Sequence-ion enhancement of peptides digested with proteinase K

Proteinase K has been employed to proteolyze peptides before their mass spectrometric analysis. This combination of the two methods yields abundant sequence ions in the mass spectrum, thus leading to an easy prediction of the primary structure of the peptide. It was found that both the variety of available sequence ions and also their abundances are increased strongly after proteinase K digestion, when compared with the normal mass spectrum. The shortcoming of little fragmentation encountered using conventional mass spectrometric ionization methods can mostly be overcome. The H'n and Y"m ions produced from proteolysis provided a double check of the peptide sequence.