Enhanced MALDI-TOF MS Analysis of Phosphopeptides Using an Optimized DHAP/DAHC Matrix

Figure 6

The MALDI MS/MS spectra of phosphopeptides (a) T𝛽1, (b) T𝛼3, and (c) T𝛽2 (250 fmol for each on target) from 𝛼-casein and 𝛽-casein were obtained by MALDI-TOF/TOF MS. The sequential losses of H₃PO₄ from the parent ions are noted. The fragment patterns of the peptides are indicated in the magnified MS/MS spectra. “X” in the amino sequence shows a dehydroalanine residue converted from a phosphoserine residue by beta-elimination of H₃PO₄.

(a)

(b)

(c)