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    Sulfoxidation of methionine in small model peptides: Evaluation of the ferric chloride/mercaptoethanol oxidizing system

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    Issue Date
    1995-05-31
    Author
    Murthy, A. Savitri
    Publisher
    University of Kansas
    Type
    Thesis
    Degree Level
    M.S.
    Discipline
    Chemistry
    Rights
    This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.
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    Abstract
    Conversion of methionine to methionine sulfoxide can take place during postranslational modification, formulation, storage or synthesis of proteins. Therefore, methionine sulfoxidation is a major concern to pharmaceutical industries. Small model peptides containing methionine were oxidized by mercaptoethanol/FeCl, system in phosphate buffer. These studies were carried out to investigate the factors affecting methionine oxidation and the mechanism involved in the sulfoxidation. The effect of pH, buffer concentration, Fe(III) concentration, type of thiol, mercaptoethanol concentration and EDTA concentration on the formation of methionine sulfoxide was examined. The model peptides studied included His-Met, Met-His, Gly-Met, Gly- Met-Gly, Gly-Gly-Met and Met-Gly-Gly. The initial rate of formation of methionine sulfoxide was observed to be dependant on the iron concentration and thiol concentration. However, the initial rate of formation of methionine sulfoxide was independent of the phosphate buffer concentration. The presence of EDTA not only suppressed the formation of sulfoxide but also caused an increase in peptide degradation. The influence of the location of methionine on the yield of sulfoxide was also investigated. Maximum sulfoxide formation was observed when methionine was in the carboxyl-terminal position in the peptide, His-Met. The possible role of various reactive oxygen species was studied by using various trapping agents. The involvement of freely diffusible hydrogen peroxide, superoxide, and OH. in this oxidation process was found to be negligible. It may be also possible that these reactive oxygen species may not be involved in the rate determining step. However, the presence of bound reactive oxygen species cannot be ruled out, as these may not be trapped by the trapping agents used in this study. These studies and future elucidation of the chemical mechanisms involved in methionine sulfoxidation will provide a better understanding of the susceptibility of various proteins and peptides to degradation.
    Description
    Thesis (M.S.)--University of Kansas, Chemistry, 1995.
    URI
    http://hdl.handle.net/1808/33651
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    • Theses [3828]

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    Lawrence, KS 66045
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    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

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