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Bray RC. The reactions and the structures of molybdenum centers in enzymes. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 51:107-65. [PMID: 6255771 DOI: 10.1002/9780470122969.ch3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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2
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Rosemeyer H, Kaiser K, Seela F, Zabel V, Saenger W. Spontane Öffnung des Pyrimidinringes in Pyrrolo[2,3-d]pyrimidinen nach intramolekularer Acylierung. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19850680226] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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3
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Xanthine and hypoxanthine sensors based on xanthine oxidase immobilized on a CuPtCl6 chemically modified electrode and liquid chromatography electrochemical detection. Anal Chim Acta 2000. [DOI: 10.1016/s0003-2670(00)00775-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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4
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Hu S, Liu CC. Amperometric sensor for fish freshness based on immobilized multi-enzyme modified electrode. ELECTROANAL 1997. [DOI: 10.1002/elan.1140091602] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Hernández B, Orozco M, Luque FJ. Tautomerism of xanthine and alloxanthine: a model for substrate recognition by xanthine oxidase. J Comput Aided Mol Des 1996; 10:535-44. [PMID: 9007687 DOI: 10.1007/bf00134177] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Tautomerism of neutral xanthine and alloxanthine has been examined both in the gas phase and in aqueous solution. The tautomeric preference in the gas phase has been studied by means of semiempirical and ab initio quantum-mechanical computations with inclusion of correlation effects at the Møller-Plesset level, and from density-functional calculations. The influence of solvent on the relative stability between tautomers has been estimated from self-consistent reaction field calculations performed with different models. The results provide a detailed picture of tautomerism for these biologically relevant purine bases. The functional implications in the recognition by xanthine oxidase are analyzed from inspection of the interaction patterns of the most stable tautomeric forms. A model for the recognition of these purine derivatives in the enzyme binding site is discussed.
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Affiliation(s)
- B Hernández
- Department of Biochemistry and Molecular Biology, Faculty of Chemistry, University of Barcelona, Spain
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Hernández B, Luque FJ, Orozco M. Tautomerism of Xanthine Oxidase Substrates Hypoxanthine and Allopurinol. J Org Chem 1996. [DOI: 10.1021/jo960133w] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Begoña Hernández
- Departament de Bioquímica i Biologia Molecular, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1, Barcelona 08028, Spain, and Departament de Farmàcia, Unitat Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Avgda, Diagonal s/n, Barcelona 08028, Spain
| | - Francisco J. Luque
- Departament de Bioquímica i Biologia Molecular, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1, Barcelona 08028, Spain, and Departament de Farmàcia, Unitat Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Avgda, Diagonal s/n, Barcelona 08028, Spain
| | - Modesto Orozco
- Departament de Bioquímica i Biologia Molecular, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1, Barcelona 08028, Spain, and Departament de Farmàcia, Unitat Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Avgda, Diagonal s/n, Barcelona 08028, Spain
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8
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Xanthine and hypoxanthine sensors based on xanthine oxidase immobilized in poly(mercapto-p-benzoquinone) film. J Electroanal Chem (Lausanne) 1996. [DOI: 10.1016/0022-0728(96)04553-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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9
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Rosskopf R, Rainer H, Giesecke D. [Purine and pyrimidine metabolites for the estimation of rumen metabolism: HPLC analysis in milk and blood plasma]. ARCHIV FUR TIERERNAHRUNG 1991; 41:411-26. [PMID: 1888272 DOI: 10.1080/17450399109428482] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In milk and blood plasma samples of 6 German Simmental and 12 German Black and White heifers it was investigated, whether purine and pyrimidine compounds are suitable indicators of the microbial protein synthesis in the rumen. Therefore the secreted quantities in milk and the concentration in blood plasma are correlated with energy intake. The results indicated significant correlation coefficients for both the secretion quantity of allantoin in milk (r = 0.942) and the concentration of allantoin in blood plasma (r = 0.694). Other investigated compounds appeared more suitable for evaluating the mammary gland metabolism (uridine-lactose synthesis, pseudouridine-protein synthesis). In an experiment with 7 male castrated pigmy goats subjected to a four-day fasting period the decrease of plasma allantoin, which was already apparent after 12 hours of fasting, was closely correlated with the increase of plasma free fatty acids.
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Affiliation(s)
- R Rosskopf
- Institut für Physiologie, Physiologische Chemie und Ernährungsphysiologie, Tierärztliche Fakultät der Ludwig-Maximilians-Universität München
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Rosemeyer H, Kaiser K, Seela F. Dextran-linked 7-deazaguanine - a polymer-bound inhibitor of xanthine oxidase. Int J Biol Macromol 1987. [DOI: 10.1016/0141-8130(87)90054-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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12
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De Meester JWG, Kraus W, Van Der Plas HC, Brons HJ, Middelhoven WJ. Synthesis of 3-alkyl-6-phenyl-4(3H)-pteridinones and their 8-oxides. Potential substrates of xanthine oxidase. J Heterocycl Chem 1987. [DOI: 10.1002/jhet.5570240436] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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13
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Zbaida S, Kariv R, Fischer P, Gilhar D. Reactions of theophylline, theobromine and caffeine with Fenton's reagent--simulation of hepatic metabolism. Xenobiotica 1987; 17:617-21. [PMID: 3604265 DOI: 10.3109/00498258709043968] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Theophylline and caffeine undergo N-demethylation and hydroxylation by Fenton's reagent to give uric acid derivatives; theophylline is oxidized mainly to 1-methyluric acid, and 1,3-dimethyluric acid and 1-methyluric acid are the major products obtained from caffeine. Theobromine undergoes predominantly N-demethylation to give 7-methylxanthine. The nature of the products indicate that these reactions simulate hepatic drug metabolism.
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14
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Beedham C. Molybdenum hydroxylases: biological distribution and substrate-inhibitor specificity. PROGRESS IN MEDICINAL CHEMISTRY 1987; 24:85-127. [PMID: 3332920 DOI: 10.1016/s0079-6468(08)70420-x] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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15
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Rosemeyer H, Kretschmer U, Seela F. Cyclisation of 7-Deazaxanthine-9-propionic Acid to an Active-Site-Directed, Irreversibly Acting Inhibitor of Xanthine Oxidase. Helv Chim Acta 1985. [DOI: 10.1002/hlca.19850680811] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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16
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Folkers G, Höltje HD. Active site molecular modelling of xanthine oxidase inhibitors with antiinflammatory activity. ACTA ACUST UNITED AC 1985. [DOI: 10.1016/0263-7855(85)80026-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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17
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Rosemeyer H, Seela F. Methylated 7-deazahypoxanthines as regiochemical probes of xanthine oxidase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1983; 134:513-5. [PMID: 6688395 DOI: 10.1111/j.1432-1033.1983.tb07596.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
7-Deazahypoxanthine was found to be oxidised by cow's milk xanthine oxidase exclusively at carbon 2. The resulting 7-deazaxanthine is a strong inhibitor of the enzymatic reaction. This offers a possibility for determining the structural requirements of ligand binding separately for the first step. All the monomethyl isomers of 7-deazahypoxanthine were tested as probes by measuring their Km, Ki and V values. While the N-3-methyl and C-7-methyl isomers are still processed, the N-9-methyl and 6-O-methyl isomers are bound as inhibitors to the active site. The N-1-methyl compound is neither an inhibitor nor a substrate. This demonstrates that HN(1) and O = C(6) are essential for the binding. Replacement of O = C(6) by S = C(6) changes the substrate into a strong inhibitor (Ki = 9 microM), implying that the electron transfer to the enzyme is hindered. Methylation of the thioxo group (S =) reduces the inhibition significantly. In contrast to 7-deazahypoxanthine, 2-thioxo-7-deazaxanthine is an activator at concentrations below 87 microM and a partial competitive inhibitor above this concentration, which implies the presence of a second binding site.
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Bunting JW, Gunasekara A. An important enzyme-substrate binding interaction for xanthine oxidase. ACTA ACUST UNITED AC 1982. [DOI: 10.1016/0167-4838(82)90066-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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19
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Auscher C, Amory N, van der Kemp P, Delbarre F. Xanthine oxidase activity in human intestines. Histochemical and radiochemical study. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1980; 122B:197-201. [PMID: 583538 DOI: 10.1007/978-1-4684-8559-2_33] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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20
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Entsch B, Parker CW, Letham DS, Summons RE. Preparation and characterization, using high-performance liquid chromatography, of an enzyme forming glucosides of cytokinins. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 570:124-39. [PMID: 486500 DOI: 10.1016/0005-2744(79)90207-9] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Cytokinins can occur naturally as glycosides with beta-D-glucose as the sugar substituent. From radish (Raphanus sativus) cotyledons, an enzyme has been partly purified which synthesizes the 7-glucopyranoside of zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine], a compound known to occur in this species. High-performance reverse-phase liquid chromatography was uniquely useful as the analytical procedure for quantitative study of the minute amounts of enzyme available. The enzyme uses UDPglucose as the source of the sugar residue. A large number of derivatives of purine are glucosylated, but adenine derivatives with an alkyl side chain at least three carbon atoms in length at position N6 are preferentially glucosylated. This corresponds to the structural features required for high cytokinin activity. The 7-glucoside of zeatin is known to be very weakly active in cytokinin bioassays. Hence, this enzyme, and others catalyzing the same reaction, have a role in the regulation of cytokinin activity.
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Bergmann F, Frank A, Govrin H. Behavior of N-methylated allopurinols and related 4-thioxopyrazolo [3,4-d]pyrimidines towards bovine milk xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 570:215-20. [PMID: 486504 DOI: 10.1016/0005-2744(79)90217-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
1. All available N-mono- and N,N'-dimethylallopurinols and the corresponding 4-thioxo derivatives have been tested as substrates or inhibitors of bovine milk xanthine oxidase (xanthine: oxygen oxidoreductase, EC 1.2.3.2). 2. None of the compounds tested revealed any inhibitory activity towards the enzyme. 3. All compounds were resistant to enzymic oxidation, with the exception of 7-methylallopurinol and its 4-thioxo analog. Both these compounds were attacked at position 6. 7-Methylallopurinol was oxidised nearly ten times faster than the isomeric 3-methylhypoxanthine. 4. These observations can be explained by assuming that for attack at C-6, the enzyme must bind both to N-1 and N-2 in the pyrazole ring and causes tautomerisation, which places a double bond at position 5,6 in the pyrimidine ring. This activation process resembles the activation of hypoxanthine.
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Breter HJ, Maidhof A, Zahn RK. The quantitative determination of metabolites of 6-mercaptopurine in biological materials. III. The determination of 14C-labeled 6-thiopurines in L5178Y cell extracts using high-pressure liquid cation-exchange chromatography. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 518:205-15. [PMID: 418811 DOI: 10.1016/0005-2787(78)90178-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A method is presented for the separation of 6-thiopurine bases and ribonucleosides, of sulphate anions and of common purine bases and oxidized purines by means of high-pressure liquid cation-exchange chromatography using a 0.18 X 100 cm column, filled with Beckman M71 resin, and eluted with 0.4M ammonium formate, pH 4.6, at a linear flow velocity of 5.2 cm/min at 50 degrees C. The method has been applied to the separation and quantitative determination of 14C-labeled 6-mercaptopurine metabolites in HClO4 extracts of L5178Y murine lymphoma cells. Distribution patterns of 14C radioactivity within the cells after a 24 h incubation period with (8-14C)-labeled 6-mercaptopurine have been established. The indentification of 6-mercaptopurine metabolites, such as 6-thioxanthosine ribonucleotide, 6-thioinosinic acid, 6-thioguanylic acid, 6-methylthioinosinic acid, and 6-thiouric acid, after the digestion of the extracts with alkaline phosphatase has been confirmed using the behaviour of each compound in enzymatic peak-shifting analyses with purine nucleoside phosphorylase and the corresponding elution volumes of 6-thiopurine bases and ribonucleosides as proofs. According to the specific radioactivity of the (8-14C)-labeled 6-mercaptopurine batch, the amounts of the various 6-mercaptopurine metabolites in about 6% of the total HClO4 extract of 1.6 . 10(8) labeled cells have quantitatively been determined as 1--130 pmol. The intracellular concentration of 6-thiopurines was determined at 1.4 . 10(-5)mol/1.
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Bergmann F, Levene L, Govrin H. Oxidation of hypoxanthines, bearing 8-aryl or 8-pyridyl substituents, by bovine milk xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 484:275-89. [PMID: 20959 DOI: 10.1016/0005-2744(77)90084-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
1. Hypoxanthines, bearing at position 8 aryl or pyridyl substituents, are converted by bovine milk xanthine oxidase (xanthine: oxygen oxidoreductase, EC 1.2.3.2) into the corresponding xanthines at low rates. Oxidation is accelerated considerably when the 8-pyridyl substituents are quaternised. 2. In the enzymic oxidation of quaternary 8-pyridylhypoxanthines a lag phase precedes the attainment of a constant, maximal reaction rate. It is assumed that the delay is due to a relatively slow conformational change in the active enzymic center. 3. In 8-(3'-N-methylpyridinio)xanthine betaine, also the pyridinium moiety is attacked at high pH (9-11) to yield an N-methyl-2-pyridone. The analogous pyridone is the only oxidation product of 1-methyl-8-(3'-N-methylpyridinio)-hypoxanthine betaine, which is not attacked in the pyrimidine ring. 4. The cationic substrates are attracted to the enzyme by an anionic group, which probably forms an ion pair with a protonated amino group in or near the active center.
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Breter HJ. The quantitative determination of metabolites of 6-mercaptopurine in biological materials. I. A separation method for purine and 6-thiopurine bases and nucleosides using high-pressure liquid cation-exchange chromatography. Anal Biochem 1977; 80:9-19. [PMID: 883647 DOI: 10.1016/0003-2697(77)90620-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Bergmann F, Levene L. Enzymic oxidation of 3-hydroxyxanthine to 3-hydroxyuric acid. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 481:359-63. [PMID: 15604 DOI: 10.1016/0005-2744(77)90269-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
1. Bovine milk xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) oxidises 3-hydroxyxanthine slowly to 3-hydroxyuric acid; the 1-methyl derivative of 3-hydroxyxanthine is attacked about twice as fast. 2. The pH optimum for the reaction of 2-hydroxyxanthine is near 5, i.e. the neutral form of this substrate is attacked much faster than the anion. Probably in the "active" form of the latter, the negative charge is located mainly in the imidazole ring, thus inhibiting nucleophilic attack at C-8.
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Bergmann F, Levene L, Tamir I, Rahat M. Oxidation of methyl derivatives of pteridin-4-one, lumazine and related pteridines by bovine milk xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 480:21-38. [PMID: 12825 DOI: 10.1016/0005-2744(77)90317-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
1. Pteridin-4-ones, methylated at nitrogen or carbon, N-methylated lumazines and related oxopteridines were studied as substrates of a highly purified bovine milk xanthine oxidase (xanthine : oxygen oxidoreductase, EC 1.2.3.2). 2. The enzyme can oxidise at high rates both uncharged and anionic substrates. Variation of enzymic activity with pH is mainly due to pH-dependent changes in the active enzymic center. 3. Milk xanthine oxidases at different stages of purification convert pteridin-4-one into the 4,7-dione (compound 13 in this article). 4. Methylation at C-6 in the pyrazine moiety enhances enzymic attack at C-2 in the pyrimidine ring. N-Methylation may increase or reduce rates of oxidation. 5. For oxidation at C-2, the most favorable form of the substrate bears a double bond at C(2) = N(3). Attack at C-7 is enhanced strongly in structures bearing a double bond at C(6) = C(7). 6. In general, pteridines react with xanthine oxidase as non-hydrated molecules. However, oxidation of 8-methyllumazine at C-7 may take place by dehydrogenation of the 7-CHOH group of the covalently hydrated molecule.
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Bergmann F, Levene L, Govrin H, Frank A. Influence of 8-substitutes on the oxidation of hypoxanthine and 6-thioxopurine by bovine milk xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 480:39-46. [PMID: 12828 DOI: 10.1016/0005-2744(77)90318-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
1. The influence of 8-substituents was studied on the rate of oxidation of hypoxanthine and 6-thioxopurine by bovine milk xanthine oxidase (EC 1.2.3.2). 2. An 8-methyl group does not alter the rate of oxidation of hypoxanthine materially, but an 8-phenyl substituent reduces it markedly. This is ascribed to inhibition of the tautomerisation process, responsible for substrate activation, prior to oxidation. 3. In contrast, the 8-phenyl group in 3-methyl-8-phenylhypoxanthine enhances the rate, presumably by binding to a hydrophobic site near the enzymaic center. 4. An 8-phenyl group in 6-thioxopurine markedly increases the rate of enzymaic oxidation. Probably the aromatic substituent diverts anion formation to the imidazole ring. In contrast, ionisation of 8-methyl-6-thioxopurine involves the pyrimidine moiety, thus rendering enzymic attack at position 2 more difficult.
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