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Besalú-Sala P, Magallón C, Costas M, Company A, Luis JM. Mechanistic Insights into the ortho-Defluorination-Hydroxylation of 2-Halophenolates Promoted by a Bis(μ-oxo)dicopper(III) Complex. Inorg Chem 2020; 59:17018-17027. [PMID: 33156988 DOI: 10.1021/acs.inorgchem.0c02246] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
C-F bonds are one of the most inert functionalities. Nevertheless, some [Cu2O2]2+ species are able to defluorinate-hydroxylate ortho-fluorophenolates in a chemoselective manner over other ortho-halophenolates. Albeit it is known that such reactivity is promoted by an electrophilic attack of a [Cu2O2]2+ core over the arene ring, the crucial details of the mechanism that explain the chemo- and regioselectivity of the reaction remain unknown, and it has not being determined either if CuII2(η2:η2-O2) or CuIII2(μ-O)2 species are responsible for the initial attack on the arene. Herein, we present a combined theoretical and experimental mechanistic study to unravel the origin of the chemoselectivity of the ortho-defluorination-hydroxylation of 2-halophenolates by the [Cu2(O)2(DBED)2]2+ complex (DBED = N,N'-di-tert-butylethylenediamine). Our results show that the equilibria between (side-on)peroxo (P) and bis(μ-oxo) (O) isomers plays a key role in the mechanism, with the latter being the reactive species. Furthermore, on the basis of quantum-mechanical calculations, we were able to rationalize the chemoselective preference of the [Cu2(O)2(DBED)2]2+ catalyst for the C-F activation over C-Cl and C-H activations.
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Affiliation(s)
- Pau Besalú-Sala
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany 69, 17003 Girona, Catalonia, Spain
| | - Carla Magallón
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany 69, 17003 Girona, Catalonia, Spain
| | - Miquel Costas
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany 69, 17003 Girona, Catalonia, Spain
| | - Anna Company
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany 69, 17003 Girona, Catalonia, Spain
| | - Josep M Luis
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany 69, 17003 Girona, Catalonia, Spain
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Abstract
Flavin-dependent enzymes catalyze a wide variety of biological reactions that are important for all types of living organisms. Knowledge gained from studying the chemistry and biological functions of flavins and flavin-dependent enzymes has continuously made significant contributions to the development of the fields of enzymology and metabolism from the 1970s until now. The enzymes have been applied in various applications such as use as biocatalysts in synthetic processes for the chemical and pharmaceutical industries or in the biodetoxification and bioremediation of toxic or unwanted compounds, and as biosensors or biodetection tools for quantifying various agents of interest. Many flavin-dependent enzymes are also prime targets for drug development. Based on their reaction mechanisms, they can be classified into five categories: oxidase, dehydrogenase, monooxygenase, reductase, and redox neutral flavin-dependent enzymes. In this chapter, the general properties of flavin-dependent enzymes and the nature of their chemical reactions are discussed, along with their practical applications.
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Abstract
Fluorochemicals are a widely distributed class of compounds and have been utilized across a wide range of industries for decades. Given the environmental toxicity and adverse health threats of some fluorochemicals, the development of new methods for their decomposition is significant to public health. However, the carbon-fluorine (C-F) bond is among the most chemically robust bonds; consequently, the degradation of fluorinated hydrocarbons is exceptionally difficult. Here, metalloenzymes that catalyze the cleavage of this chemically challenging bond are reviewed. These enzymes include histidine-ligated heme-dependent dehaloperoxidase and tyrosine hydroxylase, thiolate-ligated heme-dependent cytochrome P450, and four nonheme oxygenases, namely, tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, 2-oxoglutarate-dependent hydroxylase, Rieske dioxygenase, and thiol dioxygenase. While much of the literature regarding the aforementioned enzymes highlights their ability to catalyze C-H bond activation and functionalization, in many cases, the C-F bond cleavage has been shown to occur on fluorinated substrates. A copper-dependent laccase-mediated system representing an unnatural radical defluorination approach is also described. Detailed discussions on the structure-function relationships and catalytic mechanisms provide insights into biocatalytic defluorination, which may inspire drug design considerations and environmental remediation of halogenated contaminants.
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Affiliation(s)
- Yifan Wang
- Department of Chemistry, University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, USA.
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Turaeva N. Simple electronic model of enzymatic reactions. COMPUT THEOR CHEM 2020. [DOI: 10.1016/j.comptc.2020.112827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Pimviriyakul P, Wongnate T, Tinikul R, Chaiyen P. Microbial degradation of halogenated aromatics: molecular mechanisms and enzymatic reactions. Microb Biotechnol 2020; 13:67-86. [PMID: 31565852 PMCID: PMC6922536 DOI: 10.1111/1751-7915.13488] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 09/01/2019] [Accepted: 09/03/2019] [Indexed: 12/12/2022] Open
Abstract
Halogenated aromatics are used widely in various industrial, agricultural and household applications. However, due to their stability, most of these compounds persist for a long time, leading to accumulation in the environment. Biological degradation of halogenated aromatics provides sustainable, low-cost and environmentally friendly technologies for removing these toxicants from the environment. This minireview discusses the molecular mechanisms of the enzymatic reactions for degrading halogenated aromatics which naturally occur in various microorganisms. In general, the biodegradation process (especially for aerobic degradation) can be divided into three main steps: upper, middle and lower metabolic pathways which successively convert the toxic halogenated aromatics to common metabolites in cells. The most difficult step in the degradation of halogenated aromatics is the dehalogenation step in the middle pathway. Although a variety of enzymes are involved in the degradation of halogenated aromatics, these various pathways all share the common feature of eventually generating metabolites for utilizing in the energy-producing metabolic pathways in cells. An in-depth understanding of how microbes employ various enzymes in biodegradation can lead to the development of new biotechnologies via enzyme/cell/metabolic engineering or synthetic biology for sustainable biodegradation processes.
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Affiliation(s)
- Panu Pimviriyakul
- Department of BiotechnologyFaculty of Engineering and Industrial TechnologySilpakorn UniversityNakhon Pathom73000Thailand
| | - Thanyaporn Wongnate
- School of Biomolecular Science and EngineeringVidyasirimedhi Institute of Science and Technology (VISTEC)Wangchan ValleyRayong21210Thailand
| | - Ruchanok Tinikul
- Department of Biochemistry and Center for Excellence in Protein and Enzyme TechnologyFaculty of ScienceMahidol UniversityBangkok10400Thailand
| | - Pimchai Chaiyen
- School of Biomolecular Science and EngineeringVidyasirimedhi Institute of Science and Technology (VISTEC)Wangchan ValleyRayong21210Thailand
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Ito K, Takagi K, Kataoka R, Kiyota H, Iwasaki A. Dissipation, dehalogenation, and denitration of chloroaromatic compounds by Nocardioides sp. strain PD653: Characterization of the substrate specificity. JOURNAL OF PESTICIDE SCIENCE 2019; 44:171-176. [PMID: 31530974 PMCID: PMC6718357 DOI: 10.1584/jpestics.d19-024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Accepted: 05/21/2019] [Indexed: 06/01/2023]
Abstract
The substrate range of Nocardioides sp. strain PD653, capable of mineralizing hexachlorobenzene, was investigated based on the dissipation of substrates and the liberation of halogen ions. Strain PD653 dehalogenated 10 out of 18 halophenol congeners; however, it could dehalogenate only hexachlorobenzene out of seven halobenzene congeners tested. Moreover, dehalogenation activities were shown for chloronitrobenzenes, along with an increase in the number of substituted chlorine atoms except for 2,3,4,5-tetrachloro-1-nitrobenzene. These results suggested that this strain might be applicable to remediate soil contaminated with these persistent chloroaromatic compounds.
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Affiliation(s)
- Koji Ito
- Hazardous Chemical Division, Institute for Agro-Environmental Sciences, NARO, Kannondai, Tsukuba, Ibaraki 305–8604, Japan
| | - Kazuhiro Takagi
- Hazardous Chemical Division, Institute for Agro-Environmental Sciences, NARO, Kannondai, Tsukuba, Ibaraki 305–8604, Japan
| | - Ryota Kataoka
- Department of Environmental Sciences, University of Yamanashi, Takeda, Kofu, Yamanashi 400–8510, Japan
| | - Hiromasa Kiyota
- Graduate school of Environmental and Life Science, Okayama university, Tsushima, Okayama, Okayama 700–8530, Japan
| | - Akio Iwasaki
- Juntendo Medical Technology Innovation Center, Juntendo University, Hongo, Bunkyo-ku, Tokyo, 113–8421, Japan
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Pimviriyakul P, Surawatanawong P, Chaiyen P. Oxidative dehalogenation and denitration by a flavin-dependent monooxygenase is controlled by substrate deprotonation. Chem Sci 2018; 9:7468-7482. [PMID: 30319747 PMCID: PMC6180312 DOI: 10.1039/c8sc01482e] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Accepted: 08/08/2018] [Indexed: 12/19/2022] Open
Abstract
Enzymes that are capable of detoxifying halogenated phenols (HPs) and nitrophenols (NPs) are valuable for bioremediation and waste biorefining. HadA monooxygenase was found to perform dual functions of oxidative dehalogenation (hydroxylation plus halide elimination) and denitration (hydroxylation plus nitro elimination). Rate constants associated with individual steps of HadA reactions with phenol, halogenated phenols and nitrophenols were measured using combined transient kinetic approaches of stopped-flow absorbance/fluorescence and rapid-quench flow techniques. Density functional theory was used to calculate the thermodynamic and electronic parameters associated with hydroxylation and group elimination steps. These parameters were correlated with the rate constants of hydroxylation, group elimination, and overall product formation to identify factors controlling individual steps. The results indicated that the hydroxylation rate constant is higher when the pK a of the phenolic group is lower, i.e. it is more easily deprotonated, but not higher when the energy gap between the E LUMO of the C4a-hydroperoxy-FAD intermediate and the E HOMO of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the pK a value of the substrate, indicating that the overall reaction is controlled by substrate deprotonation. This step also likely has the highest energy barrier and thus controls the overall process of oxidative dehalogenation and denitration by HadA. This report is the first to identify a key mechanistic factor controlling the enzymatic processes of oxidative dehalogenation and denitration.
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Affiliation(s)
- Panu Pimviriyakul
- School of Biomolecular Science and Engineering , Vidyasirimedhi Institute of Science and Technology (VISTEC) , Wangchan Valley , Rayong , 21210 , Thailand .
- Department of Biochemistry and Center for Excellence in Protein and Enzyme Technology , Faculty of Science , Mahidol University , Bangkok , 10400 , Thailand
| | - Panida Surawatanawong
- Department of Chemistry and Center of Excellence for Innovation in Chemistry , Faculty of Science , Mahidol University , Bangkok , 10400 , Thailand
| | - Pimchai Chaiyen
- School of Biomolecular Science and Engineering , Vidyasirimedhi Institute of Science and Technology (VISTEC) , Wangchan Valley , Rayong , 21210 , Thailand .
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Hampton AS, Mikulski L, Palmer-Brown W, Murphy CD, Sandford G. Evaluation of fluorinated biphenyl ether pro-drug scaffolds employing the chemical-microbial approach. Bioorg Med Chem Lett 2016; 26:2255-8. [PMID: 27020303 DOI: 10.1016/j.bmcl.2016.03.053] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Revised: 03/10/2016] [Accepted: 03/14/2016] [Indexed: 11/17/2022]
Abstract
Incorporation of fluorine in a drug can dramatically affect its metabolism and methods to assess the effect of fluorine substitution on drug metabolism are required for effective drug design. Employing a previously developed chemical-microbial method the metabolism of a series of fluorinated biphenyl ethers was determined. The substrates were synthesized via Ullmann-type condensation reactions between bromotoluene and fluorophenol. The ethers were incubated with the fungus Cunninghamella elegans, which oxidises xenobiotics in an analogous fashion to mammals, generating a number of hydroxylated biphenyl ethers and acids. The propensity of the fluorinated ring to be hydroxylated depended upon the position of the fluorine atom, and the oxidation of the methyl group was observed when it was meta to the oxygen. The experiments demonstrate the applicability of the method to rapidly determine the effect of fluorine substitution on CYP-catalysed biotransformation of pro-drug molecules.
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Affiliation(s)
- Alex S Hampton
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
| | - Lena Mikulski
- UCD School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland
| | - William Palmer-Brown
- UCD School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland
| | - Cormac D Murphy
- UCD School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland.
| | - Graham Sandford
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK.
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Serrano-Plana J, Garcia-Bosch I, Miyake R, Costas M, Company A. SelectiveOrtho-Hydroxylation-Defluorination of 2-Fluorophenolates with a Bis(μ-oxo)dicopper(III) Species. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201405060] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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12
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Serrano-Plana J, Garcia-Bosch I, Miyake R, Costas M, Company A. Selective ortho-hydroxylation-defluorination of 2-fluorophenolates with a bis(μ-oxo)dicopper(III) species. Angew Chem Int Ed Engl 2014; 53:9608-12. [PMID: 25044926 DOI: 10.1002/anie.201405060] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Indexed: 11/06/2022]
Abstract
The bis(μ-oxo)dicopper(III) species [Cu(III) 2 (μ-O)2 (m-XYL(MeAN) )](2+) (1) promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η(2) :η(2) -O2 )dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine.
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Affiliation(s)
- Joan Serrano-Plana
- Grup de Química Bioinorgànica i Supramolecular (QBIS), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071 Girona (Catalonia) (Spain)
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Shaughnessy MJ, Harsanyi A, Li J, Bright T, Murphy CD, Sandford G. Targeted Fluorination of a Nonsteroidal Anti-inflammatory Drug to Prolong Metabolic Half-Life. ChemMedChem 2014; 9:733-6. [DOI: 10.1002/cmdc.201300490] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Indexed: 11/09/2022]
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Form follows function: structural and catalytic variation in the class a flavoprotein monooxygenases. Int J Mol Sci 2012; 13:15601-39. [PMID: 23443084 PMCID: PMC3546652 DOI: 10.3390/ijms131215601] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 11/08/2012] [Accepted: 11/09/2012] [Indexed: 12/02/2022] Open
Abstract
Flavoprotein monooxygenases (FPMOs) exhibit an array of mechanistic solutions to a common chemical objective; the monooxygenation of a target substrate. Each FPMO efficiently couples reduction of a flavin cofactor by NAD(P)H to oxygenation of the target substrate via a (hydro)peroxyflavin intermediate. This purpose of this review is to describe in detail the Class A flavoprotein hydroxylases (FPMO) in the context of the other FPMO classes (B–F). Both one and two component FPMOs are found in nature. Two-component enzymes require, in addition to the monooxygenase, the involvement of a reductase that first catalyzes the reduction of the flavin by NAD(P)H. The Class A and B FPMOs are single-component and manage to orchestrate the same net reaction within a single peptide. The Class A enzymes have, by some considerable margin, the most complete research record. These enzymes use choreographed movements of the flavin ring that facilitate access of the organic substrates to the active site, provide a means for interaction of NADPH with the flavin, offer a mechanism to sequester the dioxygen reduction chemistry from solvent and a means to release the product. The majority of the discrete catalytic events of the catalytic cycle can be observed directly in exquisite detail using spectrophotometric kinetic methods and many of the key mechanistic conclusions are further supported by structural data. This review attempts to compile each of the key observations made for both paradigm and newly discovered examples of Class A FPMOs into a complete catalytic description of one enzymatic turnover.
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Hlouchova K, Rudolph J, Pietari JMH, Behlen LS, Copley SD. Pentachlorophenol hydroxylase, a poorly functioning enzyme required for degradation of pentachlorophenol by Sphingobium chlorophenolicum. Biochemistry 2012; 51:3848-60. [PMID: 22482720 DOI: 10.1021/bi300261p] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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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Affiliation(s)
- Klara Hlouchova
- Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado 80309, USA
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Isolation and characterization of a Rhodococcus strain able to degrade 2-fluorophenol. Appl Microbiol Biotechnol 2011; 95:511-20. [DOI: 10.1007/s00253-011-3696-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2011] [Accepted: 10/31/2011] [Indexed: 10/15/2022]
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Montersino S, Tischler D, Gassner GT, van Berkel WJH. Catalytic and Structural Features of Flavoprotein Hydroxylases and Epoxidases. Adv Synth Catal 2011. [DOI: 10.1002/adsc.201100384] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Murphy CD. Biodegradation and biotransformation of organofluorine compounds. Biotechnol Lett 2009; 32:351-9. [DOI: 10.1007/s10529-009-0174-3] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2009] [Revised: 11/06/2009] [Accepted: 11/09/2009] [Indexed: 10/20/2022]
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Crozier-Reabe KR, Phillips RS, Moran GR. Kynurenine 3-monooxygenase from Pseudomonas fluorescens: substrate-like inhibitors both stimulate flavin reduction and stabilize the flavin-peroxo intermediate yet result in the production of hydrogen peroxide. Biochemistry 2009; 47:12420-33. [PMID: 18954092 DOI: 10.1021/bi8010434] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Kynurenine 3-monooxygenase (KMO) is a flavin-dependent hydroxylase that catalyzes the conversion of l-kynurenine (l-Kyn) to 3-hydroxykynurenine (3OHKyn) in the pathway for tryptophan catabolism. KMO inhibition has been widely suggested as an early treatment for stroke and other neurological disorders that involve ischemia. We have investigated the reductive and the oxidative half-reactions of a stable form of KMO from Pseudomonas fluorescens (KMO). The binding of l-Kyn by the enzyme is relatively slow and involves at least two reversible steps. The rate constant for reduction of the flavin cofactor by NADPH increases by a factor of approximately 2.5 x 10(3) when l-Kyn is bound. The rate of reduction of the KMO.l-Kyn complex is 160 s(-1), and the K(d) for the NADPH complex is 200 microM with charge-transfer absorption bands for the KMO(RED).l-Kyn.NADP(+) complex accumulating after reduction. The reduction potential of KMO is -188 mV and is unresponsive to the addition of l-Kyn or other inhibitory ligands. KMO inhibitors whose structures are reminiscent of l-Kyn such as m-nitrobenzoylalanine and benzoylalanine also stimulate reduction of flavin by NADPH and, in the presence of dioxygen, result in the stoichiometric liberation of hydrogen peroxide, diminishing the perceived therapeutic potential of inhibitors of this type. In the presence of the native substrate, the oxidative half-reaction exhibits triphasic absorbance data. A spectrum consistent with that of a peroxyflavin species accumulates and then decays to yield the oxidized enzyme. This species then undergoes minor spectral changes that, based on flavin difference spectra defined in the presence of 3OHKyn, can be correlated with product release. The oxidative half-reaction observed in the presence of saturating benzoylalanine or m-nitrobenzoylalanine also shows the accumulation of a peroxyflavin species that then decays to yield hydrogen peroxide without hydroxylation.
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Affiliation(s)
- Karen R Crozier-Reabe
- Department of Chemistry and Biochemistry, University of Wisconsin, 3210 North Cramer Street, Milwaukee, Wisconsin 53211-3029, USA
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Ullrich R, Dolge C, Kluge M, Hofrichter M. Pyridine as novel substrate for regioselective oxygenation with aromatic peroxygenase fromAgrocybe aegerita. FEBS Lett 2008; 582:4100-6. [DOI: 10.1016/j.febslet.2008.11.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2008] [Revised: 10/29/2008] [Accepted: 11/09/2008] [Indexed: 10/21/2022]
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Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB. J Bacteriol 2008; 190:5190-8. [PMID: 18502868 DOI: 10.1128/jb.01944-07] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The catabolism of 4-hydroxyacetophenone in Pseudomonas fluorescens ACB is known to proceed through the intermediate formation of hydroquinone. Here, we provide evidence that hydroquinone is further degraded through 4-hydroxymuconic semialdehyde and maleylacetate to beta-ketoadipate. The P. fluorescens ACB genes involved in 4-hydroxyacetophenone utilization were cloned and characterized. Sequence analysis of a 15-kb DNA fragment showed the presence of 14 open reading frames containing a gene cluster (hapCDEFGHIBA) of which at least four encoded enzymes are involved in 4-hydroxyacetophenone degradation: 4-hydroxyacetophenone monooxygenase (hapA), 4-hydroxyphenyl acetate hydrolase (hapB), 4-hydroxymuconic semialdehyde dehydrogenase (hapE), and maleylacetate reductase (hapF). In between hapF and hapB, three genes encoding a putative intradiol dioxygenase (hapG), a protein of the Yci1 family (hapH), and a [2Fe-2S] ferredoxin (hapI) were found. Downstream of the hap genes, five open reading frames are situated encoding three putative regulatory proteins (orf10, orf12, and orf13) and two proteins possibly involved in a membrane efflux pump (orf11 and orf14). Upstream of hapE, two genes (hapC and hapD) were present that showed weak similarity with several iron(II)-dependent extradiol dioxygenases. Based on these findings and additional biochemical evidence, it is proposed that the hapC and hapD gene products are involved in the ring cleavage of hydroquinone.
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Murphy CD. The Application of19F Nuclear Magnetic Resonance to Investigate Microbial Biotransformations of Organofluorine Compounds. OMICS-A JOURNAL OF INTEGRATIVE BIOLOGY 2007; 11:314-24. [PMID: 17883342 DOI: 10.1089/omi.2007.0002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Fluorinated organic compounds, although rare in nature, are significant environmental contaminants owing to the numerous applications for which this class of compounds is employed. It is important that biodegradation of these compounds can be readily assessed in order to provide information on their fate in the environment. Fluorine-19 nuclear magnetic resonance (19F NMR) spectroscopy has emerged as a very useful technique to readily determine the catabolism of fluorinated aromatic compounds by microorganisms, either in whole cell or cell-free systems. The principal advantage of this technique is that fluorinated compounds can be observed directly in the culture supernatant or enzyme assay, without purification or derivatization. In this review an account of the application of 19F NMR in the study of microbial metabolism of organofluorine compounds is presented.
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Affiliation(s)
- Cormac D Murphy
- School of Biomolecular and Biomedical Science, Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin, Ireland.
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Moonen M, Westphal A, Rietjens I, van Berkel W. Enzymatic Baeyer-Villiger Oxidation of Benzaldehydes. Adv Synth Catal 2005. [DOI: 10.1002/adsc.200404307] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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24
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25
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Ahuatzi-chac�n D, Ordorica-morales G, Ruiz-ordaz N, Cristiani-urbina E, Ju�rez-ram�rez C, Gal�ndez-mayer J. Kinetic study of phenol hydroxylase and catechol 1,2-dioxygenase biosynthesis by Candida tropicalis cells grown on different phenolic substrates. World J Microbiol Biotechnol 2004. [DOI: 10.1007/s11274-004-2622-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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26
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Brooks SJ, Doyle EM, Hewage C, Malthouse JPG, Duetz W, O' Connor KE. Biotransformation of halophenols using crude cell extracts of Pseudomonas putida F6. Appl Microbiol Biotechnol 2003; 64:486-92. [PMID: 14647990 DOI: 10.1007/s00253-003-1488-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2003] [Revised: 10/13/2003] [Indexed: 11/24/2022]
Abstract
Crude cell extracts of Pseudomonas putida F6 transformed 4-substituted fluoro-, chloro-, bromo- and iodo-phenol without the exogenous addition of cofactors. The rate of substrate consumption decreased with increasing substituent size (F>Cl>Br>I). Biotransformations resulted in greater than 95% utilisation of the halogenated substrate. Product accumulation was observed in incubations with 4-chloro, 4-bromo- and 4-iodo-phenol. These products were identified as the corresponding 4-substituted catechols. Transformation of 4-fluorophenol did not result in the accumulation of the corresponding catechol; however, manipulation of the reaction conditions by incorporation of ascorbic acid culminated in the formation of 4-fluorocatechol. Cell extracts of P. putida F6 also showed activity towards a 3-substituted phenol, namely 3-fluorophenol, resulting in the formation of a single product, 4-fluorocatechol.
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Affiliation(s)
- S J Brooks
- Department of Industrial Microbiology, University College Dublin, Belfield Dublin 4, Republic of Ireland
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27
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Solyanikova IP, Moiseeva OV, Boeren S, Boersma MG, Kolomytseva MP, Vervoort J, Rietjens IMCM, Golovleva LA, van Berkel WJH. Conversion of 2-fluoromuconate to cis-dienelactone by purified enzymes of Rhodococcus opacus 1cp. Appl Environ Microbiol 2003; 69:5636-42. [PMID: 12957954 PMCID: PMC194941 DOI: 10.1128/aem.69.9.5636-5642.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The present study describes the (19)F nuclear magnetic resonance analysis of the conversion of 3-halocatechols to lactones by purified chlorocatechol 1,2-dioxygenase (ClcA2), chloromuconate cycloisomerase (ClcB2), and chloromuconolactone dehalogenase (ClcF) from Rhodococcus opacus 1cp grown on 2-chlorophenol. The 3-halocatechol substrates were produced from the corresponding 2-halophenols by either phenol hydroxylase from Trichosporon cutaneum or 2-hydroxybiphenyl 3-mono-oxygenase from Pseudomonas azelaica. Several fluoromuconates resulting from intradiol ring cleavage by ClcA2 were identified. ClcB2 converted 2-fluoromuconate to 5-fluoromuconolactone and 2-chloro-4-fluoromuconate to 2-chloro-4-fluoromuconolactone. Especially the cycloisomerization of 2-fluoromuconate is a new observation. ClcF catalyzed the dehalogenation of 5-fluoromuconolactone to cis-dienelactone. The ClcB2 and ClcF-mediated reactions are in line with the recent finding of a second cluster of chlorocatechol catabolic genes in R. opacus 1cp which provides a new route for the microbial dehalogenation of 3-chlorocatechol.
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Affiliation(s)
- Inna P Solyanikova
- G. K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russian Federation
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28
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Netzeva T, Aptula A, Chaudary S, Duffy J, Wayne Schultz T, Schüürmann G, Cronin M. Structure-Activity Relationships for the Toxicity of Substituted Poly-hydroxylated Benzenes toTetrahymena pyriformis: Influence of Free Radical Formation. ACTA ACUST UNITED AC 2003. [DOI: 10.1002/qsar.200330816] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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29
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Moonen M, Fraaije M, Rietjens I, Laane C, van Berkel W. Flavoenzyme-Catalyzed Oxygenations and Oxidations of Phenolic Compounds. Adv Synth Catal 2002. [DOI: 10.1002/1615-4169(200212)344:10<1023::aid-adsc1023>3.0.co;2-t] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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30
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Prenafeta-Boldú FX, Luykx DM, Vervoort J, de Bont JA. Fungal metabolism of toluene: monitoring of fluorinated analogs by (19)F nuclear magnetic resonance spectroscopy. Appl Environ Microbiol 2001; 67:1030-4. [PMID: 11229888 PMCID: PMC92691 DOI: 10.1128/aem.67.3.1030-1034.2001] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We used isomeric fluorotoluenes as model substrates to study the catabolism of toluene by five deuteromycete fungi and one ascomycete fungus capable of growth on toluene as the sole carbon and energy source, as well as by two fungi (Cunninghamella echinulata and Aspergillus niger) that cometabolize toluene. Whole cells were incubated with 2-, 3-, and 4-fluorotoluene, and metabolites were characterized by (19)F nuclear magnetic resonance. Oxidation of fluorotoluene by C. echinulata was initiated either at the aromatic ring, resulting in fluorinated o-cresol, or at the methyl group to form fluorobenzoate. The initial conversion of the fluorotoluenes by toluene-grown fungi occurred only at the side chain and resulted in fluorinated benzoates. The latter compounds were the substrate for the ring hydroxylation and, depending on the fluorine position, were further metabolized up to catecholic intermediates. From the (19)F nuclear magnetic resonance metabolic profiles, we propose that diverse fungi that grow on toluene assimilate toluene by an initial oxidation of the methyl group.
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Affiliation(s)
- F X Prenafeta-Boldú
- Division of Industrial Microbiology, Wageningen University, 6700 EV Wageningen, the Netherlands.
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31
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Eppink MH, Cammaart E, Van Wassenaar D, Middelhoven WJ, van Berkel WJ. Purification and properties of hydroquinone hydroxylase, a FAD-dependent monooxygenase involved in the catabolism of 4-hydroxybenzoate in Candida parapsilosis CBS604. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:6832-40. [PMID: 11082194 DOI: 10.1046/j.1432-1033.2000.01783.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ascomycetous yeast Candida parapsilosis CBS604 catabolizes 4-hydroxybenzoate through the initial formation of hydroquinone (1, 4-dihydroxybenzene). High levels of hydroquinone hydroxylase activity are induced when the yeast is grown on either 4-hydroxybenzoate, 2,4-dihydroxybenzoate, 1,3-dihydroxybenzene or 1, 4-dihydroxybenzene as the sole carbon source. The monooxygenase constitutes up to 5% of the total amount of protein and is purified to apparent homogeneity in three chromatographic steps. Hydroquinone hydroxylase from C. parapsilosis is a homodimer of about 150 kDa with each 76-kDa subunit containing a tightly noncovalently bound FAD. The flavin prosthetic group is quantitatively resolved from the protein at neutral pH in the presence of chaotropic salts. The apoenzyme is dimeric and readily reconstituted with FAD. Hydroquinone hydroxylase from C. parapsilosis catalyzes the ortho-hydroxylation of a wide range of monocyclic phenols with the stoichiometric consumption of NADPH and oxygen. With most aromatic substrates, no uncoupling of hydroxylation occurs. Hydroxylation of monofluorinated phenols is highly regiospecific with a preference for C6 hydroxylation. Binding of phenol highly stimulates the rate of flavin reduction by NADPH. At pH 7.6, 25 degrees C, this step does not limit the rate of overall catalysis. During purification, hydroquinone hydroxylase is susceptible towards limited proteolysis. Proteolytic cleavage does not influence the enzyme dimeric nature but results in relatively stable protein fragments of 55, 43, 35 and 22 kDa. N-Terminal peptide sequence analysis revealed the presence of two nick sites and showed that hydroquinone hydroxylase from C. parapsilosis is structurally related to phenol hydroxylase from Trichosporon cutaneum. The implications of these findings for the catalytic mechanism of hydroquinone hydroxylase are discussed.
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Affiliation(s)
- M H Eppink
- Department of Biomolecular Sciences, Laboratory of Biochemistry, Wageningen University, The Netherlands
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32
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Ridder L, Mulholland AJ, Rietjens IMCM, Vervoort J. A Quantum Mechanical/Molecular Mechanical Study of the Hydroxylation of Phenol and Halogenated Derivatives by Phenol Hydroxylase. J Am Chem Soc 2000. [DOI: 10.1021/ja0007814] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lars Ridder
- Contribution from the Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands, and School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
| | - Adrian J. Mulholland
- Contribution from the Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands, and School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
| | - Ivonne M. C. M. Rietjens
- Contribution from the Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands, and School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
| | - Jacques Vervoort
- Contribution from the Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands, and School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
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33
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Finkelstein ZI, Baskunov BP, Boersma MG, Vervoort J, Golovlev EL, van Berkel WJ, Golovleva LA, Rietjens IM. Identification of fluoropyrogallols as new intermediates in biotransformation of monofluorophenols in Rhodococcus opacus 1cp. Appl Environ Microbiol 2000; 66:2148-53. [PMID: 10788394 PMCID: PMC101467 DOI: 10.1128/aem.66.5.2148-2153.2000] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The transformation of monofluorophenols by whole cells of Rhodococcus opacus 1cp was investigated, with special emphasis on the nature of hydroxylated intermediates formed. Thin-layer chromatography, mass spectrum analysis, and (19)F nuclear magnetic resonance demonstrated the formation of fluorocatechol and trihydroxyfluorobenzene derivatives from each of three monofluorophenols. The (19)F chemical shifts and proton-coupled splitting patterns of the fluorine resonances of the trihydroxyfluorobenzene products established that the trihydroxylated aromatic metabolites contained hydroxyl substituents on three adjacent carbon atoms. Thus, formation of 1,2, 3-trihydroxy-4-fluorobenzene (4-fluoropyrogallol) from 2-fluorophenol and formation of 1,2,3-trihydroxy-5-fluorobenzene (5-fluoropyrogallol) from 3-fluorophenol and 4-fluorophenol were observed. These results indicate the involvement of fluoropyrogallols as previously unidentified metabolites in the biotransformation of monofluorophenols in R. opacus 1cp.
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Affiliation(s)
- Z I Finkelstein
- G. K. Skrybin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Russia
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34
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Bondar VS, Boersma MG, van Berkel WJ, Finkelstein ZI, Golovlev EL, Baskunov BP, Vervoort J, Golovleva LA, Rietjens IM. Preferential oxidative dehalogenation upon conversion of 2-halophenols by Rhodococcus opacus 1G. FEMS Microbiol Lett 1999; 181:73-82. [PMID: 10564791 DOI: 10.1111/j.1574-6968.1999.tb08828.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The regiospecificity of hydroxylation of C2-halogenated phenols by Rhodococcus opacus 1G was investigated. Oxidative defluorination at the C2 position ortho with respect to the hydroxyl moiety was preferred over hydroxylation at the non-fluorinated C6 position for all 2-fluorophenol compounds studied. Initial hydroxylation of 2,3, 5-trichlorophenol resulted in the exclusive formation of 3, 5-dichlorocatechol. These results indicate that, in contrast to all other phenol ortho-hydroxylases studied so far, phenol hydroxylase from R. opacus 1G is capable of catalyzing preferential oxidative defluorination but also oxidative dechlorination.
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Affiliation(s)
- V S Bondar
- Department of Biomolecular Sciences, Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, The Netherlands
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35
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Hartmann S, Hultschig C, Eisenreich W, Fuchs G, Bacher A, Ghisla S. NIH shift in flavin-dependent monooxygenation: mechanistic studies with 2-aminobenzoyl-CoA monooxygenase/reductase. Proc Natl Acad Sci U S A 1999; 96:7831-6. [PMID: 10393907 PMCID: PMC22147 DOI: 10.1073/pnas.96.14.7831] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The flavoprotein 2-aminobenzoyl-CoA monooxygenase/reductase from the eubacterium Azoarcus evansii catalyzes the dearomatization of 2-aminobenzoyl-CoA. The reaction consists in an O2-dependent monooxygenation at the benzene position 5, which is followed immediately by an NADH-dependent hydrogenation of the intermediate at the same catalytic locus. The reaction was studied by 1H, 2H, and 13C NMR spectroscopy of the products. The main product was characterized as 5-oxo-2-aminocyclohex-1-ene-1-carboxyl-CoA by two-dimensional NMR spectroscopy. Thus, [5-2H]2-aminobenzoyl-CoA was converted into [6-2H]5-oxo-2-aminocyclohex-1-ene-1-carboxyl-CoA, indicating a 5 --> 6 shift of the [5-2H] label. Label from NAD2H was transferred to the 3 position of the cyclic eneamine, whereas label from solvent D2O was incorporated into the 4 and the 6 positions of 5-oxo-2-aminocyclohex-1-ene-1-carboxyl-CoA. The labeling pattern is compatible with the monooxygenation proceeding via what is formally an NIH shift, yielding 5-oxo-2-aminocyclohex-1, 3-diene-1-carboxyl-CoA as a protein-bound intermediate. It is suggested that this shift in flavin-dependent monooxygenation may have general validity.
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Affiliation(s)
- S Hartmann
- Fakultät Biologie, Universität Konstanz, P.O. Box 5560-M644, D-78457 Konstanz, Germany
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36
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Boersma MG, Dinarieva TY, Middelhoven WJ, van Berkel WJ, Doran J, Vervoort J, Rietjens IM. 19F nuclear magnetic resonance as a tool to investigate microbial degradation of fluorophenols to fluorocatechols and fluoromuconates. Appl Environ Microbiol 1998; 64:1256-63. [PMID: 9546160 PMCID: PMC106138 DOI: 10.1128/aem.64.4.1256-1263.1998] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A method was developed to study the biodegradation and oxidative biodehalogenation of fluorinated phenols by 19F nuclear magnetic resonance (NMR). Characterization of the 19F NMR spectra of metabolite profiles of a series of fluorophenols, converted by purified phenol hydroxylase, catechol 1,2-dioxygenase, and/or by the yeast-like fungus Exophiala jeanselmei, provided possibilities for identification of the 19F NMR chemical shift values of fluorinated catechol and muconate metabolites. As an example, the 19F NMR method thus defined was used to characterize the time-dependent metabolite profiles of various halophenols in either cell extracts or in incubations with whole cells of E. jeanselmei. The results obtained for these two systems are similar, except for the level of muconates observed. Altogether, the results of the present study describe a 19F NMR method which provides an efficient tool for elucidating the metabolic pathways for conversion of fluorine-containing phenols by microorganisms, with special emphasis on possibilities for biodehalogenation and detection of the type of fluorocatechols and fluoromuconates involved. In addition, the method provides possibilities for studying metabolic pathways in vivo in whole cells.
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Affiliation(s)
- M G Boersma
- Laboratory of Biochemistry, Wageningen Agricultural University, The Netherlands.
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37
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Hansch C, Gao H. Comparative QSAR: Radical Reactions of Benzene Derivatives in Chemistry and Biology. Chem Rev 1997; 97:2995-3060. [PMID: 11851484 DOI: 10.1021/cr9601021] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Corwin Hansch
- Department of Chemistry, Pomona College, Claremont, California 91711
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38
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van der Bolt FJ, van den Heuvel RH, Vervoort J, van Berkel WJ. 19F NMR study on the regiospecificity of hydroxylation of tetrafluoro-4-hydroxybenzoate by wild-type and Y385F p-hydroxybenzoate hydroxylase: evidence for a consecutive oxygenolytic dehalogenation mechanism. Biochemistry 1997; 36:14192-201. [PMID: 9369493 DOI: 10.1021/bi971213c] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The regiospecificity of hydroxylation of tetrafluoro-4-hydroxybenzoate (F4-POHB) by p-hydroxybenzoate hydroxylase (PHBH) and its active site mutant Y385F was investigated by 19F NMR. Evidence is provided that the hydroxylation of F4-POHB is not restricted to the C3 center of the aromatic ring but rather involves sequential oxygenation and dehalogenation steps. The catalytic efficiency of PHBH and Y385F with F4-POHB was optimal near pH 6.5. Below pH 7.0, substantial substrate inhibition occurred. Dianionic F4-POHB was a competent effector, highly stimulating upon binding the rate of flavin reduction by NADPH. Hydroxylation of F4-POHB involved the formation of quinone intermediates as primary products of oxygenolytic defluorination. Ascorbate competed favorably with NADPH for the nonenzymatic reduction of these reactive intermediates and prevented the accumulation of nonspecific oxidation products. 19F NMR showed that the initial aromatic product 2,5,6-trifluoro-3,4-dihydroxybenzoate (F3-DOHB) was further converted to 5,6-difluoro-2,3,4-trihydroxybenzoate (5,6-F2-TOHB). This reaction was most efficient with Y385F. F3-DOHB was not bound in a unique regiospecific orientation as also 2,6-difluoro-3,4, 5-trihydroxybenzoate (2,6-F2-TOHB) was formed. The oxygenolytic dehalogenation of F3-DOHB by PHBH and Y385F is consistent with the electrophilic aromatic substitution mechanism proposed for this class of flavoenzymes. Nucleophilic attack of the carbon centers of F3-DOHB onto the distal oxygen of the electrophilic flavin C(4a)-hydroperoxide occurs when the carbon center has a relatively high HOMO density and is relatively close to the distal oxygen of the flavin C(4a)-hydroperoxide.
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Affiliation(s)
- F J van der Bolt
- Department of Biochemistry, Wageningen Agricultural University, Dreijenlaan 3 6703 HA Wageningen, The Netherlands
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39
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Eppink MH, Boeren SA, Vervoort J, van Berkel WJ. Purification and properties of 4-hydroxybenzoate 1-hydroxylase (decarboxylating), a novel flavin adenine dinucleotide-dependent monooxygenase from Candida parapsilosis CBS604. J Bacteriol 1997; 179:6680-7. [PMID: 9352916 PMCID: PMC179595 DOI: 10.1128/jb.179.21.6680-6687.1997] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
A novel flavoprotein monooxygenase, 4-hydroxybenzoate 1-hydroxylase (decarboxylating), from Candida parapsilosis CBS604 was purified to apparent homogeneity. The enzyme is induced when the yeast is grown on either 4-hydroxybenzoate, 2,4-dihydroxybenzoate, or 3,4-dihydroxybenzoate as the sole carbon source. The purified monooxygenase is a monomer of about 50 kDa containing flavin adenine dinucleotide as weakly bound cofactor. 4-Hydroxybenzoate 1-hydroxylase from C. parapsilosis catalyzes the oxidative decarboxylation of a wide range of 4-hydroxybenzoate derivatives with the stoichiometric consumption of NAD(P)H and oxygen. Optimal catalysis is reached at pH 8, with NADH being the preferred electron donor. By using (18)O2, it was confirmed that the oxygen atom inserted into the product 1,4-dihydroxybenzene is derived from molecular oxygen. 19F nuclear magnetic resonance spectroscopy revealed that the enzyme catalyzes the conversion of fluorinated 4-hydroxybenzoates to the corresponding hydroquinones. The activity of the enzyme is strongly inhibited by 3,5-dichloro-4-hydroxybenzoate, 4-hydroxy-3,5-dinitrobenzoate, and 4-hydroxyisophthalate, which are competitors with the aromatic substrate. The same type of inhibition is exhibited by chloride ions. Molecular orbital calculations show that upon deprotonation of the 4-hydroxy group, nucleophilic reactivity is located in all substrates at the C-1 position. This, and the fact that the enzyme is highly active with tetrafluoro-4-hydroxybenzoate and 4-hydroxy-3-nitrobenzoate, suggests that the phenolate forms of the substrates play an important role in catalysis. Based on the substrate specificity, a mechanism is proposed for the flavin-mediated oxidative decarboxylation of 4-hydroxybenzoate.
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Affiliation(s)
- M H Eppink
- Department of Biochemistry, Wageningen Agricultural University, The Netherlands
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