Abstract: Two peptide models such as peptide A and peptide B containing serine (S), threonine (T) and tyrosine (Y) were built. The phosphorylation of both peptides was carried out under dry heating conditions. The phosphorylation sites were determined using FT-ICR MS and LTQ-ETD MS/MS. FT-ICR analysis revealed one phosphorlyated site in either peptide under dry heating conditions. In addition, LTQ-ETD MS/MS analysis revealed obvious characteristic peaks of phosphorylated S and Y in peptide A. It was difficult to determine the phosporlyation of T due to the overlapped characteristic peaks of phosphorylated Y and T. However, the LTQ-ETD MS/MS spectrum of peptide B only revealed the phosphorylation of S without the phosphorylation of T. In summary, S and Y were easier to be phosphorylated than T in the same peptide under dry heating conditions.

Key words: phosphorylation, peptide, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), electron transfer dissociation mass spectrometry-mass spectrometry (ETD MS-MS)