DERIVATIZATION TO ENHANCE SEQUENCE-SPECIFIC FRAGMENTATION OF PEPTIDESAND PROTEINS

Results are presented that demonstrate that the guanidination of lysin e residues of peptides and proteins can enhance the sequence-specific fragmentation observed in Cf-252-plasma desporption mass spectrometry. The conversion of the lysine residue(s) of [Lys1] bradykinin, recombi nant eglin C, and ribonuclease A to homoarginine resulted in increased fragment ion peak intensities and the formation of additional fragmen t ion containing the homoarginine residue(s). This enhancement in the fragmentation of peptides and proteins is achieved by replacing sites with moderate proton affinity, the side chains of lysines, with more b asic sites, the guanidino groups of homoarginine residues, increasing protonation and thus, fragment ion formation. Formation of molecular i ons was not strongly affected by guanidination. In addition to enhanci ng fragmentation, the guanidination of lysine residues provides a simp le way to distinguish lysine from glutamine residues using mass spectr ometry.