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  • Analytical Chemistry and Spectroscopy  (2)
  • Escherichia coli  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Colicin M is inactivated during import by its immunity protein (1996)
    Springer
    Molecular genetics and genomics 251 (1996), S. 388-396 
    Details
    ISSN: 1617-4623
    Keywords: Escherichia coli ; Colicin M ; Immunity ; Periplasm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Colicin M (Cma) displays a unique activity that interferes with murein and O-antigen biosynthesis through inhibition of lipid-carrier regeneration. Immunity is conferred by a specific immunity protein (Cmi) that inhibits the action of colicin M in the periplasm. The subcellular location of Cmi was determined by constructing hybrid proteins between Cmi and the TEM-β-lactamase (BlaM), which confers resistance to ampicillin only when it is translocated across the cytoplasmic membrane with the aid of Cmi. The smallest Cmi'-BlaM hybrid that conferred resistance to 50 μg/ml ampicillin contained 19 amino acid residues of Cmi; cells expressing Cmi'-BlaM with only five N-terminal Cmi residues were ampicillin sensitive. These results support a model in which the hydrophobic sequence of Cmi comprising residues 3–23 serves to translocate residues 24–117 of Cmi into the periplasm and anchors Cmi to the cytoplasmic membrane. Residues 8–23 are integrated in the cytoplasmic membrane and are not involved in Cma recognition. This model was further tested by replacing residues 1–23 of Cmi by the hydrophobic amino acid sequence 1–42 of the penicillin binding protein 3 (PBP3). In vivo, PBP3'-'Cmi was as active as Cmi, demonstrating that translocation and anchoring of Cmi is not sequence-specific. Substitution of the 23 N-terminal residues of Cmi by the cleavable signal peptide of BlaM resulted in an active BlaM'-'Cmi hybrid protein. The immunity conferred by BlaM'-'Cmi was high, but not as high as that associated with Cmi and PBP3'-'Cmi, demonstrating that soluble Cmi lacking its membrane anchor is still active, but immobilization in the cytoplasmic membrane, the target site of Cma, increases its efficiency. CmiΔ1-23 remained in the cytoplasm and conferred no immunity. We propose that the immunity protein inactivates colicin M in the periplasm before Cma can reach its target in the cytoplasmic membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02172531
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  • 2
    Electronic Resource
    Electronic Resource
    Application of the time-dependent wavepacket method to mass spectrometric studies of molecular excitation and dissociation (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 358-362 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new time-dependent wavepacket approach has been applied to illustrate a rigorous method of calculating the transition function for bound-to-continuum transitions in translational energy spectrometric experiments. The method is numerically exact and fully quantal, and is devoid of any classical or semi-classical approximations. The validity of the hitherto-applied reflection approximation is investigated in a comparative study. The method has been applied to two different translational energy spectrometry experiments: collision-induced dissociation of CO+ and collisional excitation of H2.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290090418
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of (13C)ethanol incorporation into very-low-density lipoprotein triglycerides using gas chromatography/isotope ratio mass spectrometry coupling (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 20 (1991), S. 777-782 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas chromatography/isotope ratio mass spectrometry (GC/IRMS) coupling was used to evaluate (13C)ethanol incorporation into plasmatic very-low-density lipoprotein (VLDL) triglycerides of three healthy human volunteers. After the perfusion of 13C-enriched alcohol, VLDL triglyceride fractions were extracted from plasma samples and prepared for the analysis of (13C)fatty acid methyl esters. The GC/IRMS coupling line, the analytical procedure and the data collection are described. The results show that ethanol itself may be used as a substrate for lipogenesis, though to a small extent: less than 10% of VLDL triglycerides may be derived from this metabolic pathway. Ethanol incorporates predominantly into myristic and palmitic acid. The small amount of sample material required for analysis, which minimizes the amount of isotope-labelled substrate required, makes this technique a valuable tool for metabolic investigations in human subjects.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200201206
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