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. 2012 Jun 4;7(6):e37984. doi: 10.1371/journal.pone.0037984

Figure 4. ESI tandem mass spectrometry confirms the presence and location of the phosphorylated tyrosine.

Figure 4

The ESI-MS/MS fragmentation spectrum of Etp peptide GKTMLFGQWLEQKEIPAP(pY)RK (residues 113–123, pY is the phosphorylated tyrosine). The parent peptide was a +4 H ion with mass 2599.29 amu (−0.0134 amu from predicted size). The schematic at the top of the figure shows the identified y fragments referred to in the spectra. All of the y fragments include the peptide's C-terminus and have masses consistent with the phosphorylated Y121 (pY) residue. For example, the m/z for fragments y3 and y2 are 546.2 and 303.2, respectively. The difference 243 is the exact mass of a phosphotyrosyl residue. The labeled b fragments originate at the N-terminus of the peptide but do not include the pY residue.