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

Figure 5

MS/MS spectrum for peptide NLPPLTAD(70.06)FAEDK⁺³ of bovine serum albumin covalently bound to putrescine at Asp 331 through the action of EDC. The parent ion mass in charge state +3 is 500.94 m/z. (a) A y-ion sequence, y1–y10. The interval between fragment y5 and y6 is consistent with aspartate-putrescine. Masses of the y7–y10 fragments are consistent with the presence of putrescine. The mass at 228.14 Da is consistent with the b2 ion, NL. (b) A doubly charged y-ion sequence for y8–y11. This sequence together with the sequences in panel (a) accounts for all of the residues in the peptide. A nonsequence fragment at 141.10 Da is consistent with a signature ion for the aspartate-putrescine construct. Most of the remaining, unassigned fragments correspond to internal fragments or to loss of amine, water, or CO from assigned fragments.

(a)

(b)