Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.23.17 (PCE)
 1,301 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tetrachloroethene reductive dehalogenase from the tetrachloroethene-utilizing anaerobe, Dehalospirillum multivorans, was purified approximately 100-fold to apparent homogeneity. The purified dehalogenase catalyzed the reductive dechlorination of tetrachloroethene (PCE) to trichloroethene and of trichloroethene to cis-1,2-dichloroethene with reduced methyl viologen as the electron donor at a specific activity of 2.6 microkatal/mg. The apparent Km values for tetrachloroethene and trichloroethene were 0.20 and 0.24 mM, respectively. The apparent molecular mass of the native enzyme was determined by gel filtration to be 58 kDa. Sodium dodecyl sulfate-gel electrophoresis revealed a single protein band with a molecular mass of 57 kDa. One mol of dehalogenase contained 1.0 mol of corrinoid, 9.8 mol of iron, and 8.0 mol of acid-labile sulfur. The pH optimum was about 8.0. The enzyme had a temperature optimum of 42 degrees C. It was slightly oxygen-sensitive and was thermolabile above 50 degrees C. The dechlorination of PCE was stimulated by ammonium ions. Chlorinated methanes severely inhibited PCE dehalogenase activity.
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PMID:Purification and characterization of tetrachloroethene reductive dehalogenase from Dehalospirillum multivorans. 866 99

The membrane-associated tetrachloroethene reductive dehalogenase from the tetrachloroethene-reducing anaerobe, strain PCE-S, was purified 165-fold to apparent homogeneity in the presence of the detergent Triton X-100. The purified dehalogenase catalyzed the reductive dechlorination of tetrachloroethene to trichloroethene and of trichloroethene to cis-1,2-dichloroethene with reduced methyl viologen as the electron donor, showing a specific activity of 650 nkat/mg protein. The apparent Km values of the enzyme for tetrachloroethene, trichloroethene, and methyl viologen were 10 microM, 4 microM, and 0.3 mM, respectively. SDS-PAGE revealed a single protein band with an apparent molecular mass of 65 kDa. The apparent molecular mass of the native enzyme was 200 kDa as determined by gel filtration. Tetrachloroethene dehalogenase contained 0.7 +/- 0.3 mol corrinoid, 1.0 +/- 0.3 mol cobalt, 7.8 +/- 0.5 mol iron, and 10.3 +/- 2.0 mol acid-labile sulfur per mol subunit. The pH optimum was approximately 7.2, and the temperature optimum was approximately 50 degrees C. The dehalogenase was oxygen-sensitive with a half-life of approximately 50 min. The N-terminal amino acid sequence of the enzyme was determined, and no significant similarity was found to any part of the amino acid sequence of the tetrachloroethene (PCE) reductive dehalogenase from Dehalospirillum multivorans.
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PMID:Purification and characterization of the tetrachloroethene reductive dehalogenase of strain PCE-S. 957 35

Permeable reactive barriers (PRBs), such as the Waterloo Funnel and Gate System, first implemented at Canadian Forces Borden facility in 1992, are a passive remediation technology capable of controlling the migration of, and treating contaminated groundwater in situ. Most of the PRBs installed to date have been shallow installations created by backfilling sheet-pile shored excavations with iron filing reactive media. More recently continuous trenchers [R. Puls, Installation of permeable reactive barriers using continuous trenching equipment, Proceedings of the RTDF Permeable Barriers Work Group, Virginia Beach, VA, September 1997] and Caissons [J. Vogan, Caisson installation of a pilot scale, permeable reactive barrier in situ treatment zone at the Sommersworth Landfill, NH, Presented to the RTDF Permeable Barriers Work Group, Alexandria, VA, April 1996], and vertical fracturing emplacements [G. Hocking, Vertical hydraulic fracture emplacement of permeable reactive barriers, Progress Report delivered to the Permeable Reactive Barriers Workgroup of the Remedial Technology Development Forum, Beaverton, OR, April 1998] have been used to create reactive barriers in soil. None of the prior methods are capable of adequately addressing groundwater contamination in deep and fractured bedrock aquifers. The purpose of the RSF pilot study was to install reactive media into an impacted bedrock aquifer, and to evaluate the effectiveness of in situ treatment of chlorinated volatile organic compounds (CVOCs) and metals in that type of aquifer. Three discrete fractures were identified and treated and were subjected to testing before and after treatment. Between 300 and 1700 lb. of 1 mm diameter reactive proppants were injected into each zone to facilitate treatment. Monitoring data obtained from adjacent observation wells verified that fracking fluids reached at least 42 ft from the treatment well following hydrofracturing. The concentrations of many of the CVOCs decreased up to 98% based on the results of pre- and post-RSF treatment analyses. Consistent with other research, concentrations of CVOCs were noted to decrease including trichloroethene (TCE), tetrachloroethene (PCE), 1,1,1-trichloroethane (1,1,1-TCA), 1, 1-dichloroethane (1,1-DCA), and 1,1-dichloroethene (1,1-DCE) and increases were noted in concentrations of cis-1,2-dichloroethene (cis-1,2-DCE) and chloroform suggesting that the rate of transformation of the parent compounds to these daughter products is higher than the rate of destruction of the daughter products. The RSF pilot study demonstrated that: (1) zero valent iron foam proppants have the physical and chemical properties necessary to effectively treat CVOCs and metals in groundwater when inserted under high pressures into fractured bedrock. (2) Iron foam reactive media can be placed in bedrock using high pressure hydraulic fracturing equipment and polysaccharide viscosifiers. (3) The extent of the treatment can be monitored in situ using tracers and pressure transducers. (4) Well capacity is increased by improving hydraulic conductivity through hydraulic fracturing and proppant injection. The approximate cost of all of the effort expended in the pilot study was about US$200,000. Full-scale implementations are projected to cost between US$100,000 and US$1,000,000 and would depend on site specific conditions such as the extent and level of impacted groundwater requiring treatment. This technology can potentially be implemented to create treatment zones for the passive treatment of CVOC and metal impacted groundwater in fractured rock aquifers offering a cost-effective alternative to a pump and treat forever scenario.
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PMID:Results of the reactant sand-fracking pilot test and implications for the in situ remediation of chlorinated VOCs and metals in deep and fractured bedrock aquifers. 1051 68

The effects of surfactants, sodium dodecyl sulfate (SDS) and Triton X-a00 (TX), and alcohols (methanol, ethanol, and propanol) on the dehalogenation of TCE and PCE by zero-valent iron were examined. Surface concentrations of PCE and TCE on the iron were dependent on aqueous surfactant concentrations. At concentrations above the CMC, sorbed halocarbon concentrations declined and concentrations associated with solution phase micelles increased. The anionic surfactant SDS ([SDS] < CMC) did not affect reduction rates, until the CMC was exceeded after which reactivity decreased, possibly due to sequestering of the TCE and PCE in mobile micelles. The nonionic TX showed a mixed effect on reactivity, increasing the PCE reduction rate, but not affecting TCE removal. Production of TCE from PCE increased in the presence of TX. Similar experiments showed that methanol, ethanol, and propanol inhibited reduction of TCE and PCE by metallic iron. Zero-valent iron may be useful in recycling soil washing effluents contaminated with TCE and PCE.
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PMID:Effects of alcohols, anionic and nonionic surfactants on the reduction of PCE and TCE by zero-valent iron. 1131 92

Although the potential for KMnO4 to destroy chlorinated ethenes in situ was first recognized more than a decade ago, the geochemical processes that accompany the oxidation have not previously been examined. In this study, aqueous KMnO4 solutions (10-30 g/L) were injected into an unconfined sand aquifer contaminated by the dense non-aqueous-phase liquid (DNAPL) tetrachloroethylene (PCE). The effects of the injections were monitored using depth-specific, multilevel groundwater samplers, and continuous cores. Two distinct geochemical zones evolved within several days after injection. In one zone where DNAPL is present, reactions between KMnO4 and dissolved PCE resulted in the release of abundant chloride and hydrogen ions to the water. Calcite and dolomite dissolved, buffering the pH in the range of 5.8-6.5, releasing Ca, Mg, and CO2 to the pore water. In this zone, the aqueous Ca/Cl concentration ratio is close to 5:12, consistent with the following reaction for the oxidation of PCE in a carbonate-rich aquifer: 3C2Cl4 + 5CaCO3(s) + 4KMnO4 + 2H+ --> 11CO2 + 4MnO2(s) + H2O + 12Cl- + 5Ca2+ + 4K+. In addition to Mg from dolomite dissolution, increases in the concentration of Mg as well as Na may result from exchange with K at cation-exchange sites. In the second zone, where lesser amounts of PCE were present, KMnO4 persisted in the aquifer for more than 14 months, and the porewater pH increased graduallyto between 9 and 10 as a resultof reaction between KMnO4 and H2O. A small increase in SO4 concentrations in the zones invaded by KMnO4 suggests that KMnO4 injections caused oxidation of sulfide minerals. There are important benefits of carbonate mineral buffering during DNAPL remediation by in situ oxidation. In a carbonate-buffered system, Mn(VII) is reduced to Mn(IV) and is immobilized in the groundwater by precipitating as insoluble manganese oxide. Energy-dispersive X-ray spectroscopy analyses of the manganese oxide coatings on aquifer mineral grains have detected the impurities Al, Ca, Cl, Cu, Pb, P, K, Si, S, Ti, U, and Zn indicating that, similar to natural systems, precipitation of manganese oxide is accompanied by coprecipitation of other elements. In addition, the consumption of excess KMnO4 by reaction with reduced minerals such as magnetite will be minimized because the rates of these reactions increase with decreasing pH. Aquifer cores collected after the KMnO4 injections exhibit dark brown to black bands of manganese oxide reaction products in sand layers where DNAPL was originally present. Mineralogical investigations indicate that the manganese oxide coatings are uniformly distributed over the mineral grains. Observations of the coatings using transmission electron microscopy indicate that they are on the order of 1 microm thick, and consequently, the decrease in porosity through the formation of the coatings is negligible.
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PMID:Geochemical reactions resulting from in situ oxidation of PCE-DNAPL by KMnO4 in a sandy aquifer. 1134 43

The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.
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PMID:Evidence for simultaneous abiotic-biotic oxidations in a microbial-Fenton's system. 1147 49

The dissolved hydrogen concentrations under various redox processes were investigated based on batch experiments. Chloroethenes including tetrachloroethene (PCE), cis-dichloroethene (cis-DCE) and vinylchloride (VC) were respectively used as culture substrates. For each chloroethene, a series of bottles were prepared with the additions of different electron acceptors or donors such as nitrate, manganese oxide, ferrous iron, sulfate, carbondioxide and volatile fatty acids. Hydrogen concentrations as well as redox species were measured over time to ensure the achievements of characteristic hydrogen levels in various enrichment batches. The results showed that redox processes with nitrate, manganese oxide and ferric iron as the electron acceptors exhibited hydrogen threshold values close to PCE/TCE dechlorination, whereas cis-DCE and VC dechlorinations exhibited hydrogen threshold values in the range of sulfate reduction and methanogenesis, respectively. Characteristic hydrogen concentrations for various redox processes were as follows (nM): denitrification, 0.1-0.4; manganese reduction, 0.1-2.0; iron reduction, 0.1-0.4; sulfate reduction, 1.5-4.5; methanogenesis, 2.5-24; PCE/TCE dechlorination, 0.6-0.9; eis-DCE dechlorination, 0.1-2.5; and VC dechlorination, 2-24.
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PMID:Characteristic hydrogen concentrations for various redox processes in batch study. 1168 86

Chlorinated ethenes are pollutants in contaminated soil and groundwater, and one of the efficient way to remove them is biodegradation. In this paper, the microbial breakdown of PCE, cis-DCE and VC with initial concentrations of 100 mumol/L were studied under different redox conditions at temperature 20 degrees C. The results showed that in the presence of ferric iron and carbon dioxide, PCE were dechlorinated to TCE (0.26/day) and cis-DCE (0.31/day), respectively. In the presence of fatty acids and without competition from inorganic electron acceptors, all the studied chlorinated compounds were completely dechlorinated to ethenes. However, the degradation rates of cis-DCE and VC (0.04/day) were much lower than that of PCE (0.57/day). Under denitrifying, manganese reducing and sulfate reducing conditions, no degradation of chloroethenes was observed. When the temperature was lowered to 12 degrees C, the activities of dechlorinating microbes were also reduced, nevertheless, the completely reductive dechlorination of chloroethenes still occurred.
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PMID:[Dechlorination of chlorinated ethenes under different redox conditions]. 1204 14

The sorption of benzo[a]pyrene (BaP) to sediment contaminated by acid mine drainage from the River Carnon, SW England, has been studied as a function of particle concentration in river water and seawater. The sediment is iron-rich and has a high specific surface area, and previous studies have demonstrated that it exhibits positive surface charge when suspended in native river water (pH approximately 5), and, through an increase in pH (to about 8) and the adsorption of organic matter, negative charge when suspended in seawater. Unit sorption of BaP exhibited an inverse dependency on particle concentration (particle concentration effect. PCE) in seawater, but was relatively invariant in river water. Consequently, BaP was apparently salted out at particle concentrations below about 100 mg l(-1), and salted in at higher particle concentrations. The absence of a PCE (and inherent salting in) for such a hydrophobic compound is an unusual, and possibly unique observation, and is inconsistent with a third (e.g. colloidal) phase model. More likely, a PCE in seawater is caused, in part, by salt induced particle-particle or particle-organic matter interactions which result in increasing particle aggregation or sorption irreversibility with increasing particle concentration. Although the results have limited environmental application and do not conclusively resolve any causal mechanisms for the PCE, they suggest that, with respect to neutral organic compounds, adsorbed organic matter is a pre-requisite for a PCE in the natural environment, and the effect should not solely or generally be attributed to the existence of a third phase.
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PMID:Sorption of benzo[a]pyrene to sediment contaminated by acid mine drainage: contrasting particle concentration-dependencies in river water and seawater. 1209 76

Short-term experiments were conducted to investigate the effect of a commercial Fe and an iron-bearing clay mineral, ferruginuous smectite (SWa-1), on the degradation of pentachloroethane (PCA). After 3 h of contact time, SWa-1 catalyzed PCA dehydrochlorination to tetrachloroethene (PCE, 65% conversion), whereas commercial Fe promoted PCA stepwise dechlorination via dehydrochlorination (approximately 40% conversion) and subsequent PCE hydrogenolysis to trichloroethene (TCE). The addition of unaltered SWa-1 to commercial Fe led to a complete inhibition on TCE production, whereas the addition of reduced SWa-1 barely resulted in a 30% decrease.
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PMID:Dechlorination of pentachloroethane by commercial Fe and ferruginous smectite. 1210 4


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