Abstract
AbstractSequence 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 the sequence information of the spectra.
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