Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.5.1.18 (glutathione S-transferase)
22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Each of the four stereoisomers of trans-3,4-dihydroxy 1,2-epoxy 1,2,3,4-tetrahydrobenzo[c]phenanthrene [(+)- and (-)-anti-BPhDE and (+)- and (-)-syn-BPhDE] has been incubated with the human glutathione transferase (GST) isoenzymes GST A1-1, GST M1-1 and GST P1-1, representing class alpha, mu and pi respectively, and glutathione (GSH). The conjugates formed were analyzed by HPLC and the results demonstrate that all GST isoenzymes catalyze the formation of GSH conjugates of all BPhDE isomers. However, a marked variation in catalytic efficiencies was observed (0.122-1.28/mM/s). These values are considerably lower than those previously estimated for the bay-region diol epoxides of benzo[a]pyrene (B[a]P) and human GSTs. The (+)-syn and (-)-anti-BPhDE (1R,2S-epoxide absolute configuration) were in general better substrates than the corresponding 1S,2R-epoxides. In accordance with previous observations with the diolepoxides of B[a]P, GST P1-1 was highly selective towards the BPhDE isomer with 4R,3S-diol 2S,1R-epoxide absolute configuration, i.e. (-)-anti-BPhDE, whereas GST A1-1 and M1-1 preferentially catalyzed the conjugation of (+)-syn-BPhDE (4R,3S-diol 2R,1S-epoxide absolute configuration). Overall, the most active isoenzyme was GST A1-1. Analysis by NMR spectroscopy of the GSH conjugates of BPhDE demonstrate that the reaction with GSH generally takes place by trans-addition of the thiol group at the benzylic C-1 carbon. The low catalytic efficiencies of human GSTs with BPhDE as compared to diolepoxides of B[a]P may be explained in part by the more crowded bay-region and substantially lower chemical reactivity (e.g. delta Edeloc/beta) of the former compounds.
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PMID:Glutathione conjugation of trans-3,4-dihydroxy 1,2-epoxy 1,2,3,4-tetrahydrobenzo[c]phenanthrene isomers by human glutathione transferases. 139 38

Benastatins A and B, new inhibitors of glutathione S-transferase, have been isolated from the culture broth of Streptomyces sp. MI384-DF12. By X-ray crystallography, benastatin A was determined to be 8,13-dihydro-1,7,9,11-tetrahydroxy-13-dimethyl-8-oxo-3-pentyl- benzo[a]naphthacene-2-carboxylic acid. The structure of benastatin B was elucidated by NMR studies.
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PMID:Benastatins A and B, new inhibitors of glutathione S-transferase, produced by Streptomyces sp. MI384-DF12. II. Structure determination of benastatins A and B. 142 23

The substrate-binding site of a human muscle class mu glutathione transferase has been characterized using high-resolution nuclear magnetic resonance spectroscopy. Isotopic labeling has been used to simplify one-dimensional proton NMR spectra of the Tyr and His residues in the enzyme and two-dimensional carbon-proton spectra of the Ala and Met residues in the enzyme. The resonance lines from 8 of the 12 Tyr residues have been assigned using site-directed mutagenesis. Replacement of Tyr7 with Phe reduced the activity of the enzyme 100-fold. The proximity of His, Tyr, Ala, and Met residues to the active site has been determined using a nitroxide-labeled substrate analogue. This substrate analogue binds with high affinity (Keq = 10(6) M-1) to the enzyme and is a competitive inhibitor. None of the His residues are within 17 A of the active site. Three of the assigned Tyr residues are greater than 17 A from the active site. Quantitative measurement of paramagnetic line broadening of five additional Tyr residues places them within 13-17 A from the active site. Broadening of the Ala and Met resonance lines by the spin-labeled substrate indicates that three Ala residues are 9-16 A from the nitroxide, three Met residues are less than 9 A from the nitroxide, and two Met residues are 9-16 A from the nitroxide.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mapping the substrate-binding site of a human class mu glutathione transferase using nuclear magnetic resonance spectroscopy. 155 Aug 17

We have previously shown that 2-hydroxamino-1-methyl-6-phenylimidazo[4,5-b]pyridine(2-h ydroxamino-PhIP) is the principal metabolite leading to mutations in Salmonella typhimurium TA98 and DNA damage in mammalian cells. In rat hepatocytes this metabolite can be further conjugated to 2-(N-beta-D-glucuronopyranosyl (hydroxamino)-1-methyl-6-phenylimidazo[4, 5-b]pyridine[N(OH)-gluc-PhIP]. Its rate of formation was increased in hepatocytes from polychlorinated biphenyl (PCB)-pretreated animals. This metabolite is the main metabolite of PhIP in bile and it is hydrolyzed both by human and rat intestinal bacteria. Smaller amounts are excreted into urine. The evidence for the proposed structure is based on 1H- and 13C-NMR, beta-glucuronidase-lability giving 2-hydroxamino-PhIP upon hydrolysis and on the results obtained by using biochemical enzyme inhibitors. N(OH)-gluc-PhIP may be important for genotoxic lesions and tumors of 2-amino-1methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) in extrahepatic tissue. In hepatocytes and bile from PCB-pretreated rats a PhIP-glutathione conjugate, 2-glutathionyl-1-methyl-6-phenylimidazo[4,5-b]pyridine (GSH-PhIP) was also found. The evidence for the proposed structure is based on 1H-NMR and high-resolution mass spectrometry. The metabolite can also be produced by a direct nucleophilic substitution of the nitro group in 2-nitro-PhIP by glutathione (GSH) in vitro. The metabolite did not form from 2-hydroxamino-PhIP and GSH either directly or in the presence of glutathione S-transferase. The formation of GSH-PhIP in rat liver and isolated cells only at a high rate of 2-hydroxamino-PhIP formation (PCB-treated animals) indicates that 2-nitro-PhIP may be formed in the liver during such N-oxidation of PhIP.
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PMID:Formation of a glutathione conjugate and a semistable transportable glucuronide conjugate of N2-oxidized species of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in rat liver. 174 23

To test the proposition that a histidine residue is essential in the catalytic mechanism of glutathione S-transferase, rat liver isoenzyme 3-3 specifically labeled with [ring-2-13C]histidine was prepared. The 13C NMR spectrum of the labeled enzyme revealed four resonances corresponding to the 4 histidine residues in the mu gene class type 3 subunit. Titration of the four resonances in the range of pH 4-9 both in the presence and absence of glutathione gave pK alpha values of much less than 4, 5.2, 7.1, and 7.8 for the four side chains that were identified by site-specific mutagenesis as His14, His83, His84, and His167, respectively. The magnetic resonance properties and titration behavior of His14 suggest that this residue is buried in a hydrophobic environment. Conservative replacement of each histidine with asparagine results in mutant enzymes that have catalytic properties very close to the native protein as assessed with three different substrates, 1-chloro-2,4-dinitrobenzene, 4-phenyl-3-buten-2-one, and phenanthrene 9,10-oxide. The results indicate clearly that none of the histidine residues of isoenzyme 3-3 is essential for stabilization of the bound glutathione thiolate or for any other aspect of catalysis.
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PMID:Are the histidine residues of glutathione S-transferase important in catalysis? An assessment by 13C NMR spectroscopy and site-specific mutagenesis. 191 58

Two examples are described of the use of NMR spectroscopy to study the modification of DNA structure by carcinogens. The reaction of ethylene dibromide involves initial conjugation with glutathione, catalysed by glutathione S-transferase. Reaction of this adduct with DNA occurs at N7 of guanine. Through the use of stereospecifically 1,2-dideuteriated ethylene dibromide, the mechanism of reaction has been shown to involve an odd number, i.e. three, of SN2 inversions. Correlation spectra (COSY) were employed to analyse reaction stereochemistry. The relative configuration of the deuterium atoms in the products was initially assigned by 1H nuclear Overhauser effect (NOE) difference spectra and then confirmed by an independent synthesis of stereospecifically dideuteriated glutathione-guanine adducts. The second example involves reaction of the epoxide of aflatoxin B1 with DNA to form covalent adducts at N7 of guanine. Adduct formation was found to enhance duplex stability. Chemical shift changes for aflatoxin protons in the covalent adduct when compared with those for aflatoxin B1 non-covalently associated with DNA suggest that covalently linked aflatoxin is intercalated. NOEs confirm that the aflatoxin moiety is intercalated and show that it is on the 5' side of the guanine. This geometry leads to d(ATCGAT)2 forming an adduct in which only one chain has been modified by aflatoxin, while d(ATGCAT)2 forms a complex in which both chains have been modified.
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PMID:NMR-studies of carcinogen reactions with DNA: ethylene dibromide and aflatoxin B1. 212 14

Using a partially purified 12-lipoxygenase from porcine leukocytes, (5Z,8Z,10E,14Z)-12-hydroperoxy-5,8,10,14-icosate traenoic acid was synthesized from arachidonic acid with a yield of over 35%. The absolute configuration of C-12 was determined as S by chiral-phase column chromatography. It was chemically converted to at least three epoxides with the conjugated triene structure. Two were identified by proton NMR and mass spectrometry to be (5Z,7E,9E,14Z)-(11S,12S)-11,12-oxido-5,7,9,14-ic osatetraenoic acid (11,12-leukotriene A4) and (5Z,7Z,9E,14Z)-(11S,12S)-11,12-oxido-5,7,9,14-ic osatetraenoic acid (7-cis-11,12-leukotriene A4). 11,12-Leukotriene A4 underwent acid hydrolysis to yield two diastereomers of (6E,8E,10E,14Z)-(12S)-5,12-dihydroxy-6,8,10,14-i cosatetraenoic acid and two isomers of (14Z)-(12S)-11,12-dihydroxy-5,7,9,14-icosatetraenoic acid. Upon incubation with rat liver glutathione S-transferase, 11,12-leukotriene A4 was converted to 11,12-leukotriene C4, a spasmogenic compound.
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PMID:Synthesis and structural identification of four dihydroxy acids and 11,12-leukotriene C4 derived from 11,12-leukotriene A4. 316 22

Six different 1,2-epoxycycloalkanes, whose rings were constituted of 5 to 12 carbon atoms, were tested as possible inhibitors of epoxide-metabolizing enzymes and substrates for the microsomal and cytosolic epoxide hydrolases (mEH, cEH) in mouse liver. The geometric configurations and the relative steric hindrances of these epoxides were estimated from their ease of hydrolysis in acidic conditions to the corresponding diols, their abilities to react with nitrobenzylpyridine, and the chemical shifts of the groups associated with the oxirane rings measured by proton and 13C-NMR. The cyclopentene, -hexene, -heptene, -octene and -decene oxides adopted mainly a cis-configuration. By contrast, cyclododecene oxide presented a trans-configuration. Steric hindrance increased with the size of the ring and was particularly strong when cyclooctene, -decene and -dodecene oxides were considered. With the exception of cyclohexene oxide, all the compounds were weak inhibitors of EH and glutathione S-transferase (GST) activities. Cyclohexene oxide exhibited a selective inhibition of the mEH with an I50 of 4.0.10(-6) M. As the size of the ring increased, inhibitory potency was gradually lost. The cEH and the GST activities were less sensitive to the inhibitory effects of these epoxides (I50, 1 mM or above). A marked difference between the substrate selectivities of mEH and cEH for these epoxides was observed. The mEH hydrated all of the cyclic epoxides, although some of them at a very low rate; the best substrate was the cycloheptene oxide (2.3 nmol/min/mg protein). On the other hand, cyclodecene oxide was a substrate of cEH, but no diol formation was detected when cyclopentene, -hexene and -dodecene oxides were incubated with cytosolic enzyme.
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PMID:1,2-Epoxycycloalkanes: substrates and inhibitors of microsomal and cytosolic epoxide hydrolases in mouse liver. 339 52

The reaction of 1,2-dibromoethane and glutathione with DNA in the presence of glutathione S-transferase results in the formation of a single major DNA adduct, which can be released by thermal hydrolysis at neutral pH and separated by octadecylsilyl and propylamino high-performance liquid chromatography. The same DNA adduct is the only major one formed in livers of rats treated with 1,2-dibromo[1,2-14C]ethane. The DNA adduct was identified as S-[2-(N7-guanyl)ethyl]glutathione: (1) The chromatographic behavior was altered by treatment with gamma-glutamyl transpeptidase or Streptomyces griseus protease. (2) The molecular ions observed in positive and negative mode fast atom bombardment mass spectrometry were those expected for the structure when either glycerol or a mixture of dithiothreitol and dithioerythritol was used as the bombardment matrix. (3) The two-dimensional 1H NMR correlated spectroscopy spectrum of the DNA adduct was compared to the spectra of glutathione, oxidized glutathione, and N7-methylguanine and found to be consistent with the assigned structure. No evidence for in vitro or in vivo opening of the guanyl imidazole ring was observed under these conditions. The structure of the adduct supports a pathway involving enzyme-catalyzed conjugation of 1,2-dibromoethane with glutathione, non-enzymatic dehydrohalogenation of the resulting half-mustard to form a cyclic episulfonium ion, and attack of the N7 nitrogen of DNA guanine on the episulfonium ion to generate this major DNA adduct, which may be related to the carcinogenicity of this chemical.
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PMID:S-[2-(N7-guanyl)ethyl]glutathione, the major DNA adduct formed from 1,2-dibromoethane. 370 41

1-Chloro-2,4-dinitrobenzene (CDNB) was used to conjugate glutathione (GSH) through the catalysis of lens glutathione S-transferase without the untoward oxidative damage to the lens mediated by GSH oxidants. A 2 hr treatment of the rat lens with 1 mM CDNB resulted in a nearly total depletion of lens GSH with neither formation of GSSG nor glutathione-protein mixed disulfides. Rubidium uptake was found to decrease linearly with the loss of GSH; nevertheless, ionic imbalance did not commence until more than 30% cation pump activity was lost. Glycolytic rate dropped following CDNB treatment, due probably to a decline in demand for ATP by the deactivated cation pump. 31P-NMR studies confirmed the irreversible loss of ATP. CDNB depletion of GSH resulted in a two-fold increase in 14CO2 production from [14C]-1-glucose. Whereas oxidative stress resulted in a six-fold increase in glucose utilization through the hexose monophosphate shunt (HMPS), CDNB-treated lenses showed no such stimulation. This indicated that the residual GSH following CDNB treatment was insufficient for the activation of the glutathione peroxidase-reductase-HMPS mechanism and raised the possibility that the increased glucose utilization might be due to mechanisms other than the HMPS. These results indicate an intimate correlation between the GSH content and major metabolic functions in the lens.
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PMID:Effect of glutathione deprivation on lens metabolism. 609 26


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