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  • 1
    Electronic Resource
    Electronic Resource
    Methylglyoxal production in bacteria: suicide or survival? (1998)
    Springer
    Archives of microbiology 170 (1998), S. 209-218 
    Details
    ISSN: 1432-072X
    Keywords: Key words Methylglyoxal ; Cytoplasmic pH ; Potassium ; Glyoxalase ; Glycolysis ; Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methylglyoxal is a toxic electrophile. In Escherichia coli cells, the principal route of methylglyoxal production is from dihydroxyacetone phosphate by the action of methylglyoxal synthase. The toxicity of methylglyoxal is believed to be due to its ability to interact with the nucleophilic centres of macromolecules such as DNA. Bacteria possess an array of detoxification pathways for methylglyoxal. In E. coli, glutathione-based detoxification is central to survival of exposure to methylglyoxal. The glutathione-dependent glyoxalase I-II pathway is the primary route of methylglyoxal detoxification, and the glutathione conjugates formed can activate the KefB and KefC potassium channels. The activation of these channels leads to a lowering of the intracellular pH of the bacterial cell, which protects against the toxic effects of electrophiles. In addition to the KefB and KefC systems, E. coli cells are equipped with a number of independent protective mechanisms whose purpose appears to be directed at ensuring the integrity of the DNA. A model of how these protective mechanisms function will be presented. The production of methylglyoxal by cells is a paradox that can be resolved by assigning an important role in adaptation to conditions of nutrient imbalance. Analysis of a methylglyoxal synthase-deficient mutant provides evidence that methylglyoxal production is required to allow growth under certain environmental conditions. The production of methylglyoxal may represent a high-risk strategy that facilitates adaptation, but which on failure leads to cell death. New strategies for antibacterial therapy may be based on undermining the detoxification and defence mechanisms coupled with deregulation of methylglyoxal synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050635
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  • 2
    Electronic Resource
    Electronic Resource
    From famine to feast: the role of methylglyoxal production in Escherichia coli (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The enzyme methylglyoxal synthase (MGS) was partially purified from Escherichia coli extracts, and the amino-terminal sequence of candidate proteins was determined, based on the native protein being a tetramer of about 69 kDa. Database analysis identified an open reading frame in the E. coli genome, YccG, corresponding to a protein of 16.9 kDa. When amplified and expressed from a controlled promoter, it yielded extracts that contained high levels of MGS activity. MGS expressed from the trc promoter accumulated to approximately 20% of total cell protein, representing approximately 900-fold enhanced expression. This caused no detriment during growth on glucose, and the level of methylglyoxal (MG) in the medium rose to only 0.08 mM. High-level expression of MGS severely compromised growth on xylose, arabinose and glycerol. A mutant lacking MGS was constructed, and it grew normally on a range of carbon sources and on low-phosphate medium. However, the mutant failed to produce MG during growth on xylose in the presence of cAMP, and growth was inhibited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00700.x
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  • 3
    Electronic Resource
    Electronic Resource
    The role of glyoxalase I in the detoxification of methylglyoxal and in the activation of the KefB K+ efflux system in Escherichia coli (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The glyoxalase I gene (gloA) of Escherichia coli has been cloned and used to create a null mutant. Cells overexpressing glyoxalase I exhibit enhanced tolerance of methylglyoxal (MG) and exhibit elevated rates of detoxification, although the increase is not stoichiometric with the change in enzyme activity. Potassium efflux via KefB is also enhanced in the overexpressing strain. Analysis of the physiology of the mutant has revealed that growth and viability are quite normal, unless the cell is challenged with MG either added exogenously or synthesized by the cells. The mutant strain has a low rate of detoxification of MG, and cells rapidly lose viability when exposed to this electrophile. Activation of KefB and KefC is diminished in the absence of functional glyoxalase I. These data suggest that the glutathione-dependent glyoxalase I is the dominant detoxification pathway for MG in E. coli and that the product of glyoxalase I activity, S-lactoylglutathione, is the activator of KefB and KefC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00701.x
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  • 4
    Electronic Resource
    Electronic Resource
    Activation potassium efflux from Escherichia coli by glutathione metabolites (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The mechanism by which N-ethylmaleimide (NEM) elicits potassium efflux from Escherichia coli has been investigated. The critical factor is the formation of specific glutathione metabolites that activate transport systems encoded by the kefB and kefC gene products. Formation of N-ethyl-succinimido-S-glutathione (ESG) leads to the activation of potassium efflux via these transport systems. The addition of dithiothreitol and other reducing agents to cells reverses this process by causing the breakdown of ESG and thus removing the activator of the systems. Chlorodinitrobenzene, p-chloromercuribenzoate and phenylmaleimide provoke similar effects to NEM. Iodoacetate, which leads to the formation of S-carboxymethyl-glutathione, does not activate the systems but does prevent the action of NEM. It is concluded that the KefB and KefC systems are gated by glutathione metabolites and that the degree to which they are activated is dependent upon the nature of the substituent on the sulphydryl group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb00607.x
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  • 5
    Electronic Resource
    Electronic Resource
    The cloning and DNA sequence of the gene for the glutathione-regulated potassium-efflux system KefC of Escherichia coli (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The kefC gene of Escherichia coli encodes a potassium-efflux system that is regulated by glutathione metabolites. The close proximity of the E. coli kefC gene to the folA gene, encoding dihydrofolate reductase, has been utilized to clone the structural gene for the system from a Clarke-Carbon plasmid. The cloned gene has been refined to a region of DNA approximately 2.1 kb in length using exonuclease III-generated deletions and random Muc/M1734 (IacZ) insertions. The direction of transcription has been deduced from the orientation of the Mu insertions in the cloned DNA. A hybrid protein consisting of approximately two thirds of the KefC protein fused to β-galactosidase has been shown to be membrane-located. The DNA sequence of the gene has been determined and an open reading frame of 1.86kb has been located which could encode a protein of 620 amino acids (7901 0Da). Using the T7 expression system a membrane protein, of apparent molecular mass 55–60 kDa, has been shown to be encoded by the kefC gene. The predicted protein sequence shows a highly hydrophobic amino-terminus and a strongly hydrophilic carboxy-terminus, Comparison of the amino acid sequence of the kefC gene product with those of two glutathione-utilizing enzymes, glyoxalase and dehalogenase, has revealed some similarities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb00731.x
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  • 6
    Electronic Resource
    Electronic Resource
    A novel, non-invasive promoter probe vector: cloning of the osmoregulated proU promoter of Escherichia coli K12 (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have constructed a novel promoter probe plasmid pSB40, containing a unique lac-α-tetracycline marker gene tandem, which allows for both positive and negative selection of active promoters. Promoters cloned in pSB40 can be readily mobilized as EcoR1 cassettes. Using this vector we have performed a non-invasive analysis of the E. coli chromosome for promoters regulated by osmotic upshift. Only one such promoter, subsequently identified as part of the proU operon, was isolated. A sequence of 253bp, sufficient to mediate osmotic regulation of the proU promoter, was defined. This E coli promoter was normally regulated in Salmonella typhimurium, Klebsiella and Citrobacter but not in Shigella. A proU-luxAB fusion plasmid was constructed and used to monitor in vivo real-time kinetics of proU induction following osmotic upshock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00252.x
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular characterization of the proU loci of Salmonella typhimurium and Escherichia coli encoding osmoregulated glycine betaine transport systems (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The proU loci of Salmonella typhimurium and Escherichia coli encode high-affinity glycine betaine transport systems which play an important role in survival under osmotic stress. Transcription of the proU locus is tightly regulated by osmolarity and this regulation appears to be mediated by osmotically induced changes in DNA supercoiling. In order to study the regulatory mechanisms involved we have cloned and characterized the proU locus of S. typhimurium by an in vivo transductional procedure. The locus is shown to consist of at least three genes, designated proVWX, cotranscribed as a single operon. The first gene in the operon encodes a protein sharing considerable sequence identity with ATP-binding proteins from other periplasmic transport systems. Unexpectedly, the highly expressed periplasmic glycine betaine binding protein was found to be encoded by a distal gene, proX, in the operon. The operon has no significant internal promoters but is expressed from a single osmoregulated promoter whose transcription start site has been mapped. The proU promoter of E. coli has also been sequenced and the transcription start site shown to be similar to that of S. typhimurium. Evidence is presented which suggests that, besides de novo glycine betaine uptake, an important function of ProU may be the recapture and recycling of other osmolytes that leak from the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00253.x
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  • 8
    Electronic Resource
    Electronic Resource
    Carbohydrate transport inClostridium pasteurianum (1982)
    Springer
    Bioscience reports 2 (1982), S. 47-53 
    Details
    ISSN: 1573-4935
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01142198
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  • 9
    Electronic Resource
    Electronic Resource
    The rpoA341 allele of Escherichia coli specifically impairs the transcription of a group of positively-regulated operons (1988)
    Springer
    Molecular genetics and genomics 214 (1988), S. 148-152 
    Details
    ISSN: 1617-4623
    Keywords: RNA polymerase ; Transcription ; Positive regulation ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The specificity of the transcription defect caused by the rpoA341 (phs) allele has been investigated. Three apparently unlinked genetic systems have been found to be impaired in their transcription by this mutant allele of the alpha subunit of RNA polymerase. These three systems, the melAB operon the cysA locus and the ara regulon, are apparently unrelated other than by their requirement for a regulon-specific positive regulator for the initiation of transcription. Expression of the gene for the positive regulator does not appear to be significantly affected in any of the three systems. However, mutations that render expression of the araBAD operon independent of the regulatory protein also confer insensitivity to the rpoA341 allele. The siginificance of these observations is discussed in the context of models of positive regulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00340193
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  • 10
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    Conformational state of the MscS mechanosensitive channel in solution revealed by pulsed electron-electron double resonance (PELDOR) spectroscopy (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-09-10
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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