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

Figure 13

False positive spermine adduct on bovine serum albumin. Protein prospector assigned the sequence to TKCamCamTE(184.09)SLVNR with glutamate labeled by spermine and with carbamidomethylated cysteine residues (Cam). The parent ion mass in charge state +2 is 776.35 m/z. This assignment proved to be incorrect after manual evaluation. Fragments y2–y5 were assigned to the y-ion sequence SLVNR. The y6 fragment for Glu (184.09) expected to be at 901.48 Da was not found in the data. Rather, a mass at 717.40 Da was present that was consistent with an unlabeled glutamate. This fragment is labeled . The asterisk identifies the missed search engine assignment. Subsequent fragments – are consistent with additional fragments that do not contain spermine. Fragments – are not part of the Protein Prospector assignment.