Abstract
Site-specific and random fragmentation of human Cu, Zn-superoxide dismutase (Cu, Zn-SOD) was observed following the glycation reaction (the early stage of the Maillard reaction). The fragmentation occurred at a peptide bond between Pro 62 and His 63, as judged by amino acid analysis and sequencing of fragment peptides, yielding a large (15 kD) and a small (5 kD) fragment. In the second step, random fragmentation occurred. The ESR spectrum of the glycated Cu, Zn-SOD suggested that reactive oxygen species (ROS) were implicated in both the steps of fragmentatioa Incubation with glucose resulted in a time-dependent release of Cu2+ from the Cu, Zn-SOD molecule. The released Cu2+ then likely participated in a Fenton's type of reaction to produce hydroxyl radical, which may cause the non-specific fragmentatioa. This is the first report that a site-specific fragmentation of a protein is caused by reactive oxygen species formed by the Maillard reaction.
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