Supplemental Data
MH+32
MH+32-H2O2
MH+32-H2O
MH+32
MH+32-H2O
Figure S1. MS/MS of the oxidation product M + 32 of GVG (a) after oxidation and
HPLC (b) after oxidation, HPLC, and incubated with methionine amide for 24 h.
MS/MS data of the aromatic peptide GFG
Reactions of aromatic residues with hydroxyl radicals primarily involve addition of
the hydroxyl radical to the aromatic side chain, with formation of an aromatic alcohol
combined with an aromatic radical [6]. The MS/MS analyses of the aromatic peptide
GFG show a loss of water from the M + 32 product both before and after incubation with
methionine amide, but no loss of a peroxide-based neutral (data not shown). When the
unoxidized peptide and oxidized peptide are compared after incubation with methionine
amide, the oxidized sample has a more intense peak for the oxidized product of
methionine amide than does the unoxidized sample (Figure S2); also the M + 32 product
of the oxidized peptide GFG decreases after an incubation period with methionine amide
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(Table 1). These data indicate some component of the mixture of M+32 ions is oxidizing
the methionine amide, although there is no observed loss of hydrogen peroxide in the
MS/MS data to support assignment as a peptidyl hydroperoxide. Based on these data, we
are unable to determine the structure of the methionine-reactive M+32 oxidation product
of phenylalanine, but we can conclude that aromatic residue oxidation does result in a
minor amount of protein-bound secondary oxidant capable of directly oxidizing
methionine residues.
Met-NH2
MH
Met-NH2+16
Met-NH2
Met-NH2+16
Figure S2. (a) Unoxidized GFG incubated with 1.45mM methionine amide for 24 h. (b)
Oxidized GFG incubated with 1.45mM methionine amide for 24 h.
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