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 |
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Authors: | Li Shihong Schöneich Christian Borchardt Ronald T |
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Institution: | (1) Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas, 66045;(2) Department of Pharmaceutical Chemistry, 3006 Malott Hall, School of Pharmacy, The University of Kansas, Lawrence, Kansas, 66045 |
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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. |
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Keywords: | methionine methionine sulfoxide free radicals ascorbate dithiothreitol catalase superoxide dismutase |
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