechlorination reaction. The biochemistry and genetics of oxygenolytic and hydrolytic haloaromatic dehalogenases are discussed. Concerning the haloalkanes, oxygenases, glutathione S-transferases, halidohydrolases, and dehydrohalogenases are involved in the dehalogenation of different haloalkane compounds. The epoxide-forming halohydrin hydrogen halide lyases form a distinct class of dehalogenases. The dehalogenation of alpha-halosubstituted alkanoic acids is catalyzed by halidohydrolases, which, according to their substrate and inhibitor specificity and mode of product formation, are placed into distinct mechanistic groups. beta-Halosubstituted alkanoic acids are dehalogenated by halidohydrolases acting on the coenzyme A ester of the beta-haloalkanoic acid. Microbial systems offer a versatile potential for biotechnological applications. Because of their enantiomer selectivity, some dehalogenases are used as industrial biocatalysts for the synthesis of chiral compounds. The application of dehalogenases or bacterial strains in environmental protection technologies is discussed in detail.
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Affiliation(s)
- S Fetzner
- Institut für Mikrobiologie der Universität Hohenheim, Stuttgart, Germany
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Hur HG, Sadowsky MJ, Wackett LP. Metabolism of chlorofluorocarbons and polybrominated compounds by Pseudomonas putida G786(pHG-2) via an engineered metabolic pathway. Appl Environ Microbiol 1994; 60:4148-54. [PMID: 7993096 PMCID: PMC201949 DOI: 10.1128/aem.60.11.4148-4154.1994] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The recombinant bacterium Pseudomonas putida G786(pHG-2) metabolizes pentachloroethane to glyoxylate and carbon dioxide, using cytochrome P-450CAM and toluene dioxygenase to catalyze consecutive reductive and oxidative dehalogenation reactions (L.P. Wackett, M.J. Sadowsky, L.N. Newman, H.-G. Hur, and S. Li, Nature [London] 368:627-629, 1994). The present study investigated metabolism of brominated and chlorofluorocarbon compounds by the recombinant strain. Under anaerobic conditions, P. putida G786(pHG-2) reduced 1,1,2,2-tetrabromoethane, 1,2-dibromo-1,2-dichloroethane, and 1,1,1,2-tetrachloro-2,2-difluoroethane to products bearing fewer halogen substituents. Under aerobic conditions, P. putida G786(pHG-2) oxidized cis- and trans-1,2-dibromoethenes, 1,1-dichloro-2,2-difluoroethene, and 1,2-dichloro-1-fluoroethene. Several compounds were metabolized by sequential reductive and oxidative reactions via the constructed metabolic pathway. For example, 1,1,2,2-tetrabromoethane was reduced by cytochrome P-450CAM to 1,2-dibromoethenes, which were subsequently oxidized by toluene dioxygenase. The same pathway metabolized 1,1,1,2-tetrachloro-2,2-difluoroethane to oxalic acid as one of the final products. The results obtained in this study indicate that P. putida G786(pHG-2) metabolizes polyfluorinated, chlorinated, and brominated compounds and further demonstrates the value of using a knowledge of catabolic enzymes and recombinant DNA technology to construct useful metabolic pathways.
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Affiliation(s)
- H G Hur
- Department of Soil Science, University of Minnesota, St. Paul 55108
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Holliger C, Schraa G. Physiological meaning and potential for application of reductive dechlorination by anaerobic bacteria. FEMS Microbiol Rev 1994; 15:297-305. [PMID: 7946473 DOI: 10.1111/j.1574-6976.1994.tb00141.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The physiological meaning of reductive dechlorination reactions catalyzed by anaerobic bacteria can be explained as a co-metabolic activity or as a novel type of respiration. Co-metabolic activities have been found mainly with alkyl halides. They are non-specific reactions catalyzed by various enzyme systems of facultative as well as obligate anaerobic bacteria. In contrast, the reductive dechlorinations involved in metabolic respiration processes are very specific reactions. Only a limited number of alkyl and aryl chlorinated compounds is presently known to function as a terminal electron acceptor in a few, recently isolated bacteria. Metabolic dechlorination rates are in general several orders of magnitude higher than co-metabolic ones. Both reaction types are suitable for the anaerobic treatment of waste streams.
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Affiliation(s)
- C Holliger
- Limnological Research Center, EAWAG, Kastanienbaum, Switzerland
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50
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Petrovskis EA, Vogel TM, Adriaens P. Effects of electron acceptors and donors on transformation of tetrachloromethane by Shewanella putrefaciens MR-1. FEMS Microbiol Lett 1994; 121:357-63. [PMID: 7926693 DOI: 10.1111/j.1574-6968.1994.tb07126.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Transformation of chlorinated aliphatic compounds was examined in Shewanella putrefaciens strain MR-1, an obligately respiring facultative anaerobe. Under anaerobic conditions, MR-1 has been shown to transform tetrachloromethane to trichloromethane (24%), CO2 (7%), cell-bound material (50%) and unidentified nonvolatile products (4%). The highest rate and extent of transformation were observed with MR-1 cells grown under iron(III)-respiring conditions. Lactate, formate and hydrogen were the most effective electron donors. Tetrachloromethane was not degraded in the presence of oxygen. Transformation of other chlorinated methanes and ethenes was not observed.
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Affiliation(s)
- E A Petrovskis
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor 48109-2125
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