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Side‐chain radical losses from radical cations allows distinction of leucine and isoleucine residues in the isomeric peptides Gly‐XXX‐Arg
Author(s) -
Wee Sheena,
O'Hair Richard A. J.,
McFadyen W. David
Publication year - 2002
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.658
Subject(s) - chemistry , isoleucine , protonation , stereochemistry , leucine , electrospray ionization , ion , fragmentation (computing) , dissociation (chemistry) , side chain , radical ion , crystallography , peptide , amino acid , organic chemistry , biochemistry , polymer , computer science , operating system
Sequencing of peptides via low‐energy collision‐induced dissociation of protonated peptides typically yields b n and y n sequence ions. The isomeric residues leucine and isoleucine rarely can be distinguished in these experiments since they give b n and y n sequence ions of the same m/z . Siu's pioneering work on electrospray ionization of copper complexes of peptides (Chu IK, Rodriquez CF, Lau TC, Hopkinson AC, Siu KWM. J. Phys. Chem. B 2000; 104: 3393) provides a way of forming radical cations of peptides in the gas phase. This method was used to generate M +· ions of the two isomeric peptides Gly‐Leu‐Arg and Gly‐Ile‐Arg in order to compare their fragmentation reactions. Both radical cations fragment to give even electron y 2 and y 1 sequence ions as well as side‐chain radical losses of CH 3 and CH 3 CH 2 for isoleucine and (CH 3 ) 2 CH for leucine. In contrast the [M + H] + and [M + 2H] 2+ ions do not allow distinction between the isomeric leucine and isoleucine peptides. Copyright © 2002 John Wiley & Sons, Ltd.