ANALYSIS OF A BIOACTIVE SYNTHETIC ANALOG OF TUFTSIN BY TANDEM MASS-SPECTROMETRY - ANOMALOUS FAST-ATOM-BOMBARDMENT ACTIVATED PROCESSES

Fast atom bombardment (FAB) tandem mass spectrometry has been used to analyse the biologically potent, partially modified retro-inverso (PMR I) synthetic isomer of tuftsin: this compound represents the active pe ptide of the fraction of gamma-globulin (leukokinin) which binds speci fically to blood neutrophilic leukocytes and monocytes. Protonated mol ecules and fragment ions were collisionally dissociated at low energie s in a triple-quadrupole mass spectrometer to yield a complete picture of the reactions that occur in the condensed and in the gas phase. Th e study shows that, when retro-inversion is within the N-terminal amin o acid, charge localization at the basic sites (possibly at the N-term inus) induces a marked decomposition of the molecule, the loss of ammo nia being the most favourable fragmentation process. Also, artifacts a re formed in the liquid phase via bimolecular reactions promoted by th e high-energy beam. The findings indicate that despite the fact that P MRI isomers of this type are stable against exo-peptidases and also st able under acidic conditions, they appear to be labile under condition s where the energy deposition, due to FAB is necessarily high.