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Figure 4.28.
Oxidation of Arg by
•
OH radical (adapted from xu and chance [261] with
the permission of the American chemical Society).
O
O
N
O
O
O
N
N
N
O
N
N
HO
•
/O
2
+
O
+
+
+
O
O
O
HN
NH
N NH
H
NH
OH
O
NH
2
H
O
O
+16 Da
-22 Da
-23 Da
+5 Da
-10 Da
Figure 4.29.
Oxidation of His by
•
OH radical (adapted from xu and chance [261] with
the permission of the American chemical Society).
the reactions,
•
OH initially attacks the imidazole ring of His at positions c-2,
c-4, or c-5 and generates allyl-type radicals by OH addition. These radicals
were confirmed by continuous-flow EPR experiments [346]. Significantly, allyl
radicals can easily incorporate O
2
and yielded peroxy radicals. Further reaction
of the peroxy radicals gave a mixture of products such as asparagines, aspartic
acid, and 2-oxohistidine [343, 347-350]. Reaction conditions and the sequence
of the local amino acid determine products of oxidation of His by
•
OH.
Aromatic Side Chains.
Oxidation of Trp by
•
OH is complicated and oxidized
products contain mass shifts of +16, +32, +4, and +20 Da, as determined in
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