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)

The purpose of this work was to study the relative activities and stabilities of phase-I and phase-II drug metabolizing enzymes in incubation mixtures used in vitro genotoxicity testing in order to optimize the conditions of the assay, increase sensitivity and eliminate false negative results. Cytochrome P-450, NADPH-cytochrome P-450 (cytochrome c) reductase activity and various phase-I and phase-II enzyme activities of the drug-metabolizing system were determined in incubation mixtures used in liver microsomal assays. The behaviour of aminopyrine N-demethylase and p-nitroanisole O-demethylase activities as phase-I markers have been reported previously. Other activities measured were glutathione S-transferase, glutathione S-epoxide transferase and epoxide hydrase, and lipid peroxidation (LP) was determined. The experiments were carried out on liver S9 fractions derived from non-induced mice or mice induced with sodium phenobarbital (PB), and/or beta-naphthoflavone (beta-NF). The phase-II enzymes were much more stable (70-90% residual activity) than phase-I enzyme activities (35-60%) in all conditions tested. The residual cytochrome P-450 was approximately 70% stable and the remaining activity of NADPH-cytochrome c-reductase about 80%, indicating that this latter enzyme does not limit the rate of the monoxygenase system in these conditions. Phase-II enzymes were induced to a smaller extent (about 2 times) than in phase-I enzymes (5-6 times) by beta-NF + PB. NADPH-cytochrome c-reductase behaved as phase-II enzymes in this respect as well as for stability. LP was appreciably higher in non-induced than in induced animals. Treatment with the beta-NF + PB mixture, however, showed that induced enzymes were more stable than those obtained by simple induction with either beta-NF or PB alone. These results lead to the conclusion that prolonged incubation times in mutagenicity assays are unnecessary when considering the relative stabilities of the various phase-I and phase-II enzyme activities in the drug-metabolizing system.
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PMID:Stability of drug metabolizing enzymes during the incubation conditions of the liver microsomal assay with non-induced and induced mouse liver S-9 fractions. 311 50

[14C]Bromobenzene was incubated with NADPH-fortified liver homogenates from phenobarbital-treated rats, after which the glutathione S-transferases were isolated from the incubation mixture. Glutathione S-transferase activity, with 1-chloro-2,4-dinitrobenzene as the substrate, in the homogenate was unchanged after incubation with bromobenzene. Radioactivity derived from the [14C]bromobenzene remained associated with the cytosolic glutathione S-transferases after DE52 and Sephadex G-100 chromatography. Further purification of the cytosolic glutathione S-transferase by CM52 and hydroxylapatite chromatography showed that bromobenzene metabolites were bound to fractions containing glutathione S-transferase subunits 4, 5, and 1. The primary site of arylation appeared to be subunit 1, as indicated by autoradiography and hydroxylapatite chromatography. [14C]Bromobenzene metabolites were not bound to microsomal glutathione S-transferases. These data show that hepatic cytosolic glutathione S-transferases, especially glutathione S-transferases 4-4/5-5, 3-4, and 1-1 may act as trapping or scavenger proteins for reactive metabolites and that this effect is not associated with a loss of catalytic activity.
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PMID:Isozyme selective arylation of cytosolic glutathione S-transferase by [14C]bromobenzene metabolites. 334 81

Changes in lipid peroxide (thiobarbituric acid reactant) levels, in the content of non-protein sulfhydryls (NPSH) and total proteins, and in the activities of antioxidative protective enzymes were examined in the lungs of four animal species exposed to a mixture of NO2 and O3 for 2 weeks. Male mice, hamsters, rats and guinea pigs were used. Thiobarbituric acid (TBA) reactant levels were increased significantly in the lungs of mice and guinea pigs, but not in hamsters and rats. NPSH contents were increased markedly in hamsters, mice and rats, but not in guinea pigs. The activities of antioxidative protective enzymes also changed with the exposure. The most characteristic change was the significant increase in glutathione peroxidase (GPx-H2O2) activity in hamsters and rats - species which did not exhibit increases in their TBA reactant levels. The increase in this enzyme activity in mice was significant, but not very large. Furthermore, guinea pigs were genetically deficient in this enzyme, and the increase in glycolytic enzymes for regenerating NADPH was also lowest in guinea pigs. The glutathione S-transferase (GSH-Tase) activity in mice and guinea pigs was decreased by exposure to the combined gases. These results suggest that the increases in lipid peroxide levels in mice and guinea pigs may be due to a lesser ability to regenerate protective reducing substances, such as NPSH and NADPH, than that of hamsters and rats. Induction of protective enzyme activities on exposure to the combined gases was also poor in mice and guinea pigs.
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PMID:Biochemical effects of combined gases of nitrogen dioxide and ozone. II. Species differences in lipid peroxides and antioxidative protective enzymes in the lungs. 340 59

A major concern of contemporary medicine is the adverse effects resulting from the use of prescribed and over-the-counter pharmacologic agents. In many cases more than one drug is taken at the same time, which increases the risk of overloading the detoxification mechanisms. If the individual has poor nutritional status, the system becomes even more inefficient. The liver contains the most important of these detoxification systems: the cytochrome P-450-dependent mixed function oxidase (MFO) and several conjugation enzymes, e.g., sulfotransferase, glucuronyl transferase, and glutathione transferase, which convert lipophilic compounds to more water-soluble products to enhance their excretion. The balance of these reactions determines the rate of metabolism and clearance of xenobiotic agents, and regulates in part the degree of intracellular damage. Nutritional factors, including proteins, carbohydrates, fats, vitamins, and minerals, affect the efficiency of these reactions. Changes in intracellular metabolism can alter not only the enzyme levels but also the availability of their cofactors, e.g., NADPH, UDPGA (uridine diphosphate glucuronic acid), PAPS (3'-phosphoadenosine-5'-phosphosulfate), and GSH. Diets restricted in calories, protein, or essential fatty acids, as well as those having low quality protein or high sugar content, can affect the component enzymes, cytochrome P-450 and the cytochrome P-450 reductase, and the MFO activity toward a variety of drugs. In addition, deficiencies of specific vitamins (riboflavin, ascorbic acid, and vitamins A and E) and minerals (iron, copper, zinc, and magnesium) affect the components and activities of the system in unique ways. Insight into the regulation of the hepatic detoxification mechanism can be gained by using nutrient variables to perturb the system.
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PMID:Nutritional parameters that alter hepatic drug metabolism, conjugation, and toxicity. 351 Sep 12

Thirty-six wild-caught woodchucks (Marmota monax) were characterized according to sex, weight, trapping locality, liver pathology, and serum or hepatic markers of woodchuck hepatitis virus. Liver subcellular fractions were assayed for microsomal cytochromes P-450, aryl hydrocarbon hydroxylase, glutathione, cytosolic enzymes involved in its metabolism (glutathione S-transferase, glutathione peroxidase, and glutathione reductase), in the hexose monophosphate shunt (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase), NADH- and NADPH-dependent diaphorases, and DT diaphorase. Moreover, liver postmitochondrial fractions were assayed for their ability to activate procarcinogens [i.e., a tryptophan pyrolysate product, aflatoxin B1, 2-aminofluorene, and trans-7,8-dihydrobenzo(a)pyrene] to mutagenic metabolites in the Ames reversion test and to decrease the activity of direct-acting mutagens [i.e., 4-nitroquinoline N-oxide, 2-methoxy-6-chloro-9-[3-(2-chloroethyl)aminopropylamino]acridine X 2HCl, and sodium dichromate]. A considerable interindividual variability in metabolism was observed among the examined woodchucks. Some of the investigated parameters were more elevated in virus carriers, especially in those suffering from chronic active hepatitis, but only a few of the recorded differences (i.e., oxidized glutathione reductase and NADPH-dependent diaphorase) were statistically significant. The comparison of the monitored activities in woodchucks and in other rodent species (rat and mouse) led to the conclusion that the liver metabolism of mutagens and carcinogens in woodchucks is more oriented in the sense of activation, while detoxification mechanisms are more efficient in rats and mice.
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PMID:Metabolism of mutagens and carcinogens in woodchuck liver and its relationship with hepatitis virus infection. 360 50

We have studied the influence of hyperoxia and ageing on the activities of NADPH-cytochrome c reductase and glutathione S-transferase in different rat organs. Lung glutathione S-transferase activity increases markedly in 5-day-old pups exposed to hyperoxia, as observed for the O2- scavenging enzyme, superoxide dismutase. The levels of NADPH-cytochrome c reductase increase as well but after a 3-day lag period. In the liver, there is a pronounced decrease of both activities in 24-month-old rats, but at 12 months the activity of glutathione S-transferase increases whereas that of NADPH cytochrome c reductase activity decreases with respect to 3 months. The pattern of variations with age of NADPH cytochrome c reductase is similar in liver and brain. However the behaviour of brain glutathione S-transferase parallels that of the liver enzyme only up to 12 months. Thereafter the brain activity is maintained at a high level. These observations open the possibility that the high glutathione S-transferase levels in the old rat brain might be involved in protection towards oxidative alterations during ageing.
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PMID:Variations due to hyperoxia and ageing in the activities of glutathione S-transferase and NADPH-cytochrome c reductase. 361 86

Glutathione S-transferase (EC 2.5.1.18) was detected in the cytosolic and microsomal fractions of adult Dirofilaria immitis females at respective levels of 30 nmol and 3 nmol min-1 (mg protein)-1 activity with the substrate 1-chloro-2,4-dinitrobenzene (CDNB). The transferase activity in the cytosolic fraction of adult Brugia pahangi females was 10 nmol min-1 mg-1 with CDNB; determination of its activity in the microsomal fraction of this filariid was not attempted. These filarial glutathione S-transferases were further characterized after their purification by glutathione-affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the cytosolic transferase from D. immitis, molecular weight 47000, yielded a single subunit of around 28 kDa. The cytosolic and microsomal transferases from D. immitis differed in their activity with CDNB, 1,2-dichloro-4-nitrobenzene, 4-benzylchloride and ethacrynic acid. The cytosolic transferase from B. pahangi was distinguished by its high activity with ethacrynic acid. Both glutathione S-transferases from D. immitis also functioned as a glutathione peroxidase, strongly preferring cumene hydroperoxide as a substrate over hydrogen peroxide. Both were equiactive inhibitors of malonaldehyde formation in the NADPH-microsomal lipid peroxidation system. Thus, in addition to the ability of filarial glutathione S-transferases to detoxify electrophilic xenobiotics, at least those from D. immitis also exhibited selenium-independent glutathione peroxidase activity. Their glutathione S-transferase function suggests a potential role for these enzymes in the leukotriene synthetic pathway, if filariae can form such eicosanoids from arachidonate. Functioning as a glutathione peroxidase, they could serve to protect filarial membrane lipids from peroxidation.
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PMID:Glutathione S-transferase in adult Dirofilaria immitis and Brugia pahangi. 374 71

The activity of antioxidative enzymes SOD, catalase, glutathione peroxidase and the related glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-isocitrate dehydrogenase was examined in liver cytosol and large granule fraction (mitochondria) from control and copper-loaded rats. An increase of SOD activity (more than 100%) and a decrease of both catalase (by 60%) and glutathione peroxidase activity (by 30%) in large granule fraction were observed after copper loading. The cytosolic glutathione peroxidase activity was also markedly decreased: glutathione peroxidase I (EC 1.11.1.9)--by 35% and glutathione peroxidase II (EC 2.5.1.18)--by 75%. Cytosolic catalase activity and the glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-isocitrate dehydrogenase activities in cytosol and in mitochondria of copper-loaded rats were unchanged. It is concluded that under chronic copper loading the primary mechanisms of copper toxicity are accompanied by disturbances of the antioxidative enzyme function.
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PMID:Effect of chronic copper loading on the activity of rat liver antioxidative enzymes. 375 26

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

Water solubility and non-toxic properties of ascorbic acid are taken as criteria for beneficial effects of large doses of the vitamin. In the present study, male guinea pigs, dosed daily with 15, 30 or 50 mg/100g body weight for 10 weeks, demonstrated no differences in effect on liver and lung weights, body growth and microsomal protein contents of liver and lung when compared with controls. When guinea pigs were fed excessive ascorbic acid, there was a small non-significant increase (p less than 0.05) in hepatic and pulmonary cytochrome P-450, and significant increase (p less than 0.05) in hepatic cytochrome b5 which was accompanied with a significant increase in arylhydrocarbon hydroxylase activity in the two organs. Activity of NADPH-dependent cytochrome c-reductase was decreased in liver and remained unaffected in lung and colon. Drug detoxifying enzymes responded in different ways to increased intake of ascorbic acid. Activity of UDP-glucuronyltransferase remained unchanged on feeding excessive ascorbic acid, whereas glutathione S-transferase was decreased significantly in liver and was unaltered in lung and colon. Reduced glutathione was decreased only in the lung. The observed changes in drug activating and detoxifying enzymes appear to be important from drug pharmacokinetics and carcinogenesis point of view.
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PMID:Effect of large doses of ascorbic acid on the hepatic and extra-hepatic drug-metabolizing enzymes in guinea pig. 380 Oct 39


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