Browsing by Subject "Glutathione"
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Item Biological availability of selenium from sodium selenite, monoselenodiacetic acid, selenomethionine, and selenium yeast for glutathione peroxidase(Texas Tech University, 1980-05) Wang, Cheng ShengNot availableItem Engineering of de novo pathways for biosynthesis of glutathione analogues in Escherichia coli(2010-05) Veeravalli, Karthik; Georgiou, George; Molineux, Ian J.; Appling, Dean R.; Mullins, Charles B.; Maynard, JenniferThe low molecular weight (L.M.W.) thiol redox couple formed by γ-L-glutamyl-L-cysteinyl glycine, also called glutathione (reduced and oxidized), is present in most eukaryotes and a few species of bacteria. Glutathione plays a role in numerous cellular processes by providing a means of shuttling electrons to different enzymatic systems. As a result, thiol-dependent redox metabolic processes are highly coupled. Due to tight coupling of redox reactions, it is difficult to understand how changes in the concentration of glutathione would affect a specific glutathione-dependent process. Interestingly, only a small subset of bacteria encode the canonical enzyme for the biosynthesis of glutathione, namely γ-glutamyl cysteine synthetase (gshA gene product). The mechanisms by which glutathione-dependent processes are carried out in bacteria which do not have the genes for biosynthesis of glutathione or other L.M.W. thiols is not well understood. A genetic selection to restore a glutathione-dependent phenotype in E. coli, lacking the gene involved in first step of glutathione biosynthesis (gshA), was used to address how bacteria lacking gshA might substitute for glutathione. Genetic and biochemical analyses of the E. coli mutants isolated in the selection revealed a de novo pathway for biosynthesis of γ-glutamyl cysteine, the product formed normally by GshA. Additionally we found that the unnatural analogue of glutathione, γ-glutamyl homocysteine could also be formed by this pathway. Bioinformatic analysis suggested that bacteria lacking gshA may use these de novo pathways for biosynthesis of γ-glutamyl cysteine or γ-glutamyl homocysteine, which could serve as potential substitutes for glutathione. The engineering of de novo biosynthetic pathways for γ-glutamyl cysteine and γ-glutamyl homocysteine provided us a strategy for engineering a pathway for biosynthesis of another unnatural analogue of glutathione, β-aspartyl cysteine. Both γ-glutamyl homocysteine and β-aspartyl cysteine could potentially be used as orthologus redox couples in E. coli operating in parallel to glutathione to shuttle electrons to specific pathways which may thus be decoupled from glutathione availability. Glutathione-dependent enzymes that can use orthologous redox couples instead are biochemically isolated from network of other redox reactions in the cell and could be used to direct metabolic fluxes to specific pathways with high efficiencies. Towards this end, we show that glutathione transferase, a glutathione-dependent enzyme, can be engineered to use analogous thiols like γ-glutamyl cysteine as cofactors.Item Identification of methionine as a possible precursor to the selenocysteine catalytic site of glutathione peroxidase(Texas Tech University, 1985-12) Chung, Cha KwonNot availableItem In vitro hemolytic studies of selenium compounds and glutathione peroxidase and the effect of dietary selenium on resistance of mice to Klebsiella pneumoniae(Texas Tech University, 1983-05) Hu, Miao-linNot availableItem Investigating cellular responses to mutations in the glutathione and thioredoxin pathways of Escherichia coli(2009-12) Chrysostomou, Constantine; Georgiou, George; Isaac, SanchezInhibition of disulfide bond formation in Escherichia coli implicates an intricate collaboration of proteins which comprise the glutathione and thioredoxin reducing pathways. Bioengineers have successfully engineered E. coli possessing mutated reducing pathways that promote, rather than inhibit, disulfide bond formation in the cytoplasm. The transcriptome of six such mutant E. coli strains have been characterized using Microarray technology. We find that all mutant strains, exhibit a unique response to oxidative stress, not observed in wild type. Statistical analyses revealed the expression of more than 200 genes that are affected by mutations within the reducing pathways. Significantly up-regulated biological processes include cysteine biosynthesis, histidine biosynthesis, NADH Dehydrogenase I biosynthesis, sugar catabolic processes, and activation of stress responses . The second part of this work describes the construction of an E. coli strain that promotes the complete conversion of glutathione into its seemingly dormant derivative, glutathionylspermidine. This engineered strain can be used in assays designed to evaluate the effectiveness of glutathionylspermidine as a substitute for glutathione and, hopefully, allude to its true metabolic function.Item The effect of seaweed (Ascophyllum nodosum) extract on antioxidant activities and drought tolerance of tall fescue (Festuca arundinacea schreb.)(Texas Tech University, 1998-08) Ayad, Jamal YousefPlants have developed enzymatic and nonenzymatic antioxidant mechanisms to prevent oxidation of cellular compartments. Enhancing these mechanisms might help plants cope with encountered stresses. Greenhouse and field studies were conducted to examine the influence of seaweed(Ascophyllum nodosum) extract on antioxidant enzymes activities, forage growth, and persistence of tall fescue (Festuca arundinacea Schreb.). Furthermore, effects of soil moisture, plant genotype, and infection with the endophyte Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon and Hanlin) were investigated. In a greenhouse experiment, seaweed extract was applied to 'Martin' tall fescue at 0, 2, 4, 6, 8, and 10 kg ha^-1 in a randomized block design with four replicates. Seaweed extract linearly increased (P <0.05) glutathione reductase activity. Superoxide dismutase and ascorbate peroxidase were also increased but responses differed by time and treatment rates. In a second greenhouse experiment, seaweed extract was applied at 4 kg ha^-1 to endophyte-infected and non-infected 'Georgia Jessup' and 'KY-3r tall fescue grown with 50-100% and 30-100% field capacity soil moisture in a completely randomized design with four replications. Glutathione reductase activity increased (P < 0.05) in both genotypes in response to seaweed extract and moisture stress and tended to increase (P < 0.07) in response to the endophyte. Seaweed extract increased (P < 0.05) superoxide dismutase activity in both genotypes under water stress. Endophyte infected and non-infected KY-31 tall fescue were grown in a 2-yr field experiment, to investigate effects of 4 kg seaweed ha^-1 and three levels of irrigation to replace 0, 50,100% of potential evapotranspiration in a randomized block design with four replications. Superoxide dismutase, glutathione reductase, and ascorbate peroxidase activities were increased (P < 0.05) in response to seaweed extract, presence of the endophyte, and increased linearly (P < 0.05) in response to increased moisture stress. Plant growth and yield did not appear to be affected by seaweed extract at the applied rates. Results indicated that seaweed extract increased tall fescue antioxidant enzyme activities and may provide a tool for manipulating the antioxidant system in plants for increased protection against active oxygen species.Item The effects of dietary selenium, silver and methionine on glutathione peroxidase activity and cataracts in mice(Texas Tech University, 1985-05) Brigham, Dale EdwardNot available