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Reductive Pathways (reductive + pathway)
Selected AbstractsTransformation of 2,4,6-trinitrotoluene in soil in the presence of the earthworm Eisenia andrei,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2000Agnčs Y. Renoux Abstract The ability of the earthworm Eisenia andrei to metabolize 2,4,6-trinitrotoluene (TNT) was studied in experiments with TNT-spiked soils, dermal contact tests, and with an in vitro assay. Lethality of TNT in a forest sandy soil was first determined (14-d LC50 = 143 mg/kg). Then TNT at lethal and sublethal concentrations was applied to the same soil and was monitored along with its metabolites in extracts of soil and earthworm tissue for up to 14 d postapplication. High performance liquid chromatography-ultra violet analyses indicated that TNT was transformed in the presence of E. andrei by a reductive pathway to 2-amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), 2,4-diamino-6-nitrotoluene (2,4-DANT), and traces of 2,6-di-amino-4-nitrotoluene (2,6-DANT) in earthworm tissues. This transformation could be explained by either a metabolic mechanism within the earthworm or by the enhancement of an earthworm-associated microbial activity or both. The TNT concentrations decreased from the spiked soils. However, the monoamino-dinitrotoluene (2-ADNT and 4-ADNT) concentrations increased with exposure duration and were dependent on the initial TNT soil concentrations. This was also observed to a lesser extent in the TNT-spiked soils with no earthworms present. The biotransformation of TNT into 2-ADNT, 4-ADNT, and 2,4-DANT and the presence of these metabolites in E. andrei after dermal contact on TNT-spiked filter paper showed that dermal uptake can be a significant exposure route for TNT. In vitro experiments showed that earthworm homogenate could metabolize TNT and form 2-ADNT and 4-ADNT at room temperature and at 37°C. This effect was inhibited by heat inactivation prior to incubation or by incubation at 4°C, suggesting that the biotransformation of TNT in the presence of E. andrei may be enzymatic in nature. [source] Crystallization and preliminary crystallographic studies of the recombinant dihydropyrimidinase from Sinorhizobium meliloti CECT4114ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2006Sergio Martínez-Rodríguez Dihydropyrimidinases are involved in the reductive pathway of pyrimidine degradation, catalysing the hydrolysis of 5,6-dihydrouracil and 5,6-dihydrothymine to the corresponding N -carbamoyl ,-amino acids. This enzyme has often been referred to as hydantoinase owing to its industrial application in the production of optically pure amino acids starting from racemic mixtures of 5-monosubstituted hydantoins. Recombinant dihydropyrimidinase from Sinorhizobium meliloti CECT4114 (SmelDhp) has been expressed, purified and crystallized. Crystallization was performed using the counter-diffusion method with capillaries of 0.3,mm inner diameter. Crystals of SmelDhp suitable for data collection and structure determination were grown in the presence of agarose at 0.1%(w/v) in order to ensure mass transport controlled by diffusion. X-ray data were collected to a resolution of 1.85,Ĺ. The crystal belongs to the orthorhombic space group C2221, with unit-cell parameters a = 124.89, b = 126.28, c = 196.10,Ĺ and two molecules in the asymmetric unit. A molecular-replacement solution has been determined and refinement is in progress. [source] Simulation study of methemoglobin reduction in erythrocytesFEBS JOURNAL, Issue 6 2007Differential contributions of two pathways to tolerance to oxidative stress Methemoglobin (metHb), an oxidized form of hemoglobin, is unable to bind and carry oxygen. Erythrocytes are continuously subjected to oxidative stress and nitrite exposure, which results in the spontaneous formation of metHb. To avoid the accumulation of metHb, reductive pathways mediated by cytochrome b5 or flavin, coupled with NADH-dependent or NADPH-dependent metHb reductases, respectively, keep the level of metHb in erythrocytes at less than 1% of the total hemoglobin under normal conditions. In this work, a mathematical model has been developed to quantitatively assess the relative contributions of the two major metHb-reducing pathways, taking into consideration the supply of NADH and NADPH from central energy metabolism. The results of the simulation experiments suggest that these pathways have different roles in the reduction of metHb; one has a high response rate to hemoglobin oxidation with a limited reducing flux, and the other has a low response rate with a high capacity flux. On the basis of the results of our model, under normal oxidative conditions, the NADPH-dependent system, the physiological role of which to date has been unclear, is predicted to be responsible for most of the reduction of metHb. In contrast, the cytochrome b5,NADH pathway becomes dominant under conditions of excess metHb accumulation, only after the capacity of the flavin,NADPH pathway has reached its limit. We discuss the potential implications of a system designed with two metHb-reducing pathways in human erythrocytes. [source] The metabolic role and evolution of l -arabinitol 4-dehydrogenase of Hypocrea jecorinaFEBS JOURNAL, Issue 10 2004Manuela Pail l -Arabinitol 4-dehydrogenase (Lad1) of the cellulolytic and hemicellulolytic fungus Hypocrea jecorina (anamorph: Trichoderma reesei) has been implicated in the catabolism of l -arabinose, and genetic evidence also shows that it is involved in the catabolism of d -xylose in xylitol dehydrogenase (xdh1) mutants and of d -galactose in galactokinase (gal1) mutants of H. jecorina. In order to identify the substrate specificity of Lad1, we have recombinantly produced the enzyme in Escherichia coli and purified it to physical homogeneity. The resulting enzyme preparation catalyzed the oxidation of pentitols (l -arabinitol) and hexitols (d -allitol, d -sorbitol, l -iditol, l -mannitol) to the same corresponding ketoses as mammalian sorbitol dehydrogenase (SDH), albeit with different catalytic efficacies, showing highest kcat/Km for l -arabinitol. However, it oxidized galactitol and d -talitol at C4 exclusively, yielding l -xylo-3-hexulose and d -arabino-3-hexulose, respectively. Phylogenetic analysis of Lad1 showed that it is a member of a terminal clade of putative fungal arabinitol dehydrogenase orthologues which separated during evolution of SDHs. Juxtapositioning of the Lad1 3D structure over that of SDH revealed major amino acid exchanges at topologies flanking the binding pocket for d -sorbitol. A lad1 gene disruptant was almost unable to grow on l -arabinose, grew extremely weakly on l -arabinitol, d -talitol and galactitol, showed reduced growth on d -sorbitol and d -galactose and a slightly reduced growth on d -glucose. The weak growth on l -arabinitol was completely eliminated in a mutant in which the xdh1 gene had also been disrupted. These data show not only that Lad1 is indeed essential for the catabolism of l -arabinose, but also that it constitutes an essential step in the catabolism of several hexoses; this emphasizes the importance of such reductive pathways of catabolism in fungi. [source] Protein disulfide bond generation in Escherichia coli DsbB,DsbAJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2008Kenji Inaba Protein disulfide bond formation is catalyzed by a series of Dsb enzymes present in the periplasm of Escherichia coli. The crystal structure of the DsbB,DsbA,ubiquinone ternary complex provided important insights into mechanisms of the de novo disulfide bond generation cooperated by DsbB and ubiquinone and of the disulfide bond shuttle from DsbB to DsbA. The structural basis for prevention of the crosstalk between the DsbA,DsbB oxidative and the DsbC,DsbD reductive pathways has also been proposed. [source] Pathways of Change: Organizations in TransitionPUBLIC ADMINISTRATION, Issue 1 2006Ljiljana Erakovic This article discusses and illustrates organizational changes as initiated by ownership transition. It develops and elaborates three different pathways that organizations might follow through the process of transformation from government departments to state-owned enterprises, and then to privately-owned companies: the incremental, radical and reductive pathways. The research reported here is based on 11 case studies of New Zealand privatized companies. The pathway approach develops and extends existing models of transitional organizational trajectories, emphasizing the importance of antecedent conditions of organizational development, current environmental patterns and the strategic choices of the government and new owners. [source] Treatment of an explosives plume in groundwater using an organic mulch biowallREMEDIATION, Issue 1 2009Farrukh Ahmad A field demonstration of a mulch permeable reactive barrier (PRB), or "biowall," as an in situ treatment technology for explosives in groundwater is summarized. Organic mulch consists of insoluble carbon biopolymers that are enzymatically hydrolyzed during decomposition to release aqueous total organic carbon (TOC). The released TOC is then available for microorganisms to use as an electron donor to transform electrophilic contaminants via reductive pathways. A 100-foot-long and 2-foot-thick mulch biowall was installed at the Pueblo Chemical Army Depot in Colorado to treat a shallow groundwater plume containing hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). To discourage groundwater flow bypassing around and under the biowall in this highly permeable formation, a hydraulic control was installed and the PRB was keyed into the bedrock. Technology performance was monitored using a monitoring well network to establish the development and extent of the downgradient treatment zone. Performance objectives of the field demonstration were: (1) greater than 90 percent removal of RDX across the PRB and the treatment zone; (2) an RDX concentration of less than 0.55 ,g/L in the treatment zone; and (3) cumulative toxic intermediate concentration (nitroso intermediates of RDX, MNX, DNX, and TNX) of less than 20 percent of the upgradient RDX concentration. All performance objectives were met within seven months after installation once the system reached a pseudo-steady state. By this point, a sustained reducing/treatment zone had been created downgradient of the mulch PRB that showed greater than 93 percent RDX removal, RDX concentrations less than 0.55 ,g/L, and no accumulation of toxic intermediates. The mulch biowall implemented during this demonstration was successful at meeting performance objectives while addressing the majority of potential concerns of the technology. © 2009 Wiley Periodicals, Inc. [source] Considerations for the design of organic mulch permeable reactive barriersREMEDIATION, Issue 1 2007Farrukh Ahmad Organic mulch consists of insoluble carbon biopolymers that are enzymatically hydrolyzed during decomposition to release aqueous total organic carbon (TOC). The released TOC is utilized by microorganisms as an electron donor to transform electrophilic contaminants via reductive pathways. Over the last decade, organic mulch permeable reactive barriers (PRBs), or biowalls, have received increased interest as a relatively inexpensive slow-release electron donor technology for addressing contaminated groundwater. To date, biowalls have been installed to enhance the passive bioremediation of groundwater contaminated with a variety of electrophilic compounds, including chlorinated solvents, explosives, and perchlorate. In addition, several mulch biowall projects are currently under way at several U.S. Department of Defense facilities. However, at the present time, the guidelines available for the design of mulch PRBs are limited to a few case studies published in the technical literature. A biowall design, construction, and operation protocol document is expected to be issued by the Air Force Center for Environmental Excellence in 2007. In this publication, three technical considerations that can have a significant impact on the design and performance of mulch PRBs are presented and discussed. These technical considerations are: (1) hydraulic characteristics of the mulch bed; (2) biochemical characteristics of different types of organic amendments used as mulch PRB fill materials; and (3) a transport model that can be used to estimate the required PRB thickness to attain cleanup standards. © 2007 Wiley Periodicals, Inc. [source] | ||||||||||