Author
David J. Pulford
Bio: David J. Pulford is an academic researcher from University of Dundee. The author has contributed to research in topics: Glutathione S-transferase & Glutathione. The author has an hindex of 7, co-authored 7 publications receiving 3767 citations.
Papers
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TL;DR: The biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress, and to allow identification of factors that may modulate resistance to specific noxious chemicals.
Abstract: The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...
3,516 citations
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Abstract: The cDNA encoding human glutathione S-transferase (GST) T1 has been expressed as two recombinant forms in Escherichia coli that could be purified by affinity chromatography on either IgG-Sepharose or nickel-agarose; one form of the transferase was synthesized from the pALP 1 expression vector as a Staphylococcus aureus protein A fusion, whereas the other form was synthesized from the pET-20b expression vector as a C-terminal polyhistidine-tagged recombinant. The yields of the two purified recombinant proteins from E. coli cultures were approx. 15 mg/l for the protein A fusion and 25 mg/l for the C-terminal polyhistidine-tagged GST T1-1. The purified recombinant proteins were catalytically active, although the protein A fusion was typically only 5-30% as active as the histidine-tagged GST. Both recombinant forms could catalyse the conjugation of glutathione with the model substrates 1,2-epoxy-3-(4'-nitrophenoxy)propane,4-nitrobenzyl chloride and 4-nitrophenethyl bromide but were inactive towards 1-chloro-2,4-dinitrobenzene, ethacrynic acid and 1-menaphthyl sulphate. Recombinant human GST T1-1 was found to exhibit glutathione peroxidase activity and could catalyse the reduction of cumene hydroperoxide. In addition, recombinant human GST T1-1 was found to conjugate glutathione with dichloromethane, a pulmonary and hepatic carcinogen in the mouse. Immunoblotting with antibodies raised against different transferase isoenzymes showed that GST T1-1 is expressed in a large number of human organs in a tissue-specific fashion that differs from the pattern of expression of classes Alpha, Mu and Pi GST. Most significantly, GST T1-1 was found in only low levels in human pulmonary soluble extract of cells, suggesting that in man the lung has little capacity to activate the volatile dichloromethane.
144 citations
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TL;DR: Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases, and a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin is identified.
97 citations
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TL;DR: Computer-assisted analysis of the upstream sequence has indicated the presence of an antioxidant-responsive element (ARE), and several elements thought to be required for tissue-specific expression of the enzyme, in both upstream and intronic sequences.
Abstract: We have isolated and characterized genomic DNA encoding the rat glutathione S-transferase Yc 2 subunit. This protein is now referred to as rGSTA5 and is noteworthy because of its high activity towards aflatoxin B 1 -8,9-epoxide, its marked inducibility by chemoprotectors, its sex-specific regulation, and its overexpression in hepatoma and preneoplastic nodules. The rGSTA5 gene, which was isolated on two overlapping bacteriophage λ clones, is approx. 12 kb in length and, unlike other class Alpha genes described to date, it comprises six exons. The transcription start site has been identified 228 bp upstream from the ATG translational initiation codon, and is situated 51 bp downstream from a consensus TATA-box. Deletion analysis, using luciferase reporter constructs, has shown that the region between -177 bp and +65 bp from the transcriptional start site contains a functional promoter. Computer-assisted analysis of the upstream sequence has indicated the presence of an antioxidant-responsive element (ARE), and several elements thought to be required for tissue-specific expression of the enzyme. In addition, several putative oestrogen-responsive half sites were observed in both upstream and intronic sequences.
37 citations
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TL;DR: A novel gene fusion approach which may be of more general use has been developed for investigating the function of calmodulin in the budding yeast Saccharomyces cerevisiae by fusing a portion of the Staphylococcus aureus spa gene (encoding protein A) to CMD1, which generates a yeast cal modulin with an affinity tag able to bind immunoglobulins.
Abstract: Summary
A novel gene fusion approach which may be of more general use has been developed for investigating the function of calmodulin in the budding yeast Saccharomyces cerevisiae. By fusing a portion of the Staphylococcus aureus spa gene (encoding protein A) to CMD1, the S. cerevisiae gene encoding calmodulin, we have generated a yeast calmodulin with an affinity tag able to bind immunoglobulins. The chimaeric protein A–calmodulin (ProtA–CaM) polypeptide functions in vivo and shows Ca2+-dependent binding to calmodulin target proteins. The spa–CMD1 fusion has been used (i) to prepare (by affinity chromatography) a fraction of yeast proteins which interact with calmodulin, (ii) to isolate genes encoding calmodulin target proteins by direct screening of an expression library, and (iii) to visualize calmodulin-binding proteins in crude extracts by Western blot analysis.
31 citations
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TL;DR: This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process and the role of enzymatic and non-enzymatic antioxidants in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors.
5,937 citations
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TL;DR: There is little doubt that measurements of bioaccumulation and biomarker responses in fish from contaminated sites offer great promises for providing information that can contribute to environmental monitoring programs designed for various aspects of ERA.
4,397 citations
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TL;DR: In this review, the cellular oxidant and antioxidant systems are summarized and the cellular effects and mechanisms of the oxidative stress are discussed.
3,573 citations
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TL;DR: It is postulate that Keap1 and Nrf2 constitute a crucial cellular sensor for oxidative stress, and together mediate a key step in the signaling pathway that leads to transcriptional activation by this novel NRF2 nuclear shuttling mechanism.
Abstract: Transcription factor Nrf2 is essential for the antioxidant responsive element (ARE)-mediated induction of phase II detoxifying and oxidative stress enzyme genes. Detailed analysis of differential Nrf2 activity displayed in transfected cell lines ultimately led to the identification of a new protein, which we named Keap1, that suppresses Nrf2 transcriptional activity by specific binding to its evolutionarily conserved amino-terminal regulatory domain. The closest homolog of Keap1 is a Drosophila actin-binding protein called Kelch, implying that Keap1 might be a Nrf2 cytoplasmic effector. We then showed that electrophilic agents antagonize Keap1 inhibition of Nrf2 activity in vivo, allowing Nrf2 to traverse from the cytoplasm to the nucleus and potentiate the ARE response. We postulate that Keap1 and Nrf2 constitute a crucial cellular sensor for oxidative stress, and together mediate a key step in the signaling pathway that leads to transcriptional activation by this novel Nrf2 nuclear shuttling mechanism. The activation of Nrf2 leads in turn to the induction of phase II enzyme and antioxidative stress genes in response to electrophiles and reactive oxygen species.
3,166 citations
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TL;DR: The strategy of using food additives to protect farm animals from the toxin may also provide effective and economical new approaches to protecting human populations.
1,624 citations