Optimization of carbamylation conditions and study on the effects on the product ions of carbamylation and dual modification of the peptide by Q-TOF MS.

Modified peptides fragmented by collision-induced dissociation can offer additional sequence information, which is beneficial for the de novo sequencing of peptides. Here, the model peptide VQGESNDLK was carbamylated. The optimal conditions were as follows: temperature of 90℃, pH of 7, and the time of 60 min. Then, we studied the b- and y-series ions of the native, carbamylated, and dual-modified peptides. The results were as follows. The short carbamylated peptides (≤10 amino acid residues) produced more b-series ions (including b1 ion). The long carbamylated peptides (>10 amino acid residues) produced additional b1 ion but fewer y-series ions (especially in the high-mass region). The short dual-modified peptides produced more b-series ions (including b1 ion) and more y-series ions, and their peptide sequence coverage was almost 100%. The long dual-modified peptides produce b1 ion and more y-series ions, and their peptide sequence coverage was nearly above 90%. Therefore, both carbamylation and the dual modification method could be used to identify the N-terminal amino acid, and the dual modification method was also excellent for the de novo sequencing of the tryptic peptides.