Collision-induced fragmentation of (M + H) + ions of peptides. Side chain specific sequence ions

Abstract

The collision (10 keV)-induced decomposition (CID) of (M + H) + ions of peptides generated by fast atom bombardment ionization has been studied in a tandem mass spectrometer consisting of two consecutive double-focussing analyzers. Two novel fragmentation processes are described; one (termed d n ) leads to the formation of N-terminal ions that permit the differentiation of leucine isoleucine; the other leads to a new set of C-terminal ions (termed v n ) and is related to the structure of the amino acid representing the N-terminus of the fragment. The mechanisms of formation are supported by B 2/E and B/E scans, which define the precursor and product ions. These and other fragmentations of (M + H) + ions under CID conditions and kilovolt collision energies seem to involve fragmentation at a site remote from the charge. The fragmentation processes which (M + H) + ions of peptides undergo are related to the site of protonation and the degree to which the positive charge is fixed at that site.