Figure 15.4.
Tandem mass spectrum showing the simultaneous presence of nitrohydroxytryptophan and methionine sulfoxide in the peptide ([M+2H]2+ ion at m/z 721.0) following peroxynitrite treatment. The fragmentation profile of the peptide is also modified considerably, with y6, y7, and y8 becoming particularly abundant. In contrast, y5 relative intensity is low, suggesting that nitrohydroxytryptophan might repress fragmentation on its C-terminal bond. M#, methionine sulfoxide; W*, nitrohydroxytryptophan.