Negative ion fragmentations of deprotonated peptides containing post-translational modifications: diphosphorylated systems containing Ser, Thr and Tyr. A characteristic phosphate/phosphate cyclisation. A joint experimental and theoretical study
Date
2009
Authors
Andreazza, H.
Wang, T.
Bilusich, D.
Hoffmann, P.
Bowie, J.
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Rapid Communications in Mass Spectrometry, 2009; 23(12):1825-1833
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Hayley J. Andreazza, Tianfang Wang, Daniel Bilusich, Peter Hoffmann and John H. Bowie
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Abstract
[M-H](-) anions from small diphosphopeptides (phosphate groups on Ser, Thr or Tyr) show characteristic peaks corresponding to m/z 177 (H(3)P(2)O(7)(-)), 159 (HP(2)O(6)(-)) and sometimes [(M-H)(-)-H(4)P(2)O(7)](-). M/z 1.77 and m/z 1.59 are major peaks in the spectra of small peptides with 1,2, 1,3, 1,4, 1,5 and 1,6 diphosphate substitution, which means that the decomposing [M-H](-) anions must have flexible structures in order for the two phosphate groups to interact with each other. Peptides where the two phosphate groups are more than six amino acid residues apart have not been studied. Theoretical calculations indicate that m/z 1.77 is formed in a strongly exothermic reaction involving facile nucleophilic interaction between the two phosphate groups: m/z 159 is formed by loss of water from energised m/z 177.
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Copyright 2009 John Wiley & Sons