These clearly support another sequence. However this sequence is much less probable since, unlike structure 4, few additional supporting ions were identified. Only seven ions in Table V are consistent with the alternative, and only two other ions were found which uniquely support the alternative.We conclude that with the submolecular group approach, which conveniently permits the utilization of more of the available information, the sequencing of small peptides and other sequence molecules by mass spectrometry should gain a new level of reliability. The submolecular group method seems especially well suited to structural analyses of mixtures of small peptides where the possibility of finding multiple sequences is particularly high (9).
ACKNOWLEDGMENTWe thank Professor M. Bodanszky of Case-Western Reserve University for the protected peptide sample and Professor Harry Morrison of Purdue for the sample from his research program.
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