Mj. Deery et al., A MECHANISM FOR THE LOSS OF 60 U FROM PEPTIDES CONTAINING AN ARGININERESIDUE AT THE C-TERMINUS, Journal of the American Society for Mass Spectrometry, 8(3), 1997, pp. 253-261
The loss of 60 u from protonated peptide ions containing an arginine r
esidue at the C-terminus has been investigated by means of low energy
tandem mass spectrometry. The lowest energy conformation of singly cha
rged bradykinin is thought to involve a salt-bridge structure, which m
ay lead to the formation of two isomeric forms. It is thought that one
isomer retains the ionizing proton at the C-terminal end of the pepti
de, leading to the formation of the [b(n-1) + H + OH](+) fragment ion,
and the other isomer retains the charge at the N-terminus, leading to
the formation of the [M + H - 60](+) fragment ion. It was found that
the formation of the [M + H - 60](+) ion occurs only from singly charg
ed precursor ions. In addition, the loss of 60 u occurs from peptides
in which the charge is localized at the N-terminus. These results indi
cate that the mechanism of formation of the [M + H - 60](+) ion may be
driven by a charge-remote process. (C) 1997 American Society for Mass
Spectrometry.