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排序方式: 共有208条查询结果,搜索用时 343 毫秒
61.
Vladimir S. Bondar Marelle G. Boersma Eugene L. Golovlev Jacques Vervoort Willem J.H. Van Berkel Zoya I. Finkelstein Inna P. Solyanikova Ludmila A. Golovleva Ivonne M.C.M. Rietjens 《Biodegradation》1998,9(6):475-486
Of all NMR observable isotopes 19F is the one perhaps most convenient for studies on biodegradation of environmental pollutants. The reasons underlying this potential of 19F NMR are discussed and illustrated on the basis of a study on the biodegradation of fluorophenols by four Rhodococcus strains. The results indicate marked differences between the biodegradation pathways of fluorophenols among the various Rhodococcus species. This holds not only for the level and nature of the fluorinated biodegradation pathway intermediates that accumulate, but also for the regioselectivity of the initial hydroxylation step. Several of the Rhodococcus species contain a phenol hydroxylase that catalyses the oxidative defluorination of ortho-fluorinated di- and trifluorophenols. Furthermore, it is illustrated how the 19F NMR technique can be used as a tool in the process of identification of an accumulated unknown metabolite, in this case most likely 5-fluoromaleylacetate. Altogether, the 19F NMR technique proved valid to obtain detailed information on the microbial biodegradation pathways of fluorinated organics, but also to provide information on the specificity of enzymes generally considered unstable and, for this reason, not much studied so far. 相似文献
62.
C P van Mierlo P Lijnzaad J Vervoort F Müller H J Berendsen J de Vlieg 《European journal of biochemistry》1990,194(1):185-198
The tertiary structure of the non-crystallizable two-electron-reduced Megasphaera elsdenii flavodoxin (15 kDa, 137 amino acid residues) has been determined using nuclear Overhauser enhancement restraints extracted from two-dimensional 1H-NMR spectra. A tertiary structure satisfying the experimental restraints very well (maximum NOE violation of 66 pm) was obtained with use of restrained molecular dynamics, using 509 distance restraints (including one non-NOE) on a starting structure modeled from the crystal structure of one-electron-reduced Clostridium MP flavodoxin. The protein consists of a central parallel beta-sheet surrounded on both sides by two alpha-helices. The flavin is positioned at the periphery of the molecule. The tertiary structure of the protein is highly defined with the exception of the flavin. The latter is expected to result from performing the restrained molecular dynamics simulation without water molecules and without proper charges on the flavin. The flavin, including the phosphate, the ribityl side chain and the isoalloxazine ring, is solvent accessible under the experimental conditions used and evidenced by a two-dimensional amide exchange experiment. This accessibility is expected to be important in the redox potential regulation of the semiquinone/hydroquinone couple of the protein. The amide exchange against deuterons and several typical line shapes in the two-dimensional NMR spectra are consistent with the structure generated. The structure is discussed in detail. 相似文献
63.
Reaction pathways for biodehalogenation of fluorinated anilines 总被引:1,自引:0,他引:1
Pathways for biodehalogenation of fluorinated aniline derivatives were investigated. Microsomal NADPH-dependent dehalogenation of fluoroanilines was shown to proceed by three different reaction pathways. The first route appeared to result in monooxygenation at a fluorinated position and release of the fluorine atom as a fluoride anion. The primary additional reaction product formed is the reactive quinoneimine, not the 4-hydroxyaniline. In NADPH-containing microsomal systems with 4-fluoro-substituted anilines, formation of the 4-hydroxyaniline derivative is observed because NADPH chemically reduces this quinoneimine metabolite. A second pathway for dehalogenation proceeds by protein binding of a fluoro-containing (semi)quinoneimine metabolite, the formation of which may result from the mono-oxygenase reaction (pathway 1) and/or from (re)oxidation of a hydroxyaniline metabolite by superoxide anion radicals produced by the microsomal system. This latter reaction pathway becomes more important with increasing number of fluoro-substituents in the fluoroaniline derivative. The higher ratio of fluoride anion formed to 4-hydroxyaniline derivative detected in incubations with liver microsomes from dexamethasone-treated rats, as compared to incubations with liver microsomes from control rats, can in part be explained by the higher production of superoxide anion radicals observed in the dexamethasone systems. The third mechanism was shown to proceed by formation of a hydroxylated metabolite that loses fluoride anion upon exposure to oxygen. The reactive intermediate formed upon oxygen exposure might be the semiquinoneimine which loses its fluorine atom as a fluoride anion upon dimerization or polymerization and/or protein binding. The fluorohydroxyanilines, in which the hydroxyl group is ortho or para with respect to the fluoro substituent, appear especially to be highly unstable and lose fluoride anion in the presence of oxygen. Finally, it is concluded that all three pathways for dehalogenation of fluorinated aniline derivatives are bioactivation pathways. The reactivity of the (semi)quinoneimines formed in these reactions is dependent on their substitution pattern and increases with increasing number of fluoro-substituents. Therefore, bioactivation for a series of fluorinated aniline derivatives, can be expected to vary with the substitution pattern and to increase with increasing number of halogen substituents. 相似文献
64.
Finkel'shteĭn ZI Baskunov BP Golovlev EL Moiseeva OV Vervoort J Rietjens I Golovleva LA 《Mikrobiologiia》2000,69(1):49-57
Study of the conversion of chlorophenols by Rhodococcus opacus 1G, R. rhodnii 135, R. rhodochrous 89, and R. opacus 1cp disclosed the dependence of the conversion rate and pathway on the number and position of chlorine atoms in the aromatic ring. The most active chlorophenol converter, strain R. opacus 1cp, grew on each of the three isomeric monochlorophenols and on 2,4-dichlorophenol; the rate of growth decreased from 4-chlorophenol to 3-chlorophenol and then to 2-chlorophenol. The parameters of growth on 2,4-dichlorophenol were the same as on 3-chlorophenol. None of the strains studied utilized trichlorophenols. A detailed study of the pathway of chlorophenol transformation showed that 3-chloro-, 4-chloro-, and 2,4-dichlorophenol were utilized by the strains via a modified ortho-pathway. 2-Chlorophenol and 2,3-dichlorophenol were transformed by strains R. opacus 1cp and R. rhodochrous 89 via corresponding 3-chloro- and 3,4-dichloropyrocatechols, which were then hydroxylated with the formation of 4-chloropyrogallol and 4,5-dichloropyrogallol; this route had not previously been described in bacteria. Phenol hydroxylase of R. opacus 1G exhibited a previously undescribed catalytic pattern, catalyzing oxidative dehalogenation of 2,3,5-trichlorophenol with the formation of 3,5-dichloropyrocatechol but not hydroxylation of the nonsubstituted position 6. 相似文献
65.
Vervoort EB Bultema JB Schuurman-Wolters GK Geertsma ER Broos J Poolman B 《Journal of molecular biology》2005,346(3):733-743
The mannitol permease (EII(Mtl)) from Escherichia coli couples mannitol transport to phosphorylation of the substrate. Renewed topology prediction of the membrane-embedded C domain suggested that EII(Mtl) contains more membrane-embedded segments than the six proposed previously on the basis of a PhoA fusion study. Cysteine accessibility was used to confirm this notion. Since cysteine 384 in the cytoplasmic B domain is crucial for the phosphorylation activity of EII(Mtl), all cysteine mutants contained this activity-linked cysteine residue in addition to those introduced for probing the membrane topology of the protein. To distinguish between the activity-linked cysteine and the probed cysteine, either trypsin was used to specifically digest the two cytoplasmic domains (A and B), thereby removing Cys384, or Cys384 was protected by phosphorylation from alkylation by N-ethylmaleimide (NEM). Our data show that upon phosphorylation EII(Mtl) undergoes major conformational changes, whereby residues in the putative first cytoplasmic loop become accessible to NEM. Other residues in this loop were accessible to NEM in intact cells and inside-out membrane vesicles, but cysteine residues at these positions only reacted with the membrane-impermeable sulfhydryl reagent from the periplasmic side of the protein. These and other results suggest that the predicted loop between TM2 and TM3 may fold back into the membrane and form part of the translocation path. 相似文献
66.
Meij P Bloemena E Palmen N Brink A Vervoort MB Meijer CJ Middeldorp JM 《Cellular immunology》2001,208(1):25-33
Epstein-Barr virus (EBV) gene expression in tumor cells of posttransplant lymphoproliferative disorder (PTLD) patients resembles that of EBV transformed B-cell lines (LCL). EBV-specific cytotoxic T-lymphocytes can be generated by stimulating peripheral blood lymphocytes with autologous LCL. We describe a standardized method for the growth inactivation and cryopreservation of LCL for optimal T-cell stimulation and analyzed the function and phenotype of responding T-cells. LCL growth was completely blocked by mitomycin C treatment (McLCL) and McLCL could be cryopreserved while retaining excellent APC function. McLCL stimulated both CD4(+) and CD8(+) T-cells as measured by HLA-DR and CD25 expression using FACS analysis. EBV-specific CTL activity and T-cell proliferation were induced and immunocytochemical staining showed CD4(+) and (granzyme B positive) CD8(+) T-cells rosetting with McLCL. Granzymes A and B, IFN-gamma, and IL-6 were detected at significant levels in the supernatant. Thus, ex vivo T-cell activation with cryopreserved McLCL results in activation of both CD4(+) and CD8(+) T-cells producing a Th1-like cytokine profile, making this a suitable protocol for adoptive therapy of PTLD. 相似文献
67.
Z. I. Finkel’shtein B. P. Baskunov E. L. Golovlev O. V. Moiseeva J. Vervoort I. Rietjens L. A. Golovleva 《Microbiology》2000,69(1):40-47
Study of the conversion of chlorophenols byRhodococcus opacus 1G,R. rhodnii 135,R. rhodochrous 89, andR. opacus 1cp disclosed the dependence of the conversion rate and pathway on the number and position of chlorine atoms in the aromatic
ring. The most active chlorophenol converter, strainR. opacus 1cp, grew on each of the three isomeric monochlorophenols and on 2,4-dichlorophenol; the rate of growth decreased from 4-chlorophenol
to 3-chlorophenol and then to 2-chlorophenol. The parameters of growth on 2,4-dichlorophenol were the same as on 3-chlorophenol.
None of the strains studied utilized trichlorophenols. A detailed study of the pathway of chlorophenol transformation showed
that 3-chloro-, 4-chloro-, and 2,4-dichlorophenol were utilized by the strains via a modifiedortho-pathway. 2-Chlorophenol and 2,3-dichlorophenol were transformed by strainsR. opacus 1cp andR. rhodochrous 89 via corresponding 3-chloro- and 3,4-dichlorocatechols, which were then hydroxylated with the formation of 4-chloropyrogallol
and 4,5-dichloropyrogallol; this route had not previously been described in bacteria. Phenol hydroxylase ofR. opacus 1G exhibited a previously undescribed catalytic pattern, catalyzing oxidative dehalogenation of 2,3,5-trichlorophenol with
the formation of 3,5-dichlorocatechol but not hydroxylation of the nonsubstituted position 6. 相似文献
68.
69.
Kasper A. Hettinga Fabiola M. Reina Sjef Boeren Lina Zhang Gerard H. Koppelman Dirkje S. Postma Jacques J. M. Vervoort Alet H. Wijga 《PloS one》2015,10(3)
Background
Breastfeeding has been linked to a reduction in the prevalence of allergy and asthma. However, studies on this relationship vary in outcome, which may partly be related to differences in breast milk composition. In particular breast milk composition may differ between allergic and non-allergic mothers. Important components that may be involved are breast milk proteins, as these are known to regulate immune development in the newborn. The objective of this study was therefore to explore differences in the proteins of breast milk from 20 allergic and non-allergic mothers. The results from this comparison may then be used to generate hypotheses on proteins associated with allergy in their offspring.Methods
Milk samples from allergic and non-allergic mothers were obtained from the PIAMA project, a prospective birth cohort study on incidence, risk factors, and prevention of asthma and inhalant allergy. Non-targeted proteomics technology, based on liquid chromatography and mass spectrometry, was used to compare breast milk from allergic and non-allergic mothers.Results
Nineteen proteins, out of a total of 364 proteins identified in both groups, differed significantly in concentration between the breast milk of allergic and non-allergic mothers. Protease inhibitors and apolipoproteins were present in much higher concentrations in breast milk of allergic than non-allergic mothers. These proteins have been suggested to be linked to allergy and asthma.Conclusions
The non-targeted milk proteomic analysis employed has provided new targets for future studies on the relation between breast milk composition and allergy. 相似文献70.
Elke Heremans Evelien Nackaerts Griet Vervoort Sarah Vercruysse Sanne Broeder Carolien Strouwen Stephan P. Swinnen Alice Nieuwboer 《PloS one》2015,10(11)