Fig. 1

Representative spectral identification to unambiguously localize phosphosites. Phosphopeptides were enriched from WEHI protein digests and analyzed by LC-MS/MS. MS2 spectra are shown for phosphosite identifications of S270 (a) and S279 (b). Not all identified fragments are depicted. An additional oxidation modification of methionine at position 265 was also observed which may be an artifact of events occurring during peptide preparation. The b-ion series, in which the charge is localized to the N-terminal, is shown in red, and the y-ion series, where the charge is localized to the C-terminal, is shown in blue. Vertical lines in the inset represent cleavage sites after fragmentation within the mass spectrometer