DIFFERENTIATION OF LYSINE GLUTAMINE IN PEPTIDE SEQUENCE-ANALYSIS BY ELECTROSPRAY-IONIZATION SEQUENTIAL MASS-SPECTROMETRY COUPLED WITH A QUADRUPOLE ION-TRAP/

Electrospray ionization coupled to a quadrupole ion trap mass spectrom eter is used to differentiate between the isobaric amino acids lysine and glutamine in sequence analysis of peptides. Collision-induced diss ociation is used for fragmentation. Several isobaric peptides with one or more lysines or glutamines at different positions were investigate d. The ambiguous amino acid either in the peptide chain or at the C- o r N-terminus can be clearly identified based on specific side chain fr agment ions resulting from MS3 or MS4 of B- and Y ''-fragment ions. (C ) 1998 John Wiley & Sons, Ltd.