Abstract: By the sulfonation at the N-terminal of peptides, the charge state of histidine-containing peptides is different from that of other peptides in pH<3.0 solution. Based on this difference, a new method was developed to isolate and identify sulfonated histidine-containing peptides from tryptic digest of proteins by strong cation exchange (SCX) chromatography and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF MS/MS). Using the standard proteins containing histidines as the model, the methodology was evaluated. The results show that sulfonated histidine-containing peptides were efficiently enriched by SCX, and the N-terminal sulfonation of the peptides simplifies the interpretation of the acquired mass spectra and facilitates the sequencing of histidine-containing peptides by producing consecutive and predominant ions in positive mode MS2 spectra, which is thought to be the result of the charge neutralization of b ions by the N-terminal sulfonic acid group. The discrimination of b ions and y ions can greatly enhance the confidence in peptide and subsequent protein identification. It is feasible to isolate and enrich the histidine-containing peptides by using this method which has the potential applications in proteomics.

Key words: enrichment, histidine-containing peptides , identification, matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF MS/MS), sulfonation modification, strong cation exchange chromatography （SCX）