The hetero and homo condensation of peptides resulting from the pyrolysis of peptides were observed by MS analysis of the non-volatile pyrolysis products. Tandem MS analyses demonstrated that intermolecular C-terminal to N- terminal bonding is favored during pyrolysis when forming the bond between two peptides, rather than involving basic and acidic side chain groups like arginine and aspartic acid. Further evidence of N-terminus to C-terminus condensation was provided by the pyrolysis of a standard N-acetylated peptide containing an internal arginine group, which did not form any detectable condensation product. Peptide condensation during pyrolysis of proteins and peptides has been shown to occur at pyrolysis temperatures between 180-300 deg C. Even though sequence information of the individual peptides involved in the condensation reaction is preserved, caution must be taken in analyzing sequence data derived from MS/MS analysis of condensation peptides as these result from permutated combinations of the reacting peptides, resulting in the scrambling of sections of the original peptide sequence [2]. The implementation of a multistage tandem MS analysis (e.g., MS~(3)) could circumvent this shortcoming by analyzing shorter fragments of the condensation peptide that would accurately correspond to a sequence of the original peptide.
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