Gas-Phase Conformation-Specific Photofragmentation of Proline-Containing Peptide Ions

Singly-protonated proline-containing peptides with N-terminal arginine are photodissociated with vacuum ultraviolet (VUV) light in an ESI linear ion trap/orthogonal-TOF (LIT/o-TOF). When proline is the n(th) residue from the N-terminus, unusual b(n) + 2 and a(n) + 2 ions are observed. Their formation is explained by homolytic cleavage of the C-alpha - C bond in conjunction with a rearrangement of electrons and an amide hydrogen. The latter is facilitated by a proline-stabilized gas-phase peptide conformation. (J Am Soc Mass Spectrom 2010, 21, 1455-1465) (C) 2010 American Society for Mass Spectrometry