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  • 1
    Electronic Resource
    Electronic Resource
    Chemical Pathways of Peptide Degradation. V. Ascorbic Acid Promotes Rather than Inhibits the Oxidation of Methionine to Methionine Sulfoxide in Small Model Peptides (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 1572-1579 
    Details
    ISSN: 1573-904X
    Keywords: methionine ; methionine sulfoxide ; free radical ; ascorbate ; EDTA ; histidine ; catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of primary structure and external conditions on the oxidation of methionine to methionine sulfoxide by the ascorbate/Fe3+ system was studied in small model peptides. Degradation kinetics and yield of sulfoxide formation were dependent on the concentration of ascorbate and H+, with a maximum rate observed at pH 6–7. Phosphate buffer significantly accelerated the peptide degradation compared to Tris, HEPES, and MOPS buffers; however, the formation of sulfoxide was low. The oxidation could not be inhibited by the addition of EDTA. Other side products besides sulfoxide were observed, indicating the existence of various other pathways. The influence of methionine location at the C terminus, at the N terminus, and in the middle of the sequence was investigated. The presence of histidine in the sequence markedly increased the degradation rate as well as the sulfoxide production. The histidine catalysis of methionine oxidation occurred intramolecularly with a maximum enhancement of the oxidation rate and sulfoxide production when one residue was placed between the histidine and the methionine residue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018960300769
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  • 2
    Electronic Resource
    Electronic Resource
    Chemical Pathways of Peptide Degradation. VIII. Oxidation of Methionine in Small Model Peptides by Prooxidant/Transition Metal Ion Systems: Influence of Selective Scavengers for Reactive Oxygen Intermediates (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 348-355 
    Details
    ISSN: 1573-904X
    Keywords: methionine ; methionine sulfoxide ; free radicals ; ascorbate ; dithiothreitol ; catalase ; superoxide dismutase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the presence of oxygen, Fe(III), and an appropriate electron donor (e.g. ascorbic acid, dithiothreitol), the oxidation of methionine residues to methionine sulfoxides in small model peptides can be induced. It is shown in this study that these oxidations can be retarded by catalase in a pH-dependent manner, by some hydroxyl radical scavengers, and by azide. In contrast, superoxide dismutase has only a minimal effect, indicating that the superoxide radical does not contribute significantly to the oxidation of the methionine residue. The experimental results can be interpreted by invoking hydrogen peroxide as the major oxidizing species at pH ≤ 7, whereas the involvement of free hydroxyl radicals seems to be negligible. Other reactive oxygen intermediates such as iron-bound hydroperoxy, or site-specifically generated reactive oxygen species may be actively involved in the oxidation of methionine residues at pH 〉 7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016240115675
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    Paper (German National Licenses)
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