Browsing by Subject "Redox"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Disulfide dithiol redox titrations of proteins(2005-05) Mason, Jeremy Todd; Knaff, David B.; Pare, PaulRedox-active disulfide/dithiol couples in proteins play important regulatory roles within cells. Disulfide/dithiol redox reactions of regulatory proteins found in the purple photosynthetic bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus are used to regulate the expression of genes encoding photosystem components in response to the presence oxygen and light. Disulfide/dithiol redox reactions of regulatory proteins found in the yeast Saccharomyces cerevisiae regulate expression of genes encoding the production of peroxide-scavenging proteins in response to intracellular H2O2 tension. AppA and PpsR are two proteins present in R. sphaeroides that have been shown to regulate gene expression in response to oxygen through disulfide/dithiol redox chemistry. AppA, which contains FAD, also functions as a blue light receptor. It has been proposed that AppA reduces PpsR, causing PpsR to lose its abililty to bind DNA and repress transcription of photosynthesis genes. Redox titrations of the disulfide/dithiol couples in PpsR and AppA were carried out at pH 7.0 and the two proteins were shown to be isopotential, with both having Em values of -320 mV at pH 7.0. Em vs. pH profiles for PpsR and RegB, a protein involved in regulation of gene expression in R. capsulatus, were generated in an attempt to detect pKa values for groups involved in proton uptake/release that is coupled to the disulfide/dithiol redox chemistry. However, neither protein showed a pKa for redox-linked residues at physiological pH values. Yap1 is a key regulator of gene expression in S. cerevisiae in response to peroxides. Gpx3 and Trx2 are two additional components of this S. cerevisiae regulatory cascade. Em values for the two disulfide bonds in Yap1 have been determined (Em1 = -330 mV and Em2 = -155 mV), as has an Em value of -315 mV for Gpx3, a component thought to serve as the physiological oxidant for Yap1. Trx2 has an Em of -275 mV, which is capable of reducing the disulfide in Yap1 that corresponds to Em2, but not Em1.Item Disulfide/Dithiol redox titrations of proteins(Texas Tech University, 2005-05) Mason, Jeremy Todd; Knaff, David B.; Pare, PaulRedox-active disulfide/dithiol couples in proteins play important regulatory roles within cells. Disulfide/dithiol redox reactions of regulatory proteins found in the purple photosynthetic bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus are used to regulate the expression of genes encoding photosystem components in response to the presence oxygen and light. Disulfide/dithiol redox reactions of regulatory proteins found in the yeast Saccharomyces cerevisiae regulate expression of genes encoding the production of peroxide-scavenging proteins in response to intracellular H2O2 tension. AppA and PpsR are two proteins present in R. sphaeroides that have been shown to regulate gene expression in response to oxygen through disulfide/dithiol redox chemistry. AppA, which contains FAD, also functions as a blue light receptor. It has been proposed that AppA reduces PpsR, causing PpsR to lose its abililty to bind DNA and repress transcription of photosynthesis genes. Redox titrations of the disulfide/dithiol couples in PpsR and AppA were carried out at pH 7.0 and the two proteins were shown to be isopotential, with both having Em values of -320 mV at pH 7.0. Em vs. pH profiles for PpsR and RegB, a protein involved in regulation of gene expression in R. capsulatus, were generated in an attempt to detect pKa values for groups involved in proton uptake/release that is coupled to the disulfide/dithiol redox chemistry. However, neither protein showed a pKa for redox-linked residues at physiological pH values. Yap1 is a key regulator of gene expression in S. cerevisiae in response to peroxides. Gpx3 and Trx2 are two additional components of this S. cerevisiae regulatory cascade. Em values for the two disulfide bonds in Yap1 have been determined (Em1 = -330 mV and Em2 = -155 mV), as has an Em value of -315 mV for Gpx3, a component thought to serve as the physiological oxidant for Yap1. Trx2 has an Em of -275 mV, which is capable of reducing the disulfide in Yap1 that corresponds to Em2, but not Em1.Item Geochemical effects of elevated methane and carbon dioxide in near-surface sediments above an EOR/CCUS site(2013-05) Hingst, Mary Catherine; Young, Michael H.; Romanak, Katherine DunckerCarbon capture, utilization and storage (CCUS) aims to reduce CO₂ emissions by capturing CO₂ from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO₂ and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells. We hypothesize that CO₂ and CH₄ migration into the vadose zone and subsequent O₂ dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO₂ and CH₄ and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH₄ (45%) from depth reaches the surface and oxidizes to CO₂ (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO₂ and CH₄ concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O₂, <1% CO₂, 0% CH₄) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O₂, 0.1-5% CO₂, <0.1% CH₄) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O₂ (r = 0.95), pH and CO₂ (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (<2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO₂/CH₄. Conclusions are: 1) oxidation of CH₄ to CO₂ depletes O₂ causing reducing conditions; 2) high CO₂ and low O₂ affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO₂, CH₄ and O₂) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment.Item PAH degradation and redox control in an electrode enhanced sediment cap(2012-08) Yan, Fei, Ph. D.; Reible, Danny D.; Bennett, Philip; Charbeneau, Randall; Gilbert, Robert; Liljestrand, HowardCapping is typically used to control contaminant release from the underlying sediments. However, the presence of conventional caps often eliminates or slows natural degradation that might otherwise occur at the surface sediment. This is primarily due to the development of reducing conditions within the sediment that discourage hydrocarbon degradation. The objective of this study was to develop a novel active capping method, an electrode enhanced cap, to manipulate the redox potential to produce conditions more favorable for hydrocarbon degradation and evaluate the approach for the remediation of PAH contaminated sediment. A preliminary study of electrode enhanced biodegradation of PAH in sediment slurries showed that naphthalene and phenanthrene concentration decreased significantly within 4 days, and PAH degrading genes increased by almost 2 orders of magnitude. In a sediment microcosm more representative of expected field conditions, graphite cloth was used to form an anode at the sediment-cap interface and a similar cathode was placed a few centimeters above within a thin sand layer. With the application of 2V voltage, ORP increased and pH dropped around the anode reflecting water electrolysis. Various cap amendments (buffers) were employed to moderate pH changes. Bicarbonate was found to be the most effective in laboratory experiments but a slower dissolving buffer, e.g. siderite, may be more effective under field conditions. Phenanthrene concentration was found to decrease slowly with time in the vicinity of the anode. In the sediment at 0-1 cm below the anode, phenanthrene concentrations decreased to ~70% of initial concentration with no bicarbonate, and to ~50% with bicarbonate over ~70 days, whereas those in the control remained relatively constant. PAH degrading gene increased compared with control, providing microbial evidence of PAH biodegradation. A voltage-current relationship, which incorporated separation distance and the area of the electrodes, was established to predict current. A coupled reactive transport model was developed to simulate pH profiles and model results showed that pH is neutralized at the anode with upflowing groundwater seepage. This study demonstrated that electrode enhanced capping can be used to control redox potential in a sediment cap, provide microbial electron acceptors, and stimulate PAH degradation.