99 research outputs found
Evidence for an NO-rebound, mechanism for production of N2O from nitrite by the copper-containing nitrite reductase from Achromobacter cycloclastes
AbstractReduction of NO−2 by the Cu-containing nitrite reductase from Achromobacter cycloclastes produces NO as the primary product initially, but as NO accumulates, NO production levels-off and N2O production becomes significant. Reaction of the enzyme with NO−2 in the presence of NO increases the amount of N2O product significantly, while trapping the NO product as nitrosylhemoglobin or rapid, removal of NO by sparging results in no detectable N2O production. Reaction of the enzyme with 15NO−2 in the presence of 14NO results in rapid formation of the mixed isotope product (14N, 15N)O in ca. 45% yield. In contrast, the presence or absence of NO has no effect on N2O production by a prototypical heme cd1-containing nitrite reductase. These results are consistent with formation of a labile Cu+−NO+ species in the copper enzyme, which normally decomposes to NO. Production of N2O requires that the released NO must rebind to the enzyme to combine with a second NO−2 or a species derived therefrom
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Complete Detoxification of Short Chain Chlorinated Aliphatic Compounds: Isolation of Halorespiring Organisms and Biochemical Studies of the Dehalogenating Enzyme Systems - Final Report
Work focused on the isolation and characterization of halorespiring populations, and the initial investigation of the dechlorinating enzyme systems. In addition, tools to evaluate the presence/activity to halorespiring populations in the environment were developed. The tools developed in this work (measurements of hydrogen consumption thresholds, molecular probes) are relevant for regulatory agencies in order to facilitate decisions on which bioremediation technology (biostimulation or bioaugmentation) is most promising at a particular site. In addition, a better understanding of the physiology of the halorespiring organisms as well as the biochemistry of the dehalogenating enzyme systems enhances our knowledge of how these organisms can successfully be employed in the bioremediation of contaminated sites
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Complete detoxification of short chain chlorinated aliphatic compounds: Isolation of halorespiring organisms and biochemical studies of the dehalogenating enzyme systems. 1998 annual progress report
'Widespread use and careless handling, storage and disposal practices, have lead to the dissemination of chlorinated short chain aliphatics into groundwater systems. These compounds are toxic and the presence of chlorinated ethenes and chlorinated propanes in the environment is of public concern. Halorespiration is a newly recognized anaerobic process by which certain bacteria use chlorinated compounds as terminal electron acceptors in their energy metabolism. In contrast to co-metabolic dechlorination, which is fortuitous, slow, and without benefit to the organisms, halorespiration, characterized by high dechlorination rates, is a specific metabolic process beneficial to the organism. The goals are to isolate and characterize organisms which use chlorinated ethenes (including tetrachloroethene [PCE], trichloroethene [TCE], cis-dichloroethene [cis-DCE], and vinyl chloride [VC], or 1,2-dichloropropane [1,2-D]) as electron acceptors in their energy metabolism. Better understanding of the physiology and phylogeny of the halorespiring organisms as well as the biochemistry of the dehalogenating enzyme systems, will greatly enhance the authors knowledge of how these organisms can successfully be employed in the bioremediation of contaminated sites. This report summarizes the results of 1.5 years of a 2-year project. Anaerobic microcosms were established using a variety of geographically distinct sediments. In several microcosms complete dechlorination of PCE to ethene (ETH), and 1,2-D to propene was observed. Upon subsequent transfers to anaerobic medium, four sediment-free, methanogenic enrichment cultures were obtained that dechlorinated PCE to ETH, and two cultures that dechlorinated 1,2-D to propene. 2-Bromoethanesulfonate (BES), a well known inhibitor of methanogens, did not inhibit the dechlorination of 1,2-D to propene or the dechlorination of PCE to cis-DCE. However, the complete dechlorination of PCE to VC and ETH was severely inhibited. They could also show that BES inhibited the dechlorination of chloroethenes in cultures without methanogens. Therefore, BES should not be used to attribute dechlorination activities to methanogens.
TEMPERATURE DEPENDENCE OF THE ELECTRON DRIFT MOBILITY IN HYDROGENATED a-Si PREPARED BY SPUTTERING
The temperature dependence of the electron drift mobility and its dispersion have been measured in sputtered a-SiHx films with different H contents. The data are consistent with the multiple trapping model of dispersive transport and demonstrate that the electron transport is insensitive to H content in the 14-19.5% range
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