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. Author manuscript; available in PMC: 2017 Aug 14.
Published in final edited form as: Anal Chem. 2017 Apr 17;89(12):6367–6376. doi: 10.1021/acs.analchem.7b00212

Figure 1. ETD and AI-ETD spectra of a phosphopeptide with several potential phosphosites.

Figure 1

ETD produces moderate fragmentation of doubly protonated precursor of peptide SVSTpSPSILPAYLK but fails to confidently localize the modified phosphoserine (Xcorr 1.09, ~46% backbone sequence coverage). Conversely, AI-ETD generates extensive fragmentation with c/z and b/y ion series to localize the phosphosite with high confidence (Xcorr 5.97, 100% backbone sequence coverage). Spectra are on the same intensity scale, and the grey regions are scaled to be ten percent of original intensity.