Sample derivatization and structure analysis by field desorption mass spectrometry. Peptide methylation-methanolysis

Analysis by field desorption mass spectrometry of reaction product mixtures produced by treatment of peptides with methanol and hydrogen chloride augments significantly structural data derived by direct field desorption mass spectrometry analysis of the peptides. Analyses of data obtained by three peptides, beta-Ala-HisOH, p-Glu-Ser-GlyOH and Glu-Ser-Gly-AspOH are used for illustration. Data from field desorption mass spectrometry of peptide methylation-methanolysis product mixtures are used to (a) distinguish [M]+- from [M + H]+ in peptide field desorption mass spectrometry spectra, (b) ascertain the number of carboxyl groups present in a peptide, (c) identify a pyro-glutamyl N-terminus and (d) derive peptide sequence information. Definitive assignments of ion relationships are facilitated by use of methanol and deuteromethanol in paired experiments.