Figure 6. CDK1/cyclin B mediates phopshorylation of Ubc9 at Serine 71.
IMAC enriched tryptic peptides of Ubc9 were detected by CID tandem mass spectra. Precursor ion m/z 802.8 (charge state +2) representing the phosphopeptide MLFKDDYPSpSPPK. Residues bearing phosphate moieties are indicated with p. “b” and “y” ions series represent fragment ions containing the N- and C-termini of the peptide, respectively. Product ions marked with * resulted from elimination of NH3. The mass of 98 on the peaks was derived from neutral losses (-97.9769 Da) of phosphoric acid (H3PO4).