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)

Purified glutathione S-transferase from rat liver cytosol are irreversibly inhibited by the glutathione conjugate of tetrachloro-1,4-benzoquinone, 2-S-glutathionyl-3,5,6-trichloro-1,4-benzoquinone. The inhibition is due to covalent binding in or near the active site, resulting in modification of a single amino acid residue/subunit, presumably a cysteine residue. The amount of inhibition is related to the molar ratio of the inhibitor and the enzyme and is independent of the enzyme concentration. A 70-80% inhibition is obtained on incubating the enzyme with a 5-fold molar excess of the conjugate. Complete 100% inhibition is never reached. The derivative bound to the enzyme still possesses a quinone structure and is able to react with thiol-containing compounds. Reduction of the enzyme-bound quinone abolishes its reactivity but does not decrease the inhibition. At 0 degrees C, the glutathione conjugate of tetrachloro-1,4-benzoquinone inhibits the glutathione S-transferases at a much higher rate than the corresponding beta-mercaptoethanol conjugate, indicating a distinct targetting effect of the glutathione moiety. However, the parent compound, tetrachloro-1,4-benzoquinone, also has a considerable affinity for the enzymes. Although it does not react as fast as the glutathione conjugate, it reacts with the same amino acid residue. Protection from inhibition by the substrate analog S-hexylglutathione also indicates an active site-directed modification. Small but significant differences exist between the different rat liver transferase isoenzymes; using a 20-fold molar excess the inhibition ranges from 78 to 98% for the conjugate, and from 72 to 93% for the quinone, with isoenzyme 1-1 being the most and isoenzyme 2-2 the least inhibited forms.
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PMID:Active site-directed irreversible inhibition of glutathione S-transferases by the glutathione conjugate of tetrachloro-1,4-benzoquinone. 341 44

Periportal and perivenous hepatocytes were isolated by the digitonin-collagenase perfusion technique. The activity of the cytosolic glutathione S-transferase was higher in perivenous cells, but the cytosolic glutathione reductase and the microsomal glutathione S-transferase activities were evenly distributed. In contrast, both the Se-dependent and the microsomal Se-independent glutathione peroxidase activity and the glucose-6-phosphate dehydrogenase activity was much lower in perivenous hepatocytes, suggesting that these cells have a lowered detoxification capacity, which may contribute to their greater susceptibility to damage by xenobiotics. The mechanism of the ethanol-induced GSH depletion in vivo was studied by incubating conventionally isolated hepatocytes. In the absence of glutathione precursors, ethanol (80 mM) did not influence the GSH content, despite accumulation of acetaldehyde (10-100 MicroM). L-Methionine or L-cysteine stimulated GSH replenishment to in vivo rates. Ethanol oxidation resulted in acetaldehyde accumulation, but did not inhibit GSH replenishment from L-methionine and even stimulated that from L-cysteine. This seems to exclude conjugation of GSH with acetaldehyde as a mechanism by which ethanol suppresses GSH levels in vivo.
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PMID:Glutathione metabolism in isolated rat hepatocytes: acinar heterogeneity of detoxifying enzymes and effects of ethanol. 342 86

Chronic ethanol feeding increases hepatic turnover and sinusoidal efflux of glutathione in rats. The present study was performed to determine whether the observed increase in glutathione efflux was due to increased extrahepatic requirements for glutathione. The concentration and disposition of plasma glutathione were determined in rats fed liquid diets containing 36% of calories as ethanol or pair-fed an isocaloric mixture with carbohydrate replacing ethanol calories for 5 to 8 weeks. The half-life and plasma clearance of [35S]glutathione were found to be similar in ethanol-fed and control rats and in rats withdrawn 24 hr from ethanol. Uptakes of the sulfur moiety of [35S]glutathione by kidney, jejunal mucosa, liver, lung, spleen, muscle and heart were also unchanged by ethanol feeding. The plasma glutathione concentration was significantly higher in ethanol-withdrawn rats 22.30 +/- 3.06 nmoles per ml (p less than 0.05) compared to pair-fed controls (13.51 +/- 2.04), while rats continuing to drink ethanol had intermediate levels (16.96 +/- 2.22). Plasma cysteine levels were slightly, but not significantly, higher in ethanol-fed rats. These findings suggest that increased sinusoidal efflux of glutathione in ethanol-fed rats is due to a direct effect of ethanol on hepatic glutathione transport and not due to an alteration in extrahepatic disposition of glutathione. In order to characterize further the effects of ethanol feeding on glutathione-dependent detoxification, activities of glutathione S-transferase, glutathione reductase and gamma-glutamyltransferase were determined.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of ethanol feeding and withdrawal on plasma glutathione elimination in the rat. 357 Jan 60

Toxic effects of SO2 and sulfite such as bronchitis and bronchoconstriction have been well documented. SO2 has also been suggested to potentiate carcinogenic effects of PAH. However, the molecular basis of these toxic effects is unclear. We have examined the covalent reaction of SO2 and sulfite with cellular proteinacious and nonproteinaceous sulfhydryl compounds using rat liver, and lung and human lung derived A549 cells. Reactions of sulfite and protein in rat and human lung cells reveals at least three proteins with sulfite-reactive disulfide bonds. Besides fibronectin and serum albumin, which had been reported to contain sulfonated products following exposure to sulfite, we have found one other protein with sulfite-binding capabilities. Since the integrity of disulfide bonds is crucial to the tertiary structure and thus protein function, the disruption of protein structure by sulfitolysis may result in altered cellular activities leading to biochemical lesions. Using carefully controlled conditions, reproducible GSH contents can be found in cultured cells and used as an experimental basis for studying alterations in the GSH and GSSG content of cells. Sulfitolysis of GSSG results in the formation of GSSO3H in A549 cells, and possibly in the lung. GSSO3H can be reduced enzymatically by GSSG reductase. However, the Km of GSSO3H is high compared to that of GSSG, suggesting the existence of a transient concentration of GSSO3H once it is formed. Cysteine S-sulfonate is, however, not reduced by cytosolic extracts in the presence of NADPH and would have to be eliminated from the cell by other means. GSSO3H is a strong competitive inhibitor of GST in rat liver and lung and A549 cells, using 1-chloro-2,4-dinitrobenzene as a substrate. It also inhibits the formation of GSH conjugates of BP 4,5-oxide, anti and syn BPDE, but to a lesser extent. These results suggest that SO2 may affect the detoxification of xenobiotic compounds by inhibiting, via formation of GSSO3H, the enzymatic conjugation of GSH and reactive electrophiles. Since GSH conjugation represents the major pathway of elimination of BP epoxides in the lung, our results offer a possible explanation for the cocarcinogenicity of SO2 with PAHs. These data suggest that the sulfitolysis reaction of sulfite is the common reaction mechanism mediating the underlying biochemical reactions leading to both the toxic and cocarcinogenic properties of SO2. Quantitation of sulfitolysis products and their interaction with cellular processes should provide a coherent scheme relating SO2 and sulfite toxicity among animal species and humans.
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PMID:Covalent reactions in the toxicity of SO2 and sulfite. 376 76

After rats were injected with the reduced glutathione (GSH) depletor phorone (diisopropylidene acetone, 250 mg/kg, i.p.), there was a significant increase in microsomal glutathione S-transferase activity in the liver. The maximum activity was observed 24 hr after injection and was about 2-fold that of the control activity. Diethylmaleate (500 mg/kg, i.p.) had the same effect. Twenty-four hours after phorone injection (250 mg/kg, i.p.), the concentrations of GSH and oxidized glutathione (GSSG) in the liver were increased about 2-fold. Under the same conditions, the level of mixed disulfides with microsomal proteins (GSS-protein) was also increased. Further, the activity of microsomal glutathione S-transferases was increased by the in vitro addition of disulfide compounds such as GSSG, cystine and homocystine, and the activity increased by GSSG was reduced to control levels by incubating with the corresponding sulfhydryl compounds such as GSH, cysteine and homocysteine respectively. Thus, microsomal glutathione S-transferase activity appears to be regulated by the formation and/or cleavage of a mixed disulfide bond between the sulfhydryl group present in the enzyme and GSSG. Therefore, the increase of microsomal glutathione S-transferase activity after phorone injection may be due to the formation of a mixed disulfide bond between the sulfhydryl group in the enzyme and GSSG.
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PMID:Possible regulation mechanism of microsomal glutathione S-transferase activity in rat liver. 394 80

The effect of chloroform treatment on the hepatic glutathione S-transferases was studied in phenobarbital-treated rats. The apparent isozymic composition of glutathione S-transferases in hepatic cytosol was changed after chloroform treatment. Glutathione S-transferases AA, A, B, C, and D + E were observed in hepatic cytosol from untreated rats; in contrast, the catalytic activity associated with basic glutathione S-transferases, such as AA, A, B, and C, decreased with time after chloroform treatment. Glutathione S-transferase B was not detectable 2 hr after chloroform treatment, and glutathione S-transferases AA and C were scarcely detectable after 5 hr. Twenty-four hours after chloroform treatment, glutathione S-transferases A and C were clearly detectable as was D + E and a small amount of B. Hepatic cytosolic glutathione S-transferase activity was decreased by chloroform treatment, and reached a minimum at 5 hr after treatment. Corresponding to the decrease of hepatic cytosol glutathione S-transferase activity, serum glutathione S-transferase activity was elevated maximally 5 hr after chloroform treatment and returned to almost normal by 24 hr. Treatment of rats with SKF 525-A or cysteine inhibited the chloroform-induced elevation of serum glutathione S-transferase activity. The chromatographic properties of the glutathione S-transferases present in serum were similar to glutathione S-transferase D + E. Furthermore, after incubation of partially purified cytosolic glutathione S-transferases with chloroform in the presence of hepatic microsomes and NADPH, only transferase D + E was detected. The addition of bilirubin to partially purified cytosolic glutathione S-transferase decreased the basic character of glutathione S-transferases B and C. In conclusion, chloroform caused a release of hepatic cytosolic glutathione S-transferases into serum. Both the active metabolite of chloroform, which was produced by the microsomal cytochrome P-450 system, and bilirubin, which was increased by chloroform treatment, played roles in altering the properties of the glutathione S-transferases.
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PMID:Chloroform-induced alteration of glutathione S-transferase activity. 396 26

Incubations with goat lung and liver microsomes were conducted to trap with exogenous glutathione (GSH) the electrophilic intermediate produced via cytochrome P-450-dependent metabolic activation of 3-methylindole (3MI). Microsomal incubation mixtures with [14C]3MI, a NADPH-generating system, and [3H]GSH produced a dual-labeled adduct which was isolated by reverse-phase high-performance liquid chromatography. Reactive 3MI intermediates were also trapped with cysteine. Adduct formation increased in proportion to the concentration of either thiol. Covalent binding of activated 3MI metabolites to microsomal protein was inversely related to adduct production. There were both qualitative and quantitative differences in the formation of GSH adducts by lung and liver microsomes. In the presence of 2 mM GSH, the adduct was produced at a rate of 1.8 nmol/mg protein/min by lung microsomes but only at 0.1 nmol/mg protein/min by hepatic microsomes. The addition of cytosolic fractions containing glutathione S-transferase activity increased GSH adduct formation by approximately 30%. These results support the view that electrophilic 3MI intermediates are trapped by conjugation with GSH, and that organ-selective toxicity is primarily due to much faster rates of cytochrome P-450 oxidation of 3MI in the lung than in the liver.
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PMID:Glutathione adduct formation with microsomally activated metabolites of the pulmonary alkylating and cytotoxic agent, 3-methylindole. 404 23

Modulation of cholesterol 7 alpha-hydroxylase activity was studied in a purified, reconstituted system from rat liver microsomes. Cysteine, dithiothreitol, reduced glutathione, and thioredoxin activated the system whereas glutathione disulfide inactivated it. A protein, which stimulated cholesterol 7 alpha-hydroxylase activity in the presence of glutathione or thioredoxin, was purified to apparent homogeneity from rat liver cytosol. It has a minimum Mr of 25,000. The protein had no effect on 12 alpha-hydroxylation of 7 alpha-hydroxy-4-cholesten-3-one or 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. The cholesterol 7 alpha-hydroxylase stimulatory protein could not be replaced by the thioltransferase-dependent disulfide-reducing system nor by glutathione S-transferase A, B, or C. Neither ATP and MgCl2 nor sodium fluoride had any effect on the activity of the cholesterol 7 alpha-hydroxylase stimulatory protein. The results show that purified cholesterol 7 alpha-hydroxylase can be regulated by a mechanism involving disulfide bonds in the cytochrome P-450 molecule.
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PMID:Regulation of hydroxylations in biosynthesis of bile acids. Isolation of a protein from rat liver cytosol stimulating reconstituted cholesterol 7 alpha-hydroxylase activity. 658 30

The S-methylated derivatives of N-acetylpenicillamine, thiola and cysteine as well as methyl iodide decreased biliary excretion of methyl mercury markedly. Excretion of sulfhydryl in bile was not influenced by S-methyl-cysteine, S-methylthiola, S-methyl-N-acetylpenicillamine or a low dose of methyliodide (0.5 mmol/kg body weight). This seems to indicate that coupling of methyl mercury to glutathione in the liver before biliary excretion is a glutathione S-transferase dependent reaction. It also indicates that the methylthiols tested, or metabolites of these compounds are likely to be inhibitors of S-transferase. The effect of S-methylcysteine and low doses of methyl iodide probably reflects glutathione S-transferase inhibition as both compounds are metabolized to the S-transferase inhibitor S-methylglutathione in the liver. A higher dose of methyl iodide (1 mmol/kg body weight) seems to deplete the liver of reduced glutathione through S-methylation as illustrated by decreased biliary excretion of sulfhydryl. S-methylthiola and S-methyl-N-acetylpenicillamine are metabolized in the liver to unknown components which are excreted in bile. Whether S-methylthiola and S-methyl-N-acetylpenicillamine are inhibitors of S-transferase themselves or cause inhibition through metabolites cannot be stated from the present investigation.
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PMID:The mechanism of biliary excretion of methyl mercury: studies with methylthiols. 662 83

Conditions have been examined for the use of o-dinitrobenzene as a substrate for colorimetric assay of glutathione S-transferases. Activities can be determined by measuring nitrite released enzymatically from the substrate using a diazo-coupling method with N-(1-naphthyl)ethylenediamine dihydrochloride and sulfanilamide. The assay can be done in the presence of large amounts of reduced glutathione (GSH), cysteine, and protein, and is capable of quantitating the enzyme activity in about 30 micrograms (wet weight) of monkey liver, corresponding to 0.1 microgram of purified glutathione S-transferase from the same source. This method is suitable for assaying simultaneously a large number of samples with reasonable sensitivity and speed.
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PMID:A colorimetric assay of glutathione S-transferases using o-dinitrobenzene as a substrate. 665 79


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