Phenyl thiocarbamoyl and related derivatives of peptides: Edman chemistry in the gas phase

Formation of the b(1) ion during the low energy collision-activated dissoci ation of the N-terminal phenyl thiocarbamoyl (PTC) derivatives of protonate d peptides is analogous to the condensed-phase cleavage step of the Edman d egradation. Previous studies confined to the analysis of tryptic peptides a re here extended to probe the influence of peptide structure and extent of protonation on the prevalence of this fragmentation. The data are consisten t with a requirement for protonation of the peptide backbone at the N-termi nal amide linkage. Generally, PTC derivatives of peptides that incorporate as many or more basic amino acid residues than charges fail to undergo favo red cleavage of the N-terminal amide bond, reflecting the absence of a prot on resident on the peptide backbone to promote such fragmentation. Exceptio ns to this rule may be explained in terms of proton bridging between basic sites to release an ionizing proton for residence on the peptide backbone. Replacement of the PTC derivative by the pentafluoro-PTC analog results in similar fragmentation chemistry but with preferential loss of the derivatiz ed N-terminal residue as a neutral fragment. Thus, judicious choice of deri vatization procedure enables not only the direction of fragmentation but al so of charge retention. (Int J Mass Spectrom 188 (1999) 95-103) (C) 1999 El sevier Science B.V.