Partial Methanolysis and Fast Atom Bombardment Mass Spectrometry of Peptides Containing Sulphurated Amino Acids

Article abstract of DOI:10.1002/oms.1210261018

Sequence determination by partial methanolysis and fast atom bombardment (FAB) mass spectrometry of peptides containing cysteine and methionine was investigated.Cysteine-containing peptides require methylation of the sulphydryl group by methyl iodide to give a stable S-methylcysteinyl residue prior to partial methanolysis and mass spectrometry.Methionine-containing peptides undergo partially a methylation on sulphur during methanolysis, with formation of an S-methylsulphonium ion which under FAB conditions is extracted from the matrix and eliminates methyl sulphide in the gas phase.The presence of additional peaks due to chemical modifications or gas-phase fragmentations, however, does not interfere with sequence information of the spectra.