451
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Eley KL, Crowley PJ, Bugg TD. A solvolytic C-C cleavage reaction of 6-acetoxycyclohexa-2,4-dienones: mechanistic implications for the intradiol catechol dioxygenases. J Org Chem 2001; 66:2091-7. [PMID: 11300906 DOI: 10.1021/jo001669r] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
6-Acetoxycyclohexa-2,4-dienones are found to undergo a rapid reaction in methanol/water under mildly basic conditions to give an acyclic ketoester as the major product for 6-phenyl and 6-methyl substrates. Reaction monitoring by UV spectroscopy indicates the formation of an unsaturated ketone reaction intermediate (lambda(max) 275 nm, R = Ph) and the transient appearance of a highly conjugated species. Reaction of the 6-phenyl substrate (4.95 x 10(-6) s(-1)) is 2-fold faster than the 6-methyl substrate (2.47 x 10(-6) s(-1)). The reaction rate is first order with respect to substrate concentration, and the final step in the reaction is pH-dependent. No cleavage was observed for a substrate lacking an acetyl substituent. A reaction mechanism for C-C cleavage is proposed involving a benzene oxide-oxepin interconversion. The possible relevance to the catalytic mechanism of the intradiol catechol dioxygenases is discussed.
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Affiliation(s)
- K L Eley
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
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452
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Mekmouche Y, Ménage S, Toia-Duboc C, Fontecave M, Galey JB, Lebrun C, Pécaut J. H2O2-Dependent Fe-Catalyzed Oxidations: Control of the Active Species. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010302)113:5<975::aid-ange975>3.0.co;2-p] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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453
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Mekmouche Y, Ménage S, Toia-Duboc C, Fontecave M, Galey JB, Lebrun C, Pécaut J. H 2 O 2 -Dependent Fe-Catalyzed Oxidations: Control of the Active Species. Angew Chem Int Ed Engl 2001; 40:949-952. [PMID: 29712176 DOI: 10.1002/1521-3773(20010302)40:5<949::aid-anie949>3.0.co;2-4] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2000] [Revised: 11/20/2000] [Indexed: 11/09/2022]
Abstract
Manipulation of the coordination sphere of an FeII ion can be used to tune the balance between different catalytic pathways for oxidation (OH. versus iron-based oxidant; see scheme). This reinvestigation of Fenton chemistry uses the iron complex shown as a mechanistic probe.
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Affiliation(s)
- Yasmina Mekmouche
- Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques Université Joseph Fourier/DBMS/CEA, UMR CNRS 5047 17 rue des Martyrs, 38054 Grenoble Cédex 9 (France) Fax: (+33) 476889124
| | - Stéphane Ménage
- Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques Université Joseph Fourier/DBMS/CEA, UMR CNRS 5047 17 rue des Martyrs, 38054 Grenoble Cédex 9 (France) Fax: (+33) 476889124
| | - Carole Toia-Duboc
- Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques Université Joseph Fourier/DBMS/CEA, UMR CNRS 5047 17 rue des Martyrs, 38054 Grenoble Cédex 9 (France) Fax: (+33) 476889124
| | - Marc Fontecave
- Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques Université Joseph Fourier/DBMS/CEA, UMR CNRS 5047 17 rue des Martyrs, 38054 Grenoble Cédex 9 (France) Fax: (+33) 476889124
| | - Jean-Baptiste Galey
- L'Oréal Research Recherche Avancée 1 avenue Eugène Schueller, 93600 Aulnay sous bois (France)
| | - Colette Lebrun
- Service de Chimie Inorganique et Biologique DRFMC CEA-Grenoble (France)
| | - Jacques Pécaut
- Service de Chimie Inorganique et Biologique DRFMC CEA-Grenoble (France)
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454
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Mitchell G, Bartlett DW, Fraser TE, Hawkes TR, Holt DC, Townson JK, Wichert RA. Mesotrione: a new selective herbicide for use in maize. PEST MANAGEMENT SCIENCE 2001; 57:120-8. [PMID: 11455642 DOI: 10.1002/1526-4998(200102)57:2<120::aid-ps254>3.0.co;2-e] [Citation(s) in RCA: 204] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Mesotrione is a new herbicide being developed for the selective pre- and post-emergence control of a wide range of broad-leaved and grass weeds in maize (Zea mays). It is a member of the benzoylcyclohexane-1,3-dione family of herbicides, which are chemically derived from a natural phytotoxin obtained from the Californian bottlebrush plant, Callistemon citrinus. The compound acts by competitive inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), a component of the biochemical pathway that converts tyrosine to plastoquinone and alpha-tocopherol. Mesotrione is an extremely potent inhibitor of HPPD from Arabidopsis thaliana, with a Ki value of c 6-18 pM. It is rapidly taken up by weed species following foliar application, and is distributed within the plants by both acropetal and basipetal movement. Maize is tolerant to mesotrione as a consequence of selective metabolism by the crop plant. Slower uptake of mesotrione, relative to susceptible weed species, may also contribute to its utility as a selective herbicide for use in maize.
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Affiliation(s)
- G Mitchell
- Zeneca Agrochemicals, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6ET, UK.
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455
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456
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Wolfe MD, Parales JV, Gibson DT, Lipscomb JD. Single turnover chemistry and regulation of O2 activation by the oxygenase component of naphthalene 1,2-dioxygenase. J Biol Chem 2001; 276:1945-53. [PMID: 11056161 DOI: 10.1074/jbc.m007795200] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Naphthalene 1,2-dioxygenase (NDOS) is a three-component enzyme that catalyzes cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene formation from naphthalene, O2, and NADH. We have determined the conditions for a single turnover of NDOS for the first time and studied the regulation of catalysis. As isolated, the alpha3beta3 oxygenase component (NDO) has up to three catalytic pairs of metal centers (one mononuclear Fe2+ and one diferric Rieske iron-sulfur cluster). This form of NDO is unreactive with O2. However, upon reduction of the Rieske cluster and exposure to naphthalene and O2, approximately 0.85 cis-diol product per occupied mononuclear iron site rapidly forms. Substrate binding is required for oxygen reactivity. Stopped-flow and chemical quench analyses indicate that the rate constant of the single turnover product-forming reaction significantly exceeds the NDOS turnover number. UV-visible and electron paramagnetic resonance spectroscopies show that during catalysis, one mononuclear iron and one Rieske cluster are oxidized per product formed, satisfying the two-electron reaction stoichiometry. The addition of oxidized or reduced NDOS ferredoxin component (NDF) increases both the product yield and rate of oxidation of formerly unreactive Rieske clusters. The results show that NDO alone catalyzes dioxygenase chemistry, whereas NDF appears to serve only an electron transport role, in this case redistributing electrons to competent active sites.
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Affiliation(s)
- M D Wolfe
- Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
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457
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458
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Belen’kii L, Kruchkovskaya N, Gramenitskaya V. The Literature of Heterocyclic Chemistry, Part VII: 1997–1999. ADVANCES IN HETEROCYCLIC CHEMISTRY 2001. [DOI: 10.1016/s0065-2725(01)79024-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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459
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Elizarova GL, Matvienko LG, Kuzmin AO, Savinova ER, Parmon VN. Copper and iron hydroxides as new catalysts for redox reactions in aqueous solutions. MENDELEEV COMMUNICATIONS 2001. [DOI: 10.1070/mc2001v011n01abeh001379] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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460
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Hubbard BK, Thomas MG, Walsh CT. Biosynthesis of L-p-hydroxyphenylglycine, a non-proteinogenic amino acid constituent of peptide antibiotics. CHEMISTRY & BIOLOGY 2000; 7:931-42. [PMID: 11137816 DOI: 10.1016/s1074-5521(00)00043-0] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND The non-proteinogenic amino acid p-hydroxyphenylglycine is a crucial component of certain peptidic natural products synthesized by a non-ribosomal peptide synthetase mechanism. In particular, for the vancomycin group of antibiotics p-hydroxyphenylglycine plays a structural role in formation of the rigid conformation of the central heptapeptide aglycone in addition to being the site of glycosylation. Initial labeling studies suggested tyrosine was a precursor of p-hydroxyphenylglycine but the specific steps in p-hydroxyphenylglycine biosynthesis remained unknown. Recently, the sequencing of the chloroeremomycin gene cluster from Amycolatopsis orientalis gave new insights into the biosynthetic pathway and allowed for the prediction of a four enzyme pathway leading to L-p-hydroxyphenylglycine from the common metabolite prephenate. RESULTS We have characterized three of the four proposed enzymes of the L-p-hydroxyphenylglycine biosynthetic pathway. The three enzymes are encoded by open reading frames (ORFs) 21, 22 and 17 (ORF21: [PCZA361.1, O52791, CAA11761]; ORF22: [PCZA361. 2, O52792, CAA11762]; ORF17: [PCZA361.25, O52815, CAA11790]), of the chloroeremomycin biosynthetic gene cluster and we show they have p-hydroxymandelate synthase, p-hydroxymandelate oxidase and L-p-hydroxyphenylglycine transaminase activities, respectively. CONCLUSIONS The L-p-hydroxyphenylglycine biosynthetic pathway shown here is proposed to be the paradigm for how this non-proteinogenic amino acid is synthesized by microorganisms incorporating it into peptidic natural products. This conclusion is supported by the finding of homologs for the four L-p-hydroxyphenylpyruvate biosynthetic enzymes in four organisms known to synthesize peptidic natural products that contain p-hydroxyphenylglycine. Three of the enzymes are proposed to function in a cyclic manner in vivo with L-tyrosine being both the amino donor for L-p-hydroxyphenylglycine and a source of p-hydroxyphenylpyruvate, an intermediate in the biosynthetic pathway.
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Affiliation(s)
- B K Hubbard
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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461
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Kahnert A, Kertesz MA. Characterization of a sulfur-regulated oxygenative alkylsulfatase from Pseudomonas putida S-313. J Biol Chem 2000; 275:31661-7. [PMID: 10913158 DOI: 10.1074/jbc.m005820200] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The atsK gene of Pseudomonas putida S-313 was required for growth with alkyl sulfate esters as sulfur source. The AtsK protein was overexpressed in Escherichia coli and purified to homogeneity. Sequence analysis revealed that AtsK was closely related to E. coli taurine dioxygenase (38% amino acid identity). The AtsK protein catalyzed the alpha-ketoglutarate-dependent cleavage of a range of alkyl sulfate esters, with chain lengths ranging from C(4) to C(12), required oxygen and Fe(2+) for activity and released succinate, sulfate, and the corresponding aldehyde as products. Enzyme activity was optimal at pH 7 and was strongly stimulated by ascorbate. Unlike most other characterized alpha-ketoglutarate-dependent dioxygenases, AtsK accepted a range of alpha-keto acids as co-substrates, including alpha-ketoglutarate (K(m) 140 microm), alpha-ketoadipate, alpha-ketovalerate, and alpha-ketooctanoate. The measured K(m) values for hexyl sulfate and SDS were 40 and 34 microm, respectively. The apparent M(r) of the purified enzyme of 121,000 was consistent with a homotetrameric structure, which is unusual for this enzyme superfamily, members of which are usually monomeric or dimeric. The properties and amino acid sequence of the AtsK enzyme thus define it as an unusual oxygenolytic alkylsulfatase and a novel member of the alpha-ketoglutarate-dependent dioxygenase family.
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Affiliation(s)
- A Kahnert
- Institute of Microbiology, Swiss Federal Institute of Technology, ETH-Zentrum, CH-8092 Zürich, Switzerland
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462
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Twilfer H, Sandfort G, Bernhardt FH. Substrate and solvent isotope effects on the fate of the active oxygen species in substrate-modulated reactions of putidamonooxin. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5926-34. [PMID: 10998052 DOI: 10.1046/j.1432-1327.2000.01662.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Using 4-methoxybenzoate monooxygenase from Pseudomonas putida, the substrate deuterium isotope effect on product formation and the solvent isotope effect on the stoichiometry of oxygen uptake, NADH oxidation, product and/or H2O2 (D2O2) formation for tight couplers, partial uncouplers, and uncouplers as substrates were measured. These studies revealed for the true, intrinsic substrate deuterium isotope effect on the oxygenation reaction a k1H/k2H ratio of < 2.0, derived from the inter- and intramolecular substrate isotope effects. This value favours a concerted oxygenation mechanism of the substrate. Deuterium substitution in a tightly coupling substrate initiated a partial uncoupling of oxygen reduction and substrate oxygenation, with release of H2O2 corresponding to 20% of the overall oxygen uptake. This H2O2 (D2O2) formation (oxidase reaction) almost completely disappeared when the oxygenase function was increased by deuterium substitution in the solvent. The electron transfer from NADH to oxygen, however, was not affected by deuterium substitution in the substrate and/or the solvent. With 4-trifluoromethylbenzoate as uncoupling substrate and D2O as solvent, a reduction (peroxidase reaction) of the active oxygen complex was initiated in consequence of its extended lifetime. These additional two electron-transfer reactions to the active oxygen complex were accompanied by a decrease of both NADH oxidation and oxygen uptake rates. These findings lead to the following conclusions: (a) under tightly coupling conditions the rate-limiting step must be the formation time and lifetime of an active transient intermediate within the ternary complex iron/peroxo/substrate, rather than an oxygenative attack on a suitable C-H bond or electron transfer from NADH to oxygen. Water is released after the monooxygenation reaction; (b) under uncoupling conditions there is competition in the detoxification of the active oxygen complex between its protonation (deuteronation), with formation of H2O2 (D2O2) and its further reduction to water. The additional two electron-transfer reactions onto the active oxygen complex then become rate limiting for the oxygen uptake rate.
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Affiliation(s)
- H Twilfer
- Medizinische Biochemie und Molekularbiologie der Universität des Saarlandes, Homburg, Germany
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463
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Sobkowiak A, Naróg D, Sawyer DT. Iron(III, II)-induced activation of dioxygen for the oxygenation of cyclohexene and related unsaturated hydrocarbons. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1381-1169(00)00198-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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464
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Min W, Begley TP, Myllyharju J, Kivirikko KI. Mechanistic Studies on Prolyl-4-Hydroxylase: Demonstration That the Ferryl Intermediate Does Not Exchange with Water. Bioorg Chem 2000; 28:261-265. [PMID: 11133144 DOI: 10.1006/bioo.2000.1182] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Prolyl-4-hydroxylase catalyzes the formation of 4-hydroxyproline in collagens. In contrast to deacetoxy/deacetylcephalosporin C synthase, p-hydroxyphenylpyruvate hydroxylase, lysyl hydroxylase and alpha-ketoisocaproate oxygenase, no incorporation of (18)O-labeled water into the hydroxylated product was found for the human type I prolyl-4-hydroxylase when N-Cbz-Gly-L-Phe-L-Pro-Gly-OEt was used as a substrate. This suggests that the ferryl intermediate for this enzyme is not solvent accessible. Copyright 2000 Academic Press.
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Affiliation(s)
- W Min
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, 14853
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465
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Kreisberg-Zakarin R, Borovok I, Yanko M, Frolow F, Aharonowitz Y, Cohen G. Structure-function studies of the non-heme iron active site of isopenicillin N synthase: some implications for catalysis. Biophys Chem 2000; 86:109-18. [PMID: 11026676 DOI: 10.1016/s0301-4622(00)00123-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Isopenicillin N synthase (IPNS) is a non-heme ferrous iron-dependent oxygenase that catalyzes the ring closure of delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-valine (ACV) to form isopenicillin N. Spectroscopic studies and the crystal structure of IPNS show that the iron atom in the active species is coordinated to two histidine and one aspartic acid residues, and to ACV, dioxygen and H2O. We previously showed by site-directed mutagenesis that residues His212, Asp214 and His268 in the IPNS of Streptomyces jumonjinensis are essential for activity and correspond to the iron ligands identified by crystallography. To evaluate the importance of the nature of the protein ligands for activity, His214 and His268 were exchanged with asparagine, aspartic acid and glutamine, and Asp214 replaced with glutamic acid, histidine and cysteine, each of which has the potential to bind iron. Only the Asp214Glu mutant retained activity, approximately 1% that of the wild type. To determine the importance of the spatial arrangement of the protein ligands for activity, His212 and His268 were separately exchanged with Asp214; both mutant enzymes were completely defective. These findings establish that IPNS activity depends critically on the presence of two histidine and one carboxylate ligands in a unique spatial arrangement within the active site. Molecular modeling studies of the active site employing the S. jumonjinensis IPNS crystal structure support this view. Measurements of iron binding by the wild type and the Asp214Glu, Asp214His and Asp214Cys-modified proteins suggest that Asp214 may have a role in catalysis as well as in iron coordination.
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Affiliation(s)
- R Kreisberg-Zakarin
- Department of Molecular Microbiology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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466
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Wu M, Moon HS, Pirskanen A, Myllyharju J, Kivirikko KI, Begley TP. Mechanistic studies on prolyl-4-hydroxylase: the vitamin C requiring uncoupled oxidation. Bioorg Med Chem Lett 2000; 10:1511-4. [PMID: 10915038 DOI: 10.1016/s0960-894x(00)00224-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
A deuterated substrate for the human type I prolyl-4-hydroxylase was synthesized and its V/K deuterium isotope effect was determined to be 3.4 +/- 0.2. This isotope effect was attributed to the uncoupled oxidation. A dehydroproline containing tetrapeptide was also found to stimulate the uncoupled oxidation.
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Affiliation(s)
- M Wu
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
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467
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Fitzpatrick PF. The aromatic amino acid hydroxylases. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2000; 74:235-94. [PMID: 10800597 DOI: 10.1002/9780470123201.ch6] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
The enzymes phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase constitute the family of pterin-dependent aromatic amino acid hydroxylases. Each enzyme catalyzes the hydroxylation of the aromatic side chain of its respective amino acid substrate using molecular oxygen and a tetrahydropterin as substrates. Recent advances have provided insights into the structures, mechanisms, and regulation of these enzymes. The eukaryotic enzymes are homotetramers comprised of homologous catalytic domains and discrete regulatory domains. The ligands to the active site iron atom as well as residues involved in substrate binding have been identified from a combination of structural studies and site-directed mutagenesis. Mechanistic studies with nonphysiological and isotopically substituted substrates have provided details of the mechanism of hydroxylation. While the complex regulatory properties of phenylalanine and tyrosine hydroxylase are still not fully understood, effects of regulation on key kinetic parameters have been identified. Phenylalanine hydroxylase is regulated by an interaction between phosphorylation and allosteric regulation by substrates. Tyrosine hydroxylase is regulated by phosphorylation and feedback inhibition by catecholamines.
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Affiliation(s)
- P F Fitzpatrick
- Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128, USA
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468
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Abstract
Understanding the early genesis of new enzymatic functions is one of the challenges in protein design, mechanistic enzymology, and molecular evolution. We have experimentally mimicked starting points in this process by introducing primitive iron and oxygen binding sites at various locations in thioredoxin, a small protein lacking metal centers, by using computational design. These rudimentary active sites show emerging enzymatic activities that select to varying degrees between different oxygen chemistries. Even within these nascent enzymes, mechanisms by which different reactions are controlled can be discerned. These involve both stabilizing and destabilizing interactions imposed on the metal center by the surrounding protein matrix.
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Affiliation(s)
- D E Benson
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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469
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470
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Imbeault NY, Powlowski JB, Colbert CL, Bolin JT, Eltis LD. Steady-state kinetic characterization and crystallization of a polychlorinated biphenyl-transforming dioxygenase. J Biol Chem 2000; 275:12430-7. [PMID: 10777527 DOI: 10.1074/jbc.275.17.12430] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The oxygenase component of biphenyl dioxygenase (BPDO) from Comamonas testosteroni B-356 dihydroxylates biphenyl and some polychlorinated biphenyls (PCBs), thereby initiating their degradation. Overexpressed, anaerobically purified BPDO had a specific activity of 4.9 units/mg, and its oxygenase component appeared to contain a full complement of Fe(2)S(2) center and catalytic iron. Oxygenase crystals in space group R3 were obtained under anaerobic conditions using polyethylene glycol as the precipitant. X-ray diffraction was measured to 1.6 A. Steady-state kinetics assays demonstrated that BPDO had an apparent k(cat)/K(m) for biphenyl of (1.2 +/- 0.1) x 10(6) M(-1) s(-1) in air-saturated buffer. Moreover, BPDO transformed dichlorobiphenyls (diClBs) in the following order of apparent specificities: 3,3'- > 2,2'- > 4, 4'-diClB. Strikingly, the ability of BPDO to utilize O(2) depended strongly on the biphenyl substrate: k(cat)/K(m(O(2))) = (3.6 +/- 0. 3), (0.06 +/- 0.02), and (0.4 +/- 0.07) x 10(5) M(-1) s(-1) in the presence of biphenyl and 2,2'- and 3,3'-diClBs, respectively. Moreover, biphenyl/O(2) consumed was 0.97, 0.44, 0.63, and 0.48 in the presence of biphenyl and 2,2'-, 3,3'-, and 4,4'-diClBs, respectively. Within experimental error, the balance of consumed O(2) was detected as H(2)O(2). Thus, PCB congeners such as 2, 2'-diClB exact a high energetic cost, produce a cytotoxic compound (H(2)O(2)), and can inhibit degradation of other congeners. Each of these effects would be predicted to inhibit the aerobic microbial catabolism of PCBs.
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Affiliation(s)
- N Y Imbeault
- Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec H3G 1M8, Canada
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471
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Bencini A, Bill E, Mariotti F, Totti F, Scozzafava A, Vargas A. Density functional description of the early stages of the dioxygenation of [(MeC(CH2PPh2)3)M(catecholate)]+ complexes [M = Co(III), Ir(III)]: toward a rationalization of the catalytic mechanism of ring-opening dioxygenases. Inorg Chem 2000; 39:1418-25. [PMID: 12526444 DOI: 10.1021/ic990633i] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Density Functional Theory (DFT) has been applied to characterize the early stages of the reaction of dioxygenation of [(triphos)M(catecholate)]+ complexes [M = Co(III), Ir(III); triphos = MeC(CH2PPh2)3], which have been considered to be models of ring-opening dioxygenases. The structural features of the starting complexes and of the intermediate complexes formed by addition of O2 to the coordinated catecholato ion are well reproduced. The calculations showed that this preliminary stage can be obtained only when the oxygen molecule attacks the molecule on the catecholato site.
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Affiliation(s)
- A Bencini
- Dipartimento di Chimica, Università di Firenze, Firenze, Italy. Max-Planck-Institut für Strahlenchemie, Mülheim, Germany
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472
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(Catecholato)iron(III) complexes with tetradentate tripodal ligands containing substituted phenol and pyridine units as structural and functional model complexes for the catechol-bound intermediate of intradiol-cleaving catechol dioxygenases. Inorganica Chim Acta 2000. [DOI: 10.1016/s0020-1693(99)00604-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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473
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Duelund L, Toftlund H. Electron paramagnetic resonance characteristics of some non-heme low-spin iron(III) complexes. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2000; 56A:331-340. [PMID: 10727150 DOI: 10.1016/s1386-1425(99)00243-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We have recorded the powder EPR-spectra of some near octahedral iron(III) complexes with tridentate ligands donors and analysed their spectra with simple ligand field analysis and for some cases with the angular overlap model (AOM). We have determined the electron praramagnetic resonance (EPR) characteristic of bis 1,4,7-triazacyclonane iron(III)chloride at 4 K and found that it was similar to the characteristics of the so-called 'highly anisotropic low spin' complexes. We have recorded the powder spectra of bis (2,6-bis(benzimidazoly-2-yl)pyridine) iron(III) perchlorate and made an AOM-analyses of the structural similar complex bis-(2,6 (N-carbamoyl)-pyridine) iron(III). With a combination of ligand field analyses and AOM, we could determine the pi-donor properties of these ligands. The same approach have been used to determine the pi-donor properties of the hydroperoxo ligand. Finally we have recorded the powder EPR-spectrum of [Fe(CN)6]3- doped in K3[Co(CN)6] and [Co(NH3)6][Co(CN)6] at 4 and 100 K and in water at 4 K. The spectra are interpreted as the effect of a dynamic Jahn-Teller distortion.
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Affiliation(s)
- L Duelund
- Department of Chemistry, University of Southern Denmark, Odense University
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474
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Lee HJ, Lloyd MD, Harlos K, Schofield CJ. The effect of cysteine mutations on recombinant deacetoxycephalosporin C synthase from S. clavuligerus. Biochem Biophys Res Commun 2000; 267:445-8. [PMID: 10623639 DOI: 10.1006/bbrc.1999.1957] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cysteines 100, 155, and 197 of recombinant deacetoxycephalosporin C synthase were mutated to alanine residues. The C100A mutant had properties similar to those of the wild-type enzyme, but mutation of Cys-155 and Cys-197 reduced enzyme activity with penicillin N and penicillin G to different extents.
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Affiliation(s)
- H J Lee
- Oxford Centre for Molecular Sciences, Dyson Perrins Laboratory, South Parks Road, Oxford, OX1 3QY, United Kingdom
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475
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Mizuno N, Misono M, Nishiyama Y, Seki Y, Kiyoto I, Nozaki C. Comparison of catalytic activity and efficiency of hydrogen peroxide utilization for di-iron-containing silicotungstate with those for iron containing complexes and the oxidation of methane and ethane. RESEARCH ON CHEMICAL INTERMEDIATES 2000. [DOI: 10.1163/156856700x00237] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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476
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Two-Oxoacid-Dependent Dioxygenases: Inefficient Enzymes or Evolutionary Driving Force? ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s0079-9920(00)80009-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/16/2023]
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477
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Williams NK, Klinman JP. Whence topa? Models for the biogenesis of topa quinone in copper amine oxidases. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1381-1177(99)00071-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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478
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Ogihara T, Hikichi* S, Akita* M, Uchida T, Kitagawa T, Moro-oka* Y. An approach to the O2 activating mononuclear non-heme Fe enzymes: structural characterization of Fe(II)–acetato complex and formation of alkylperoxoiron(III) species with the highly hindered hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate. Inorganica Chim Acta 2000. [DOI: 10.1016/s0020-1693(99)00337-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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479
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Morgenstern-Badarau I, Lambert F, Philippe Renault J, Cesario M, Maréchal JD, Maseras F. Amine conformational change and spin conversion induced by metal-assisted ligand oxidation: from the seven-coordinate iron(II)–TPAA complex to the two oxidized iron(II)–(py)3tren isomers. Characterization, crystal structures, and density functional study. Inorganica Chim Acta 2000. [DOI: 10.1016/s0020-1693(99)00363-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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480
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Wang CCY, Ho DM, Groves JT. Models of Nitric Oxide Synthase: Iron(III) Porphyrin-Catalyzed Oxidation of Fluorenone Oxime to Nitric Oxide and Fluorenone. J Am Chem Soc 1999. [DOI: 10.1021/ja992373+] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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481
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Funabiki T, Yamazaki T. Mechanism of oxygenative cleavage of catechols by nonheme iron complexes in relevance to catechol dioxygenases studied by quantum chemical calculations. ACTA ACUST UNITED AC 1999. [DOI: 10.1016/s1381-1169(99)00198-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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482
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Schofield CJ, Zhang Z. Structural and mechanistic studies on 2-oxoglutarate-dependent oxygenases and related enzymes. Curr Opin Struct Biol 1999; 9:722-31. [PMID: 10607676 DOI: 10.1016/s0959-440x(99)00036-6] [Citation(s) in RCA: 292] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Mononuclear nonheme-Fe(II)-dependent oxygenases comprise an extended family of oxidising enzymes, of which the 2-oxoglutarate-dependent oxygenases and related enzymes are the largest known subgroup. Recent crystallographic and mechanistic studies have helped to define the overall fold of the 2-oxoglutarate-dependent enzymes and have led to the identification of coordination chemistry closely related to that of other nonheme-Fe(II)-dependent oxygenases, suggesting related mechanisms for dioxygen activation that involve iron-mediated electron transfer.
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Affiliation(s)
- C J Schofield
- Department of Chemistry, The Oxford Centre for Molecular Sciences, The Dyson Perrins Laboratory, Oxford, OX1 3QY, UK
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483
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Fox OD, Dalley NK, Harrison RG. Structure and Small Molecule Binding of a Tetranuclear Iron(II) Resorc[4]arene-Based Cage Complex. Inorg Chem 1999. [DOI: 10.1021/ic990834m] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- O. Danny Fox
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
| | - N. Kent Dalley
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
| | - Roger G. Harrison
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
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484
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Weiner H, Finke RG. An All-Inorganic, Polyoxometalate-Based Catechol Dioxygenase That Exhibits >100 000 Catalytic Turnovers. J Am Chem Soc 1999. [DOI: 10.1021/ja991503b] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Heiko Weiner
- Contribution from the Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
| | - Richard G. Finke
- Contribution from the Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
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485
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Johnson MD, Sharma KD. Kinetics and mechanism of the reduction of ferrate by one-electron reductants. Inorganica Chim Acta 1999. [DOI: 10.1016/s0020-1693(99)00214-5] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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486
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Collman JP, Zhong M, Wang Z. A general route to 4-imidazolyl-containing multidentate ligands for biomimetic studies. Org Lett 1999; 1:949-51. [PMID: 10823226 DOI: 10.1021/ol990201b] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[formula: see text] 4-iodo-1-tritylimidazole undergoes magnesium-iodine exchange with a Grignard reagent to give selectively the 4-magnesioimidazole derivative, which reacts with esters to form a variety of poly-4-imidazolyl carbinol compounds in 40-79% yields. A wide range of bi-, tri-, and pentadentate ligands featuring 4-substituted imidazole units have been efficiently synthesized.
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Affiliation(s)
- J P Collman
- Department of Chemistry, Stanford University, California 94305-5080, USA.
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487
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Havranek M, Singh A, Sames D. Evolution and Study of Polymer-Supported Metal Catalysts for Oxygen Atom Transfer: Oxidation of Alkanes and Alkenes by Diamide Manganese Complexes. J Am Chem Soc 1999. [DOI: 10.1021/ja991336f] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Miroslav Havranek
- Department of Chemistry, Columbia University New York, New York 10027
| | - Arun Singh
- Department of Chemistry, Columbia University New York, New York 10027
| | - Dalibor Sames
- Department of Chemistry, Columbia University New York, New York 10027
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488
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Claussen CA, Long EC. Nucleic Acid recognition by metal complexes of bleomycin. Chem Rev 1999; 99:2797-816. [PMID: 11749501 DOI: 10.1021/cr980449z] [Citation(s) in RCA: 207] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- C A Claussen
- Department of Chemistry, Purdue School of Science, Indiana University Purdue University-Indianapolis, Indianapolis, Indiana 46202-3274
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489
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Walsh JG, Furlong PJ, Byrne LA, Gilheany DG. Studies in the oxidative ring-opening of catechols and o-benzoquinones. Lead tetraacetate versus the copper(I) chloride/pyridine/methanol system. Tetrahedron 1999. [DOI: 10.1016/s0040-4020(99)00651-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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490
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Wada A, Ogo S, Watanabe Y, Mukai M, Kitagawa T, Jitsukawa K, Masuda H, Einaga H. Synthesis and Characterization of Novel Alkylperoxo Mononuclear Iron(III) Complexes with a Tripodal Pyridylamine Ligand: A Model for Peroxo Intermediates in Reactions Catalyzed by Non-Heme Iron Enzymes. Inorg Chem 1999; 38:3592-3593. [PMID: 11671111 DOI: 10.1021/ic9900298] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Akira Wada
- Department of Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan, and Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan
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491
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Balogh-Hergovich É, Kaizer J, Speier G, Fülöp V, Párkányi L. Quercetin 2,3-Dioxygenase Mimicking Ring Cleavage of the Flavonolate Ligand Assisted by Copper. Synthesis and Characterization of Copper(I) Complexes [Cu(PPh3)2(fla)] (fla = Flavonolate) and [Cu(PPh3)2(O-bs)] (O-bs = O-Benzoylsalicylate). Inorg Chem 1999. [DOI: 10.1021/ic990175d] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Éva Balogh-Hergovich
- Department of Organic Chemistry, University of Veszprém, 8201 Veszprém, Hungary, Research Group for Petrochemistry of the Hungarian Academy of Sciences 8201 Veszprém, Hungary, and Central Research Institute of Chemistry of the Hungarian Academy of Sciences, 1525 Budapest, Hungary
| | - József Kaizer
- Department of Organic Chemistry, University of Veszprém, 8201 Veszprém, Hungary, Research Group for Petrochemistry of the Hungarian Academy of Sciences 8201 Veszprém, Hungary, and Central Research Institute of Chemistry of the Hungarian Academy of Sciences, 1525 Budapest, Hungary
| | - Gábor Speier
- Department of Organic Chemistry, University of Veszprém, 8201 Veszprém, Hungary, Research Group for Petrochemistry of the Hungarian Academy of Sciences 8201 Veszprém, Hungary, and Central Research Institute of Chemistry of the Hungarian Academy of Sciences, 1525 Budapest, Hungary
| | - Vilmos Fülöp
- Department of Organic Chemistry, University of Veszprém, 8201 Veszprém, Hungary, Research Group for Petrochemistry of the Hungarian Academy of Sciences 8201 Veszprém, Hungary, and Central Research Institute of Chemistry of the Hungarian Academy of Sciences, 1525 Budapest, Hungary
| | - László Párkányi
- Department of Organic Chemistry, University of Veszprém, 8201 Veszprém, Hungary, Research Group for Petrochemistry of the Hungarian Academy of Sciences 8201 Veszprém, Hungary, and Central Research Institute of Chemistry of the Hungarian Academy of Sciences, 1525 Budapest, Hungary
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492
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Chen K, Que, Jr. L. Ein Nicht-Häm-Eisenkomplex als Katalysator für diecis-Dihydroxylierung von Olefinen: ein funktionelles Modell für Rieske-Dioxygenasen. Angew Chem Int Ed Engl 1999. [DOI: 10.1002/(sici)1521-3757(19990802)111:15<2365::aid-ange2365>3.0.co;2-q] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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493
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Weiner H, Hayashi Y, Finke RG. A polyoxoanion-based iron(II) catechol extradiol dioxygenase: oxygenation of 3,5-di-tert-butylcatechol by the polyoxoanion-supported iron(II) complex (n-Bu4N)7[(CH3CN)xFeII·P2W15Nb3O62]. Inorganica Chim Acta 1999. [DOI: 10.1016/s0020-1693(99)00161-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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494
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Brandts JA, Janssen MD, Hogerheide MP, Boersma J, Spek AL, van Koten G. Bisphenolate iron(II) complexes with intramolecularly coordinating nitrogen Lewis bases. Inorganica Chim Acta 1999. [DOI: 10.1016/s0020-1693(99)00157-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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495
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Novel iron(III) complexes with imidazole containing tripodal ligands as model systems for catechol dioxygenases. Inorganica Chim Acta 1999. [DOI: 10.1016/s0020-1693(99)00129-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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496
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Rocklin AM, Tierney DL, Kofman V, Brunhuber NM, Hoffman BM, Christoffersen RE, Reich NO, Lipscomb JD, Que L. Role of the nonheme Fe(II) center in the biosynthesis of the plant hormone ethylene. Proc Natl Acad Sci U S A 1999; 96:7905-9. [PMID: 10393920 PMCID: PMC22160 DOI: 10.1073/pnas.96.14.7905] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The final step of ethylene biosynthesis in plants is catalyzed by the enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACCO). In addition to ACC, Fe(II), O2, CO2, and ascorbate are required for in vitro enzyme activity. Direct evidence for the role of the Fe(II) center in the recombinant avocado ACCO has now been obtained through formation of enzyme.(substrate or cofactor).NO complexes. These NO adducts convert the normally EPR-silent ACCO complexes into EPR-active species with structural properties similar to those of the corresponding O2 complexes. It is shown here that the ternary Fe(II)ACCO.ACC.NO complex is readily formed, but no Fe(II)ACCO.ascorbate.NO complex could be observed, suggesting that ascorbate and NO are mutually exclusive in the active site. The binding modes of ACC and the structural analog alanine specifically labeled with 15N or 17O were examined by using Q-band electron nuclear double resonance (ENDOR). The data indicate that these molecules bind directly to the iron through both the alpha-amino and alpha-carboxylate groups. These observations are inconsistent with the currently favored mechanism for ACCO, in which it is proposed that both ascorbate and O2 bind to the iron as a step in O2 activation. We propose a different mechanism in which the iron serves instead to simultaneously bind ACC and O2, thereby fixing their relative orientations and promoting electron transfer between them to initiate catalysis.
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Affiliation(s)
- A M Rocklin
- Departments of Chemistry and Biochemistry, Molecular Biology and Biophysics and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA
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497
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Bärsch S, Kretzschmar I, Schröder D, Schwarz H, Armentrout PB. Hydrodesulfurization of FeS+: Predominance of Kinetic over Thermodynamic Control. J Phys Chem A 1999. [DOI: 10.1021/jp990244+] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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498
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Aukauloo A, Ottenwaelder X, Ruiz R, Poussereau S, Pei Y, Journaux Y, Fleurat P, Volatron F, Cervera B, Muñoz MC. A Square-Planar Dinickel(II) Complex with a Noninnocent Dinucleating Oxamate Ligand: Evidence for a Ligand Radical Species. Eur J Inorg Chem 1999. [DOI: 10.1002/(sici)1099-0682(199907)1999:7<1067::aid-ejic1067>3.0.co;2-7] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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499
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The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide. Russ Chem Bull 1999. [DOI: 10.1007/bf02494640] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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500
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Neese F, Solomon EI. MCD C-Term Signs, Saturation Behavior, and Determination of Band Polarizations in Randomly Oriented Systems with Spin S >/= (1)/(2). Applications to S = (1)/(2) and S = (5)/(2). Inorg Chem 1999; 38:1847-1865. [PMID: 11670957 DOI: 10.1021/ic981264d] [Citation(s) in RCA: 196] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The magnetic circular dichroism (MCD) properties of a spin-allowed transition from an orbitally nondegenerate ground state manifold A to an orbitally nondegenerate excited state manifold J in the presence of spin-orbit coupling (SOC) are derived for any S >/= (1)/(2). Three physically distinct mechanisms are identified that lead to MCD intensity and depend on SOC between excited states which leads to a sum rule and SOC between the ground state and other excited states that leads to deviations from the sum rule. The model is valid for any symmetry of the magnetic coupling tensors and arbitrary transition polarizations. The S = (1)/(2) case is analytically solved, and the determination of linear polarizations from MCD saturation magnetization data is discussed. For all mechanisms the MCD intensity is proportional to the spin-expectation values of the ground state sublevels which are conveniently generated from a spin-Hamiltonian (SH). For Kramers systems with large zero-field splittings (ZFSs) this allows the contribution from each Kramers doublet to the total MCD intensity to be related through their effective g-values, therefore significantly reducing the number of parameters required to analyze experimental data. The behavior of high-spin systems is discussed in the limits of weak, intermediate, and strong ZFS relative to the Zeeman energy. The model remains valid in the important case of intermediate ZFS where the ground state sublevels may cross as a function of applied magnetic field and there are significant off-axis contributions to the MCD intensity due to a change of the electron spin quantization axis. The model permits calculation of MCD C-term signs from molecular wave functions, and explicit expressions are derived in terms of MOs for S = (1)/(2) and S = (5)/(2). Two examples from the literature are analyzed to demonstrate how the C-term signs can be evaluated by a graphical method that gives insight into their physical origin.
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Affiliation(s)
- Frank Neese
- Department of Chemistry, Stanford University, Stanford, California 94305
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