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 GSH-binding site of glutathione S-transferase (GST) isoenzymes was studied by investigating their substrate-specificity for three series of GSH analogues; further, a model of the interactions of GSH with the G-site is proposed. Twelve glycyl-modified GSH analogues, four ester derivatives of GSH and three cysteinyl-modified GSH analogues were synthesized and tested with purified forms of rat liver GST (1-1, 2-2, 3-3 and 4-4). The glycyl analogues exhibited spontaneous chemical reaction rates with 1-chloro-2,4-dinitrobenzene comparable with the GSH rate. In contrast, the enzymic rates (Vmax.) differed greatly, from less than 1 up to 140 mumol/min per mg; apparently, a reaction mechanism is followed that is very sensitive to substitutions at the glycyl domain. No correlation exists between the chemical rates and Vmax. values for the analogues. Analogues of GSH in which L-cysteine was replaced by D-cysteine, L-homocysteine or L-penicillamine showed little or no capacity to replace GSH as co-substrate for the GSTs. GSH monomethyl and monoethyl esters showed Vmax. values greater than the Vmax. measured with GSH: the Vmax. for the monoethyl ester of GSH and GST 3-3 was 5-fold that for GSH. The data obtained in this and previous studies [Adang, Brussee, Meyer, Coles, Ketterer, van der Gen & Mulder (1988) Biochem. J. 255, 721-724; Adang, Meyer, Brussee, van der Gen, Ketterer & Mulder (1989) Biochem. J. 264, 759-764] allow a model of the interactions of GSH in the G-site in GSTs to be postulated. The gamma-glutamyl site is the main binding determinant: the alpha-carboxylate group is obligatory, whereas shifting of the amino group and shortening of the peptide backbone only decreased kcat./Km. Furthermore, the GSTs appear to be very critical with respect to a correct orientation of the thiol group of the GSH analogue. The glycyl site is the least restrictive domain in the G-site of GSTs: amino acid analogues all showed Km values between 0.2 and 0.6 mM (that for GSH is 0.2-0.3 mM), but large differences in Vmax. exist. The glycyl carboxylate group is not essential for substrate recognition, since decarboxy analogues and ester derivatives showed high activities. The possible mechanisms for an increased Vmax. in some analogues are briefly discussed.
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PMID:The glutathione-binding site in glutathione S-transferases. Investigation of the cysteinyl, glycyl and gamma-glutamyl domains. 237 57

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

Chlamydomonas gametes of opposite mating types interact through flagellar adhesion molecules called agglutinins leading to a signal transduction cascade that induces cell wall loss and activation of mating structures along with other cellular responses that ultimately result in zygote formation. To identify molecules involved in these complex cellular events, we have employed subtractive and differential hybridization with cDNA from mt+ gametes activated for fertilization and non-signaling, vegetative (non-gametic) cells. We identified 55 cDNA clones whose transcripts were regulated in activated gametes. Here we report the molecular cloning and characterization of the complementary DNA (cDNA) for one clone whose transcripts in activated gametes were several-fold higher than in normal gametes. Regulation of the transcript was not related simply to protein synthesis because it was not increased in cells synthesizing new cell wall proteins. The cDNA contained a single open reading frame (ORF) of 815 amino acids encoding a polypeptide of calculated relative mass of 87 kDa. Database search analysis and sequence alignment indicated that the deduced amino acid sequence exhibited 42% identity and 62% similarity to a class of prokaryotic methyl transferases (5-methyltetrahydrofolate-homocysteine methyl transferase; EC 2.1.1.14) known to be involved in the terminal step of de novo biosynthesis of methionine. This enzyme catalyzes transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine resulting in methionine formation. Affinity-purified polyclonal antibodies raised against a bacterially produced GST-fusion protein identified a 85 kDa soluble protein in Chlamydomonas gametes. Southern blot hybridization indicated that the enzyme is encoded by a single-copy gene. The evidence presented in this paper raises the possibility that, in addition to its participation in de novo biosynthesis and regeneration of methionine, Chlamydomonas methionine synthase may play a role in adhesion-induced events during fertilization.
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PMID:Increased transcript levels of a methionine synthase during adhesion-induced activation of Chlamydomonas reinhardtii gametes. 861 21

Homocysteine is a neurotoxic non-proteinogenic amino acid, an abnormal increase of which in plasma has been implicated in many pathological conditions including cardiovascular diseases, neural tube defects and is now recognized and Alzheimer's disease. Homocysteine elimination is regulated by the transmethylation and the transsulfuration pathways and is modulated by folate, a member of the B-vitamin family. A metabolic product of folate, 5 methyltetrahydrofolate, provides a methyl group that is used to reconvert homocysteine back to methionine through the transmethylation pathway. The efficiency of folate metabolism has an impact on the availability of S-adenosylmethionine (SAM), a compound that is known to activate homocysteine flux through the transsulfuration pathway. SAM is also necessary for utilization of the antioxidant glutathione via glutathione S-transferase. In this review, I will elaborate on different biochemical reactions that are implicated in the regulation of homocysteine elimination through the transmethylation and the transsulfuration pathways and on various consequences of folate deficiency on homocysteine metabolism.
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PMID:Homocysteine metabolism and various consequences of folate deficiency. 1691 51

Saccharomyces cerevisiae cells contain three omega-class glutathione transferases with glutaredoxin activity (Gto1, Gto2, and Gto3), in addition to two glutathione transferases (Gtt1 and Gtt2) not classifiable into standard classes. Gto1 is located at the peroxisomes, where it is targeted through a PTS1-type sequence, whereas Gto2 and Gto3 are in the cytosol. Among the GTO genes, GTO2 shows the strongest induction of expression by agents such as diamide, 1-chloro-2,4-dinitrobenzene, tert-butyl hydroperoxide or cadmium, in a manner that is dependent on transcriptional factors Yap1 and/or Msn2/4. Diamide and 1-chloro-2,4-dinitrobenzene (causing depletion of reduced glutathione) also induce expression of GTO1 over basal levels. Phenotypic analyses with single and multiple mutants in the S. cerevisiae glutathione transferase genes show that, in the absence of Gto1 and the two Gtt proteins, cells display increased sensitivity to cadmium. A gto1-null mutant also shows growth defects on oleic acid-based medium, which is indicative of abnormal peroxisomal functions, and altered expression of genes related to sulfur amino acid metabolism. As a consequence, growth of the gto1 mutant is delayed in growth medium without lysine, serine, or threonine, and the mutant cells have low levels of reduced glutathione. The role of Gto1 at the S. cerevisiae peroxisomes could be related to the redox regulation of the Str3 cystathionine beta-lyase protein. This protein is also located at the peroxisomes in S. cerevisiae, where it is involved in transulfuration of cysteine into homocysteine, and requires a conserved cysteine residue for its biological activity.
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PMID:A peroxisomal glutathione transferase of Saccharomyces cerevisiae is functionally related to sulfur amino acid metabolism. 1693 41

When maintained on a folate-deficient, iron-rich diet, transgenic mice lacking in apolipoprotein E (ApoE-/- mice) demonstrate impaired activity of glutathione S-transferase (GST), resulting in increased oxidative species within brain tissue despite abnormally high levels of glutathione. These mice also exhibit reduced levels of S-adenosyl methionine (SAM) and increased levels of its hydrolysis product S-adenosyl homocysteine, which inhibits SAM usage. Supplementation of the above diet with SAM restored GST activity and eliminated reactive oxygen species at the expense of stockpiled glutathione, suggesting that one or more SAM-dependent reactions were required to maintain GST activity. We examined herein the impact of SAM on GST activity using a cell-free assay. SAM stimulated GST activity in a dose-response manner when added to homogenates derived from the above ApoE-/- mice. SAM also increased activity of purified rat liver GST and recombinant GST. Filtering of SAM through a 4 kDa cutoff and systematic withholding of reaction components eliminated the possibility of any additional contaminating enzyme. These findings confirm that SAM can exert a direct effect on GST activity. Since Alzheimer's disease is accompanied by reduced GST activity, diminished SAM and increased SAH, these findings underscore the critical role of SAM in maintenance of neuronal health.
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PMID:S-adenosylmethionine mediates glutathione efficacy by increasing glutathione S-transferase activity: implications for S-adenosyl methionine as a neuroprotective dietary supplement. 1859 58

Folate deficiency is associated with increase in homocysteine levels. Abnormal plasma levels of that neurotoxic nonproteinogenic amino acid is implicated in many pathological conditions including cardiovascular diseases, neural tube defects, and is now recognized as a risk factor in Alzheimer's disease (AD) dementia. Homocysteine elimination is regulated by two metabolic pathways, namely, the transmethylation and the transsulfuration pathways. Its elimination via these two metabolic pathways is modulated by folate, a member of the B-vitamin family. Folate provides, via its metabolic end product 5-methyltetrahydrofolate, a methyl group that is used to reconvert homocysteine back to methionine through the transmethylation pathway. The efficiency of folate metabolism has an impact on the availability of S-adenosylmethionine, a compound that is known to activate homocysteine flux through the transsulfuration pathway and is necessary for utilization of a downstream antioxidant called glutathione under the catalysis of glutathione S-transferase enzyme. In this review, we will explore the impact of folate deprivation on the regulation of the methionine cycle and exhaustively describe different biochemical reactions that are implicated in the regulation of homocysteine elimination and that folate deficiency influences in AD neuropathology.
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PMID:Folate deprivation, the methionine cycle, and Alzheimer's disease. 1880 92

Very recent findings confirmed that S-adenosylmethionine (SAM) can exert a direct effect on glutathione S-transferase (GST) activity. Alzheimer's disease (AD) is accompanied by reduced GST activity, diminished SAM, and increased S-adenosyl homocysteine (SAH), the downstream metabolic product resulting from SAM-mediated transmethylation reactions, when deprived of folate. Therefore, these findings underscored the critical role of SAM in maintenance of neuronal health, suggesting a possible role of SAM as a neuroprotective dietary supplement in AD. Given recent findings from clinical trials in which omega-3 polyunsturated fatty acids (PUFA) supplementation was effective only in very mild AD subgroups or mild cognitive impairment (MCI), we suggest intervention trials using measures of dietary supplementation (dietary omega-3 PUFA and SAM plus B vitamin supplementation) to determine if such supplements will reduce the risk for cognitive decline in very mild AD and MCI. Therefore, key supplements are not necessarily working in isolation, and the most profound impact, or in some cases the only impact, is noted very early in the course of AD, suggesting that nutriceutical supplements may bolster pharmacological approaches well past the window where supplements can work on their own.
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PMID:Possible role of S-adenosylmethionine, S-adenosylhomocysteine, and polyunsaturated fatty acids in predementia syndromes and Alzheimer's disease. 1927 39

There is growing evidence that docetaxel, a microtubule-targeting agent like the other taxane paclitaxel, induces dual cytotoxicity mechanism according to dose level. Postgenomics screening technologies are now more and more applied to the elucidation of drug response mechanisms. Proton nuclear magnetic resonance spectroscopy-based pharmacometabolomics was here applied to get further insight into the response of human MCF7 breast carcinoma cells to docetaxel at high (clinical, 5 microM) and low (1 nM) doses. The global response to both doses was evaluated by nuclear morphology and DNA content, the latter as an index of cell proliferation and DNA ploidy. High dose provoked long-lasting cell cycle arrest in mitosis during the first 48 h of exposure to treatment and severe decrease in DNA content followed by significant amount of cell death. In contrast, at low dose, no long-lasting cell cycle arrest was observed on micrographies, and DNA content was decreased but less than at high dose (P < 0.05), without significant cell death. This response was compared to biochemical alteration assessed by pharmacometabolomics. Thirty metabolites were identified and quantified. Metabolite profiling at clinical dose revealed time-dependent disorders in derivatives of glycolysis, lipid metabolism and glutathione metabolism. Comparison between high and low doses was performed at 72 h and showed common traits including the accumulation of cytidinediphosphocholine (x 5.0 and x 6.9, respectively, P < 0.03), the decrease in phosphatidylcholine (x 0.3 and x 0.2, respectively, P < 0.03), and gluthathione (x 0.6 and x 0.6, respectively, P < 0.03). Despite that, significant dose-dependent differences were found in 12 of 30 measured metabolites. Among them, the most discriminant metabolites were polyunsaturated fatty acids (ratio of high-to-low dose of 14.8, P < 0.05), glutamate, myoinositol, and homocysteine (ratio < 0.4, P < 0.05). In addition, the mechanism for glutathione decrease was different. At high dose, it resulted from extensive consumption with precursor starvation (glutamate: -89%, P < 0.05) and increased glutathione S-transferase activity (x 5, P < 0.01), whereas at low dose, it resulted from glutathione biosynthesis blockade with homocysteine accumulation (+144%, P < 0.03) and decreased glutathione S-transferase activity (-70%, P < 0.01). Altogether, this pharmacometabolomics analysis provides further evidence of the varying cellular responses at high and low doses of docetaxel in MCF7 breast cancer cells.
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PMID:Pharmacometabolomics of docetaxel-treated human MCF7 breast cancer cells provides evidence of varying cellular responses at high and low doses. 1951 27

Pathways for tailoring and processing vitamins into active cofactor forms exist in mammals that are unable to synthesize these cofactors de novo. A prerequisite for intracellular tailoring of alkylcobalamins entering from the circulation is removal of the alkyl group to generate an intermediate that can subsequently be converted into the active cofactor forms. MMACHC, a cytosolic cobalamin trafficking chaperone, has been shown recently to catalyze a reductive decyanation reaction when it encounters cyanocobalamin. In this study, we demonstrate that this versatile protein catalyzes an entirely different chemical reaction with alkylcobalamins using the thiolate of glutathione for nucleophilic displacement to generate cob(I)alamin and the corresponding glutathione thioether. Biologically relevant thiols, e.g. cysteine and homocysteine, cannot substitute for glutathione. The catalytic turnover numbers for the dealkylation of methylcobalamin and 5'-deoxyadenosylcobalamin by MMACHC are 11.7 +/- 0.2 and 0.174 +/- 0.006 h(-1) at 20 degrees C, respectively. This glutathione transferase activity of MMACHC is reminiscent of the methyltransferase chemistry catalyzed by the vitamin B(12)-dependent methionine synthase and is impaired in the cblC group of inborn errors of cobalamin disorders.
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PMID:A human vitamin B12 trafficking protein uses glutathione transferase activity for processing alkylcobalamins. 1980 55


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