Mass Spectrometry of Putrescine, Spermidine, and Spermine Covalently Attached to Francisella tularensis Universal Stress Protein and Bovine Albumin

Figure 6

MS/MS spectrum for peptide NE(127.12)LTEFAK of bovine serum albumin covalently modified by spermidine on Glu 69 (E69) by the action of EDC. The parent ion mass in charge state +2 is 540.11 m/z. A y-ion sequence y1–y6 is present. This portion of the sequence does not include the labeled glutamate. A b-ion sequence, b3–b7, also is present. All of the masses in this sequence are consistent with the presence of spermidine added mass (127.12 Da). The y-ion and b-ion sequences account for all residues in the peptide. A nonsequence mass at 1007.55 Da is consistent with a neutral loss of 71 Da from spermidine on the parent ion. Most unlabeled fragments correspond to internal fragments or to loss of amine, water, or CO from assigned fragments.