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

Figure 7

MS/MS spectrum for peptide IVDFQ(71.07)HSIEQEAK of rUsp/His₆ covalently modified by putrescine on Gln 55 by the action of microbial transglutaminase. The parent ion in charge state +3 is 539.95 m/z. (a) A y-ion sequence, y1–y8, and a b-ion sequence, b2–b7. Only the b7 ion includes the putrescine adduct. The y4 and b4 masses are identical. (b) An internal fragment sequence from if3 to if10. Masses for all of the fragments in this series are consistent with the presence of the putrescine added mass (71.07 Da). In addition, fragments from a doubly charged sequence, y10⁺² to y12⁺², are consistent with the presence of the added mass for putrescine. The sequences in panels (a and b) account for all residues in the peptide. A nonsequence fragment at 155.12 Da is consistent with a signature ion for the glutamine-putrescine construct. Most unassigned fragments correspond to internal fragments or to loss of amine, water, or CO from assigned fragments.

(a)

(b)