Negative ion fragmentations of deprotonated peptides: backbone cleavages directed through both Asp and Glu |
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Authors: | Brinkworth C S Dua S McAnoy A M Bowie J H |
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Affiliation: | Department of Chemistry, The University of Adelaide, South Australia 5005, Australia. |
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Abstract: | The collision-induced spectra of [M - H](-) ions of a variety of natural and synthetic amphibian peptides containing Asp and/or Glu exhibit characteristic gamma backbone cleavage ions that identify the positions of these residues in the peptide. A theoretical study suggests that the Glu cleavage involves an S(N)i reaction of the carboxylate anion from the Glu alpha side chain to form a deprotonated cyclic lactone. The presence of either Asp or Glu or other residues that effect pronounced side-chain cleavages (e.g. Ser or Thr) results in the normal alpha and beta backbone cleavages being reduced in comparison to those cleavages which originate from side chains. |
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