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101.
Performance of inverse anaerobic fluidized bed reactor for treating high strength organic wastewater during start-up phase 总被引:2,自引:0,他引:2
The aim of this work is to report on the physical characteristics of carrier material (perlite), biomass growth on the carrier material and the biogas production during an apparent steady state period in an inverse anaerobic fluidized bed reactor (IAFBR) for treating high strength organic wastewater. Before starting up the reactor, physical properties of the carrier material were determined. One millimeter diameter perlite particle is found to have a wet specific density of 295 kg/m(3) with specific surface area of 7.010 m(2)/g. This material has provided a good surface for biomass attachment and development. The biofilm concentration (in terms of attached volatile solids (AVS)) attached to carrier material was found to be 0.66 g(AVS)/g(solid). Most particles have been covered with a thin biofilm of uniform thickness. Once the inverse anaerobic fluidized bed system reached the steady state, the organic load was increased step wise by reducing hydraulic retention time (HRT) from 2 days to 0.16 day, while maintaining the constant feed of chemical oxygen demand (COD) concentration. This system has achieved 84% COD removal and reached the biogas production of 13.22 l/l/d at an organic loading rate (OLR) of 35 kgCOD/m(3)/d. 相似文献
102.
Saccharomyces cerevisiae expresses a 67.8 kDa homodimeric serine thioesterase, S-formylglutathione hydrolase (SFGH), that is 39.9% identical with human esterase D. Both enzymes possess significant carboxylesterase and S-formylglutathione thioesterase activity but are unusually resistant to organophosphate (OP) inhibitors. We determined the X-ray crystal structure of yeast (y) SFGH to 2.3 A resolution by multiwavelength anomalous dispersion and used the structure to guide site-specific mutagenesis experiments addressing substrate and inhibitor reactivity. Our results demonstrate a steric mechanism of OP resistance mediated by a single indole ring (W197) located in an enzyme "acyl pocket". The W197I substitution enhances ySFGH reactivity with paraoxon by >1000-fold ( k i (W197I) = 16 +/- 2 mM (-1) h (-1)), thereby overcoming natural OP resistance. W197I increases the rate of OP inhibition under pseudo-first-order conditions but does not accelerate OP hydrolysis. The structure of the paraoxon-inhibited W197I variant was determined by molecular replacement (2.2 A); it revealed a stabilized sulfenic acid at Cys60. Wild-type (WT) ySFGH is inhibited by thiol reactive compounds and is sensitive to oxidation; thus, the cysteine sulfenic acid may play a role in the regulation of a "D-type" esterase. The structure of the W197I variant is the first reported cysteine sulfenic acid in a serine esterase. We constructed five Cys60/W197I variants and show that introducing a positive charge near the oxyanion hole, W197I/C60R or W197I/C60K, results in a further enhancement of the rates of phosphorylation with paraoxon ( k i = 42 or 80 mM (-1) h (-1), respectively) but does not affect the dephosphorylation of the enzyme. We also characterized three histidine substitutions near the oxyanion hole, G57H, L58H, and M162H, which significantly decrease esterase activity. 相似文献
103.
Imidazolonepropionase (HutI) (imidazolone-5-propanote hydrolase, EC 3.5.2.7) is a member of the amidohydrolase superfamily and catalyzes the conversion of imidazolone-5-propanoate to N-formimino-L-glutamate in the histidine degradation pathway. We have determined the three-dimensional crystal structures of HutI from Agrobacterium tumefaciens (At-HutI) and an environmental sample from the Sargasso Sea Ocean Going Survey (Es-HutI) bound to the product [ N-formimino-L-glutamate (NIG)] and an inhibitor [3-(2,5-dioxoimidazolidin-4-yl)propionic acid (DIP)], respectively. In both structures, the active site is contained within each monomer, and its organization displays the landmark feature of the amidohydrolase superfamily, showing a metal ligand (iron), four histidines, and one aspartic acid. A catalytic mechanism involving His265 is proposed on the basis of the inhibitor-bound structure. This mechanism is applicable to all HutI forms. 相似文献
104.
Brca2 (XRCC11) Deficiency Results in Radioresistant DNA Synthesis and a Higher Frequency of Spontaneous Deletions 总被引:1,自引:0,他引:1 下载免费PDF全文
Maria Kraakman-van der Zwet Wilhelmina J. I. Overkamp Rebecca E. E. van Lange Jeroen Essers Annemarie van Duijn-Goedhart Ingrid Wiggers Srividya Swaminathan Paul P. W. van Buul Abdellatif Errami Raoul T. L. Tan Nicolaas G. J. Jaspers Shyam K. Sharan Roland Kanaar Magorzata Z. Zdzienicka 《Molecular and cellular biology》2002,22(2):669-679
We show here that the radiosensitive Chinese hamster cell mutant (V-C8) of group XRCC11 is defective in the breast cancer susceptibility gene Brca2. The very complex phenotype of V-C8 cells is complemented by a single human chromosome 13 providing the BRCA2 gene, as well as by the murine Brca2 gene. The Brca2 deficiency in V-C8 cells causes hypersensitivity to various DNA-damaging agents with an extreme sensitivity toward interstrand DNA cross-linking agents. Furthermore, V-C8 cells show radioresistant DNA synthesis after ionizing radiation, suggesting that Brca2 deficiency affects cell cycle checkpoint regulation. In addition, V-C8 cells display tremendous chromosomal instability and a high frequency of abnormal centrosomes. The mutation spectrum at the hprt locus showed that the majority of spontaneous mutations in V-C8 cells are deletions, in contrast to wild-type V79 cells. A mechanistic explanation for the genome instability phenotype of Brca2-deficient cells is provided by the observation that the nuclear localization of the central DNA repair protein in homologous recombination, Rad51, is reduced in V-C8 cells. 相似文献
105.
Swaminathan Palanisami Krishna Kannan Uma Lakshmanan 《Journal of applied phycology》2012,24(5):1093-1098
The marine cyanobacterium Phormidium valderianum BDU 140441 exhibited the ability to grow at 0.25?mM tannic acid, a known hindering chemical for microbial growth. The tannic acid-degrading ability of the organism is evident from the UV–visible absorption spectrum. In addition, the existence of tannase has been localized by activity staining, and its induction in activity upon tannic acid exposure was confirmed in native gel. The critical tannic acid metabolization enzymes tested for are polyphenol oxidase and esterases; both are well known for tannic acid degradation. Upon tannic acid exposure, increased activity of polyphenol oxidase and expression of few new isoforms of esterase were identified by activity staining. 相似文献
106.
107.
Three ribonucleosides responsible for cytokinin activity in Euglena gracilis var Bacillaris tRNA have been isolated and identified as 6-(3-methyl-2-butenylamino)-9-beta-D-ribofuranosylpurine, 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-beta-D-ribofuranosylpurine, and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-beta-D-ribofuranosylpurine. The structures of these compounds were assigned on the basis of their chromatographic properties and ultraviolet and mass spectra which were identical with those of the corresponding synthetic compounds. The elution profiles of cytokinin bioassay activity and of 35S radioactivity suggest the presence of a trace amount of 6-(3-methyl-2-butenylamino)-2-methylthio-9-beta-D-ribofuranosylpurine. 相似文献
108.
109.