Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GSTs”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2005

Novel functional association of rat testicular membrane-associated cytosolic glutathione S transferases and cyclooxygenase in vitro.

AIM: To analyze the role of cytosolic glutathione S-transferases cGSTs and membrane-associated cytosolic GSTs macGSTs in prostaglandin biosynthesis and to evaluate the possible interaction between glutathione S-transferases GSTs and cyclooxygenase (COX) in vitro. METHODS: SDS-PAGE analysis was undertaken for characterization of GSTs, thin layer chromatography (TLC) to monitor the effect of GSTs on prostaglandin biosynthesis from arachidonic acid (AA) and spectrophotometric assays were done for measuring activity levels of COX and GSTs. RESULTS: SDS-PAGE analysis indicates that macGSTs have molecular weights in the range of 25-28 kDa. In a coupled assay involving GSTs, arachidonic acid and cyclooxygenase-1, rat testicular macGSTs produced prostaglandin E2 and F2alfa, while the cGSTs caused the generation of prostaglandin D2, E2 and F2alfa. In vitro interaction studies on GSTs and COX at the protein level have shown dose-dependent inhibition of COX activity by macGSTs and vice versa. This effect, however, is not seen with cGSTs. The inhibitory effect of COX on macGST activity was relieved with increasing concentrations of reduced glutathione (GSH) but not with 1-chloro 2,4-dinitrobenzene (CDNB). The inhibition of COX by macGSTs, on the other hand, was potentiated by glutathione. CONCLUSION: We isolated and purified macGSTs and cGSTs from rat testis and analyzed their involvement in prostaglandin biosynthesis. These studies reveal a reversible functional interaction between macGSTs and COX in vitro, with possible interactions between them at the GSH binding site of macGSTs.

Animals↗
PubMed2002

Plant glutathione transferases.

SUMMARY: The soluble glutathione transferases (GSTs, EC 2.5.1.18) are encoded by a large and diverse gene family in plants, which can be divided on the basis of sequence identity into the phi, tau, theta, zeta and lambda classes. The theta and zeta GSTs have counterparts in animals but the other classes are plant-specific and form the focus of this article. The genome of Arabidopsis thaliana contains 48 GST genes, with the tau and phi classes being the most numerous. The GST proteins have evolved by gene duplication to perform a range of functional roles using the tripeptide glutathione (GSH) as a cosubstrate or coenzyme. GSTs are predominantly expressed in the cytosol, where their GSH-dependent catalytic functions include the conjugation and resulting detoxification of herbicides, the reduction of organic hydroperoxides formed during oxidative stress and the isomerization of maleylacetoacetate to fumarylacetoacetate, a key step in the catabolism of tyrosine. GSTs also have non-catalytic roles, binding flavonoid natural products in the cytosol prior to their deposition in the vacuole. Recent studies have also implicated GSTs as components of ultraviolet-inducible cell signaling pathways and as potential regulators of apoptosis. Although sequence diversification has produced GSTs with multiple functions, the structure of these proteins has been highly conserved. The GSTs thus represent an excellent example of how protein families can diversify to fulfill multiple functions while conserving form and structure.

Arabidopsis↗
PubMed1993

Significance of an unusually low Km for glutathione in glutathione transferases of the alpha, mu and pi classes.

1. Interactions of glutathione transferases (GST) of the alpha, mu and pi classes with glutathione (GSH) and glutathione conjugates (GS-X) are in contrast with those of a GST of the theta class (GST5-5). 2. GST 5-5 has a Km for GSH of approx. 5 mM. Thus Km/ambient [GSH] is approx. 1, within the range of Km/ambient [s] of glycolytic enzymes. GSTs of the alpha, mu and pi classes yield much lower values of Km for GSH (approx. 0.1 mM) hence Km/ambient [s] is significantly lower than those of most (non-GST) enzymes (p < 0.025). 3. GSTs of the alpha, mu and pi classes are sensitive to inhibition by GS-X (i.e. product) and GS-X analogues. GST 5-5 is not. 4. Rate enhancements up to 10(10), similar to an average enzyme (10(8)-10(12)), are seen in catalysis by GST 5-5, but not in catalysis by GSTs of alpha, mu and pi classes (> 10(7)). 5. Comparisons of primary structure indicate that theta class GSTs may have a decreased binding of the glu-alpha-amino- and gly-COO(-)-groups of GSH compared with GSTs of the other classes. 6. It is concluded that GSTs of alpha, mu and pi classes have evolved towards increased product binding at the expense of catalytic efficiency. Thus GSH is uniquely utilized both as a nucleophile and a 'tag' which can be used to bind and sequester product particularly during GSH-depletion. This interpretation unifies the catalytic and binding properties of these GSTs and alters their perceived role in detoxication.

Adaptation, Physiological↗
PubMed2002

[Effects of exposure to asbestos on plasma activity of glutathione S-transferases].

OBJECTIVE: To understand the effects of exposure to asbestos and GSTM1 genotypes on plasma activity of glutathione S-transferases (GSTs). METHODS: Ninety-four workers exposed to asbestos and 51 controls were selected, and their general information, occupational history and personal behavior were collected by questionnaire. Venous blood specimen was collected from each of them and plasma was separated for detection of GSTs activity and lymphocytes for DNA extraction and GSTM1 genotyping. RESULTS: Plasma activity of GSTs in the asbestos-exposed workers (23.0 +/- 6.9) U/L was significantly lower than that in the controls (32.6 +/- 11.8) U/L, which declined with the length of employment in asbestos industry and the increase of cumulated dose of asbestos. Stratification of workers by GSTM1 genotypes showed that plasma activity of GSTs in asbestos-exposed workers with GSTM1+/+ or GSTM1-/- were (24.0 +/- 6.1) and (22.5 +/- 7.3) U/L, respectively, lower than those in the controls with the same genotypes (38.1 +/- 13.2) and (26.8 +/- 6.6) U/L. Plasma activity of GSTs in the control workers with GSTM-/- was significantly lower than in those with GSTM+/+, and, so did in asbestos-exposed workers, but without statistically significant difference. CONCLUSION: Exposure to asbestos could significantly decrease plasma activity of GSTs, and GSTM1 genotypes could affect on the activity of GSTs in the control workers, which was not so obvious in asbestos-exposed workers.

Adult↗
PubMed1992

Gene-specific oligonucleotide probes for alpha, mu, pi, and microsomal rat glutathione S-transferases: analysis of liver transferase expression and its modulation by hepatic enzyme inducers and platinum anticancer drugs.

Glutathione S-transferases (GSTs) play an important role in the detoxification of diverse electrophilic chemicals, including anticancer drugs. Gene-specific oligonucleotide probes were developed to monitor the expression of individual GST mRNAs in livers of adult male rats treated with drugs and other chemical modulators of GST expression. Northern blot analysis of total liver RNA using probes specific for individual GSTs belonging to classes alpha (GSTs Ya1, Ya2, Yc), mu (GSTs Yb1, Yb2, Yb3), pi (GST Yp), and GSTms demonstrated the expression in liver of all but Yp mRNA. Kidney GST expression was at least as high as that in liver for GSTs Ya1, Yc, and Yp, while it was substantially lower but still detectable for GSTs Ya2, Yb2, and GSTms. Several of the liver GST class alpha mRNAs, in particular Ya2, were inducible by pretreatment of rats with phenobarbital or isosafrole. In contrast, dexamethasone preferentially induced Yb1, Yb2, and Ya2, while two other inducers of liver drug metabolism, isoniazid and clofibrate, were less effective with respect to GST induction. GSTms mRNA was induced to a small extent or not at all by the agents tested. Treatment of adult male rats with the anticancer drug cisplatin increased liver expression of GST Yc mRNA and suppressed Ya1 mRNA levels with little or no major effect on several other GST mRNAs. Western blot analysis of liver cytosols prepared from the cisplatin-treated rats revealed corresponding changes in GST Yc and Ya protein levels. Comparable changes in liver GST Ya1 and Yc expression were effected by the cisplatin analogue iproplatin but not by carboplatin or transplatin. This pattern of response to these platinum drugs is comparable to that seen with respect to platinum drug-induced gonadal toxicity and modulation of liver cytochrome P450 expression, suggesting a common mechanistic basis for these diverse effects of platinum anticancer drugs on hepatic enzymes of drug metabolism. Together, these studies demonstrate the utility of oligonucleotide probes for phenotyping liver tissue for the expression of GST enzymes that can contribute to anticancer drug metabolism and resistance. They also raise the possibility of drug-drug interactions involving cisplatin and alkylating agent anticancer drugs that can be metabolized in liver by alpha-class GSTs.

Animals↗
PubMed1992

Glutathione transferase isoenzymes from Bufo bufo embryos at an early developmental stage.

Six forms of glutathione transferase (GST) were resolved from the cytosolic fraction of Bufo bufo embryos at developmental stage 4 by GSH-Sepharose affinity chromatography followed by f.p.l.c. chromatofocusing in the 9-6 pH range. They have apparent isoelectric points at pH 8.37 (GST I), 8.22 (GST II), 8.10 (GST III), 7.84 (GST IV), 7.37 (GST V) and 7.12 (GST VI), and each displayed an apparent subunit molecular mass of 23 kDa by SDS/PAGE. The Bufo bufo embryo enzymes showed very similar structural, catalytic and immunological properties, as indicated by their substrate-specificities, inhibition characteristics, c.d. spectra, h.p.l.c. elution profiles and immunological reactivities, as well as by their N-terminal amino acid sequences. Although Bufo bufo embryo GSTs do not correspond to any other known GSTs, the results of our experiments indicate that amphibian GSTs could be included in the Pi family of GSTs. This conclusion is supported by the analysis of c.d. spectra, and by the fact that mammalian Pi class GSTs and amphibian GSTs showed about 80% identity in their N-terminal amino acid sequences. Furthermore, antisera prepared against Bufo bufo GST III cross-reacted in immunoblotting analysis with Pi class GSTs, and vice versa.

Amino Acid Sequence↗
PubMed1990

A distinct human testis and brain mu-class glutathione S-transferase. Molecular cloning and characterization of a form present even in individuals lacking hepatic type mu isoenzymes.

mu-Class glutathione S-transferases (GSTs) were identified in all 13 human testes and 28 brains examined; even subjects whose livers were devoid of mu-GSTs expressed extrahepatic GSTs of this class. Testes and brains from individuals with mu-class GSTs in their livers had additional forms that also reflected the liver phenotypes. An isoenzyme with an isoelectric point of 5.2, which was a major GST in testis and present as well in cerebral cortex but not detected in any livers, was identified and purified. Sequence analysis of peptides derived by cleavage of the testicular mu-class GST by Achromobacter protease I revealed distinct aspects of primary structure not found previously in any mammalian mu-class GSTs. These unique features included a blocked and extended amino terminus and 3 additional residues (Pro-Val-Cys) at the carboxyl terminus. This structure was confirmed by molecular cloning and sequencing of cDNAs derived from human testis and brain libraries. In the coding region the mRNA of the brain-testis mu-class GST was 75% homologous with that of the liver form, and its 3'-untranslated sequence was mostly divergent, indicating that it is the product of a separate gene. Distinct catalytic and structural properties of the testis-brain mu-class GSTs suggest that these GSTs may be uniquely involved in blood-barrier functions common to both organs.

Adolescent↗
PubMed1993

[Glutathione S-transferases in carcinogenesis and diagnosis of liver cancer].

We studied the relations between glutathione S-transferases (GSTs) from human liver and hepatic cancer and preneoplastic lesions in high risk area of Qidong city and Beijing. A biotin-avidin enzyme-linked immunoassay (BA-ELISA) for serum level of GSTs was developed. The results showed that the GSTs level of normal controls in Qidong city (0.66 +/- 0.54 ng/ml) was higher than that in Beijing (0.37 +/- 0.27 ng/ml). The members of high cancer families, HBVsAg carries and patients having a low level fluctuating pattern of serum AFP were the population with high risk of liver cancer; their serum level of GSTs was 1.25 +/- 1.46, 1.43 +/- 1.44 and 2.81 +/- 1.76 ng/ml respectively, and it was significantly higher than in the normal controls. The content of GSTs of hepatic cancer patients in Qidong city and Beijing was 3.03 +/- 3.35 and 3.60 +/- 3.70 ng/ml respectively, but the positive rate (97%) of GSTs in Qidong city was higher than that (82%) in Beijing. The results suggested that serum expression of GSTs can be used as an enzyme marker for hepatic cancer and preneoplastic lesions. Possible roles of these forms in hepatic carcinogenesis induced by chemical carcinogenesis were discussed.

Biomarkers, Tumor↗
PubMed2025

Coordinated regulation of glutathione S-transferases confers metabolic flexibility in multi-insecticide-resistant Frankliniella occidentalis (Pergande).

INTRODUCTION: The evolution of multi-insecticide resistance in insect pests threatens global food security. Although glutathione S-transferases (GSTs) are implicated in detoxification, the coordinated mechanism by which specific gene subfamilies interact to confer broad-spectrum resistance remains inadequately characterized. OBJECTIVE: To dissect the functional allocation and cooperation of GST subfamilies in multi-insecticide-resistant strains of Frankliniella occidentalis. METHODS: We integrated comparative genomics (20 GST genes cloned), transcriptomics (qRT-PCR), RNAi-mediated silencing, molecular docking (AutoDock Vina), and in vitro metabolism assays (UPLC-MS/MS) across susceptible and resistant thrips strains. RESULTS: The two resistant strains (NIL-R and FS-R) exhibited moderate to high resistance to five insecticides (chlorfenapyr, emamectin benzoate, spinetoram, spinosad, and thiamethoxam), accompanied by significantly elevated GSTs activity. Phylogenetic analysis indicates that GSTs include 10 conserved delta and 7 diverse sigma members. The sigma subfamily has undergone a marked expansion due to gene duplication. Delta (FoGSTd1, d4, and d9) and sigma (FoGSTs1, s2, and s6) genes were significantly up-regulated in the resistant strains. RNAi showed specialized functional allocation among GSTs: delta GSTs mediated resistance to spinosad and chlorfenapyr, sigma GSTs were responsible for thiamethoxam resistance, and notably, cooperation between these subfamilies contributed to resistance against emamectin benzoate and spinetoram. Molecular docking and in vitro metabolism assays of FoGSTd9 and FoGSTs1 proteins further supported the functional allocation and cooperative roles of GST subfamilies. CONCLUSION: Our results indicate that F. occidentalis may coordinate GST subfamilies to achieve metabolic flexibility in response to multi-insecticide pressure. This survival strategy, mediated by mechanistic functional allocation and cooperative interactions among subfamilies, may contribute to energy conservation and reduced adaptive costs. Disruption of this coordinated mechanism represents a potential approach for overcoming resistance in agricultural pest populations.

Animals↗
PubMed1999

Global statistical tests for comparing multiple outcomes in rheumatoid arthritis trials. MIRA Trial Group.

OBJECTIVE: To evaluate global statistical tests (GSTs) of treatment effectiveness for rheumatoid arthritis (RA) trials measuring multiple outcomes. METHODS: Using outcome measures from American College of Rheumatology (ACR) core set variables available in 3 RA trials, GSTs were calculated using the O'Brien ranking procedure and a procedure for binary data. GSTs take correlations among outcomes into account. Power calculations using 1 trial data set provide comparisons of GSTs and ACR criteria for improvement. RESULTS: Spearman correlations among outcomes ranged from 0.21 to 0.73. Erythrocyte sedimentation rate had the lowest correlation with other outcomes in all 3 trials. Within a trial, joint swelling and joint tenderness or patient and physician assessment had the highest correlations, depending on the trial. Results were consistent with results using the ACR criteria, although the GST was more powerful. CONCLUSION: GSTs are a useful tool for comparing treatment effects across multiple clinically meaningful outcome measures. The GST allows easy inclusion of validated, reliable new measures that are not a part of ACR criteria, such as quality of life, and can be computed with or without selecting a cutoff point defining patient improvement. GSTs should be considered for rheumatic disease treatment trials.

Arthritis, Rheumatoid↗
PubMed1997

Differential catalytic efficiency and enantioselectivity of murine glutathione S-transferase isoenzymes in the glutathione conjugation of carcinogenic anti-diol epoxides of chrysene and benzo(g)chrysene.

The kinetics of the conjugation of carcinogenic anti-diol epoxides of chrysene (anti-CDE) and benzo(g)chrysene [anti-B(g)CDE] with glutathione (GSH) catalyzed by GSH S-transferase (GST) isoenzymes mGSTP1-1, mGSTM1-1, mGSTA3-3, mGSTA4-4, and GST 9.5 of female A/J mouse tissues has been investigated. When GST activity was measured as a function of varying anti-CDE or anti-B(g)-CDE concentrations at a fixed concentration of GSH, each isoenzyme obeyed Michaelis-Menten kinetics. The catalytic efficiencies (k(cat)/Km) of murine GSTs in the GSH conjugation of anti-CDE were in the order of GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3 > mGSTA4-4. While each GST isoenzyme examined in the present study exhibited preference for the GSH conjugation of (+)-anti-CDE with the (R,S)-diol (S,R)-epoxide absolute configuration, which is a far more potent carcinogen than the (-)-anti-CDE [(S,R)-diol (R,S)-epoxide absolute configuration], the enantioselectivity was relatively more pronounced for mGSTP1-1 compared with other murine GSTs. Anti-B(g)CDE was a relatively poor substrate for each GST isoenzyme examined compared with anti-CDE. The catalytic efficiencies of murine GSTs in the GSH conjugation of anti-B(g)CDE were in the order of GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3. With the exception of mGSTM1-1, all other murine GSTs exhibited preference for the GSH conjugation of anti-B(g)CDE enantiomer with the (R,S)-diol (S,R)-epoxide absolute configuration. In summary, the results of the present study indicate that the murine GSTs significantly differ in their catalytic efficiency and enantioselectivity in the GSH conjugation of both anti-CDE and anti-B(g)CDE, and that anti-B(g)CDE is a relatively poor substrate for murine GSTs compared with anti-CDE, which may partially account for the observed relatively higher carcinogenic potency of the former compound.

Animals↗
PubMed1993

Activity of mouse liver glutathione S-transferases toward trans,trans-muconaldehyde and trans-4-hydroxy-2-nonenal.

This study investigated the catalytic activities of hepatic glutathione S-transferase (GST) isoenzymes isolated from CD-1 mice toward two activated alkenals of toxicological relevance: trans,trans-muconaldehyde (MA), a putative myelotoxic metabolite of benzene, and trans-4-hydroxy-2-nonenal (HNE), a highly reactive lipid peroxidation product. The activity toward 1-chloro-2,4-dinitrobenzene (CDNB) was also determined. Four isoenzymes with pI values of 9.8, 8.7, 6.4, and 5.7 were each isolated from male and female mice. The isoenzymes with pI values of 8.7 and 6.4 are pi and mu class GSTs, respectively, whereas the pI 9.8 and 5.7 GSTs are both alpha class isoenzymes. CDNB activity was greatest in the pi (pI 8.7) isoenzyme of both sexes. In addition, the CDNB activity of the pi (pI 8.7) isoenzyme from males was markedly greater than the corresponding GST from female mouse liver. In contrast to CDNB, both MA and HNE were better substrates for the acidic alpha (pI 5.7) and mu (pI 6.4) GSTs, whereas minimal activity toward either alkenal was detected in the pi (pI 8.7) and alpha (pI 9.8) isoenzymes. Maximum activity toward MA and HNE was exhibited by the alpha (pI 5.7) isoenzyme of both sexes. The level of HNE activity observed with the alpha (pI 5.7) isoenzyme was five- to sixfold greater than that reported previously for any mouse GST isoenzyme. Moreover, the specific activities of the female alpha (pI 5.7) isoenzyme toward both HNE and MA were markedly greater than those of the corresponding isoenzyme from males. A similar gender-specific difference was noted in the activity of the mu (pI 6.4) isoenzyme toward HNE, but not toward MA. These results show that both MA and HNE are substrates for the alpha (pI 5.7) and mu (pI 6.4) GSTs of murine liver, with maximum activity toward both activated alkenals exhibited by the alpha (pI 5.7) isozyme. In addition, evidence is presented that demonstrates a female-dominant sex difference in the activity of the alpha (pI 5.7) isoenzyme toward MA and HNE, which contrasts sharply with the male-dominant activity of pi class GSTs toward CDNB. These results are consistent with the hypothesis that alpha and mu class GSTs are critical detoxication enzymes in female mouse liver, whereas pi-class GST isozymes predominate in the liver of male mice.

Aldehydes↗
PubMed1996

Glutathione S-transferase-catalyzed conjugation of bioactivated aflatoxin B1 in rabbit lung and liver.

Aflatoxin B1 (AFB1) requires bioactivation to AFB1-8,9-epoxide for carcinogenicity, and glutathione S-transferase (GST)-catalyzed conjugation of activated AFB1 with glutathione (GSH) is a critical determinant of susceptibility to the mycotoxin. Incubations containing [3H]AFB1, rabbit liver microsomes, an NADPH-generating system, 1 mM GSH, and GST-containing lung or liver cytosol were performed to assess the abilities of lung and liver GSTs to conjugate AFB1-8,9-epoxide. [3H]AFB1-GSH was isolated by isocratic reverse-phase high-performance liquid chromatography (HPLC) and quantitated by liquid scintillation spectroscopy. Maximal [3H]AFB1-GSH formation rates were significantly lower for lung than for liver (0.3 +/- 0.1 and 1.7 +/- 0.4 nmol/mg/hr, respectively). Immunoprecipitation of rabbit pulmonary cytosolic GSTs with anti-alpha or anti-mu GST antisera decreased [3H]AFB1-GSH production by approximately 45 and 51%, respectively, indicating that alpha-class and mu-class GSTs are of similar importance in catalyzing this reaction in the lung. Because mu-class GSTs comprise only a small proportion of total lung GST content, these enzymes have high specific activity toward AFB1-8,9-epoxide. In contrast, the pi-class GST appeared to play a negligible role. Using a rat liver microsomal system to generate both AFB1 exo- and endoepoxide isomers, and analysis based on chiral HPLC, we found that rabbit liver cytosolic GSTs catalyzed formation of both AFB1 exo- and endo-epoxide-GSH conjugates, whereas pulmonary cytosolic GSTs catalyzed formation of only the exo stereoisomer at detectable levels. Despite a preference for conjugating the more mutagenic AFB1 exo-epoxide isomer, the relatively low capacity for GST-catalyzed detoxification of bioactivated AFB1 in lung may be an important factor in the susceptibility of the lung to AFB1 toxicity.

Aflatoxin B1↗
PubMed1995

Glutathione S-transferases from larval Manduca sexta midgut: sequence of two cDNAs and enzyme induction.

Two glutathione S-transferase (GST) clones from a larval midgut cDNA library of the tobacco hornworm, Manduca sexta were sequenced. The nucleotide sequence of the first clone, M. sexta GST1, encoded a protein of 217 amino acids with a predicted molecular weight of 24,644 and isoelectric point of 4.8. The M. sexta GST1 was 45.9-48.6% identical to GSTs from Musca domestica and several Drosophila species. The M. sexta GST2 cDNA encoded a protein of 203 amino acids with a predicted molecular weight of 23,596 and isoelectric point of 5.5. The M. sexta GST2 shared 44.8-50.0% sequence identity to a second cluster of insect GSTs from M. domestica, D. melanogaster and Anopheles gambiae. GST1 and GST2 were only 24.1% identical in amino acid sequence. The divergence of these two classes of insect GSTs occurred before the radiation of Diptera and Lepidoptera. Northern analysis of the expression of these GSTs showed increased GST1 mRNA levels in midguts of larvae fed diets containing 2-undecanone, or phenobarbital. Midgut and fat body cytosolic GST activities were induced when larvae were fed diets containing 2-tridecanone, 2-undecanone, or phenobarbital. Partial purification of midgut GSTs by size-exclusion and glutathione affinity chromatography resulted in a series of isoelectric focusing bands, with the major one corresponding to the predicted isoelectric point of the M. sexta GST1. In summary, two midgut GSTs have been identified on the basis of cDNA sequence and one of these, GST1, was inducible by dietary chemicals.

Amino Acid Sequence↗
PubMed2005

Modulation of xenobiotic metabolising enzymes by anticarcinogens -- focus on glutathione S-transferases and their role as targets of dietary chemoprevention in colorectal carcinogenesis.

There is evidence that consumption of certain dietary ingredients may favourably modulate biotransformation of carcinogens. Associated with this is the hypothesis that the risk for developing colorectal cancer could be reduced, since its incidence is related to diet. Two main groups of biotransformation enzymes metabolize carcinogens, namely Phase I enzymes, which convert hydrophobic compounds to more water-soluble moieties, and Phase II enzymes (e.g. glutathione S-transferases [GST]), which primarily catalyze conjugation reactions. The conjugation of electrophilic Phase I intermediates with glutathione, for instance, frequently results in detoxification. Several possible colon carcinogens may serve as substrates for GST isoenzymes that can have marked substrate specificity. The conjugated products could be less toxic/genotoxic if GSTs are induced, thereby reducing exposure. Thus, numerous studies have shown that the induction of GSTs by antioxidants enables experimental animals to tolerate exposure to carcinogens. One important mechanism of GST induction involves an antioxidant-responsive response element (ARE) and the transcription factor nuclear factor E2-related factor 2 (Nrf2), which is bound to the Kelch-like ECH associated protein 1 (Keap1) in the cytoplasm. Antioxidants may disrupt the Keap-Nrf2 complex, allowing Nrf2 to translocate to the nucleus and mediate expression of Phase II genes via interaction with the ARE. GSTs are also induced by butyrate, a product of gut flora-derived fermentation of plant foods, which may act via different mechanisms, e.g. by increasing histone acetylation. GSTs are expressed with high inter-individual variability in human colonocytes, which points to large differences in cellular susceptibility to xenobiotics. Enhancing expression of GSTs in human colon tissue could therefore contribute to reducing cancer risks. However, it has not been demonstrated in humans that this mechanism is associated with cancer prevention. In the future, it will be useful to determine GSTs during dietary intervention studies to enhance our understanding of this protective mechanism.

Anticarcinogenic Agents↗
PubMed2002

Synthesis and characterization of 6-chloroacetyl-2-dimethylaminonaphthalene as a fluorogenic substrate and a mechanistic probe for glutathione transferases.

Here we demonstrate that the thiol-reactive, environmentally sensitive fluorogenic molecules 6-bromoacetyl-2-dimethylaminonaphthalene and 6-acryloyl-2-dimethylaminonaphthalene are substrates for glutathione transferases (GSTs). Product formation can be measured by strong increase in fluorescence of the glutathione conjugate. As these substances display a high nonenzymatic background reaction rate, we have synthesized and characterized 6-chloroacetyl-2-dimethylaminonaphthalene, which is less reactive, favoring the enzyme-catalyzed reaction. 6-Chloroacetyl-2-dimethylaminonaphthalene was found to be a substrate for all GSTs tested. Apparent k(cat)/K(m) values (ranging between 10 and 500 mM(-1)s(-1)) revealed a strong preference for soluble GSTP1-1, GSTA1-1, and activated MGST1. Thus, 6-chloroacetyl-2-dimethylaminonaphthalene can be used in a highly sensitive assay of these GSTs. 6-Acetyl-2-dimethylaminonaphthalene derivatives are very sensitive toward solvent polarity and potentially also toward properties of binding sites in proteins. Upon binding of the conjugate to GSTs the fluorescence intensity decreased and the emission maximum was blue-shifted. Therefore the interaction of the conjugate with GSTs can be characterized with regard to both binding affinity and kinetics by stopped-flow measurements, and 6-chloroacetyl-2-dimethylaminonaphthalene can be a valuable aid in mechanistic investigations of GSTs, especially those which possess low intrinsic fluorescence.

2-Naphthylamine↗
PubMed2005

Mosquito glutathione transferases.

The glutathione transferases (glutathione S-transferases, GSTs) are a diverse family of enzymes involved in a wide range of biological processes, many of which involve the conjugation of the tripeptide glutathione to an electrophilic substrate. Relatively little is known about the endogenous substrates of mosquito GSTs, and most studies have focused on their role in insecticide metabolism, because elevated levels of GST activity have been associated with resistance to all the major classes of insecticides. In addition, there is growing interest in the role of this enzyme family in maintaining the redox status of the mosquito cell, particularly in relation to vectorial capacity. Most GSTs are cytosolic dimeric proteins, although a smaller class of microsomal GSTs exists in insects, mammals, and plants. Each GST subunit has a G site that binds glutathione and a substrate-binding site or H site. There are more than 30 GST genes in mosquitoes. Additional diversity is contributed by alternative splicing to produce GSTs with differing substrate specificities. In this review, we first discuss the diversity of insect GST enzymes and their mode of action before focusing on the various functions that have been attributed to specific mosquito GSTs.

Alternative Splicing↗
PubMed2000

Plant glutathione S-transferases: enzymes with multiple functions in sickness and in health.

Glutathione S-transferases (GSTs) are abundant proteins encoded by a highly divergent, ancient gene family. Soluble GSTs form dimers, each subunit of which contains active sites that bind glutathione and hydrophobic ligands. Plant GSTs attach glutathione to electrophilic xenobiotics, which tags them for vacuolar sequestration. The role of GSTs in metabolism is unclear, although their complex regulation by environmental stimuli implies that they have important protective functions. Recent studies show that GSTs catalyse glutathione-depend-ent isomerizations and the reduction of toxic organic hydroperoxides. GSTs might also have non-catalytic roles as carriers for phytochemicals.

Catalysis↗