Fig. 1
From: Evaluation of top-down mass spectral identification with homologous protein sequences
Comparison of the theoretical spectrum (top) of an unmodified protein sequence EPPLSQETFS and the theoretical spectrum (bottom) of a modified proteoform EPPLS[phosphorylation]QETFS, in which the serine residue is phosphorylated. Only N-terminal fragment peaks are included in the theoretical spectra to simply the comparison. The fragment peaks in the box are shifted to the right by 79.97 Da in the bottom spectrum because of the phosphorylation