A COMPARISON OF THE PEPTIDE FRAGMENTATION OBTAINED FROM A REFLECTOR MATRIX-ASSISTED LASER DESORPTION-IONIZATION TIME-OF-FLIGHT AND A TANDEM4-SECTOR MASS-SPECTROMETER

The types, extent, and overall distribution of peptide fragmentation p roduced by matrix-assisted laser desorption-ionization-postsource deca y (MALDI-PSD) on a reflector time-of-flight mass spectrometer were com pared with those obtained from high and low energy collision-induced d issociation (CID) on a four-sector mass spectrometer and from liquid s econdary ion mass spectrometry (LSIMS) ion source fragmentation and LS IMS metastable ion (MI) decomposition on a two-sector mass spectromete r. The model peptides studied had sequences and compositions that yiel ded predominantly either N- or C-terminal fragmentation from CID. For des-Arg(1) and des-Arg(9) bradykinin (i.e., H-PPGFSPFR-OH and H-RPPGFS PF-OH, respectively), the types of fragment ions and the extent to whi ch each type is formed in both MALDI-PSD and low energy CID spectra ar e remarkably similar. This observation suggests that both methods depo sit comparable internal energies (IE) into [M + H](+) precursor ions. The distribution of N-terminal, C-terminal, immonium, and internal fra gmentation from MALDI-PSD spectra of des-Arg(1) and des-Arg(9) bradyki nin did not change dramatically with respect to the terminal arginine position, contrary to those from LSIMS MI decomposition, high and low energy CID spectra. This observation in combination with the prominent immonium, internal, and minus 17 fragment ion types in PSD indicates that the imparted IE from MALDI and the 14 mu s of flight time may pro mote steady-state decomposition kinetics. Fragmentation distributions of MALDI-PSD spectra are also similar to those in LSIMS spectra. This implies that the distribution of protonation sites in [M + H](+) is co mparable for both techniques.