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

Table 4

Putrescine modified peptides in bovine serum albumin that are labeled by the action of microbial transglutaminase.

BSA peptide	Labeled residue	Polyamine	Signature ions, Da	Discriminant score
GLVLIAFSQY	Q53	Putrescine		4.75
IAFSQYLQQCPFDEHVK	Q57	Putrescine		6.97
LIAFSQYLQQCPFDEHVK	Q57	Putrescine		6.52
GLVLIAFSQYLQQCPFDEH	Q57	Putrescine		6.90
GLVLIAFSQYLQQCPFDEHVKVK	Q57	Putrescine		4.41
YNGVFQECCQAEDK	Q193	Putrescine		6.45
YICDNQDTISSK	Q291	Putrescine	155	6.57
PENLPPLTADFAEDKDVCKNYQEAK	Q343	Putrescine		8.63
HLVDEPQNLIK	Q408	Putrescine		5.79
HLVDEPQNLIKQNCDQFEK	Q413	Putrescine		9.01
LGEYGFQNAL	Q427	Putrescine	200	5.20
GEYGFQNALIVR	Q427	Putrescine	129, 155, 200	6.52
LGEYGFQNALIVR	Q427	Putrescine	155, 200	8.21
VPQVSTPTLVEVSR	Q440	Putrescine		6.64
PDTEKQIK	Q545	Putrescine	155, 200	6.06
TLPDTEKQIK	Q545	Putrescine		5.63
TFHADICTLPDTEKQIK	Q545	Putrescine		5.85
KQTALVELLK	Q549	Putrescine	155	4.68
LVVSTQTAL	Q603	Putrescine	155	5.58

Cysteines are carbamidomethylated, adding 57 Da to the mass of the peptide. A discriminant score greater than 0.0 is considered to be strong evidence for a correct match of the peptide sequence to the MS/MS spectrum [11].