Quantitative determination of methionine in proteins: gas chromatography of methylthiocyanate liberated by cleavage with cyanogen bromide.

A rapid non hydrolytic method was developed for the estimation of methionine residues in peptides and proteins. The method is based on the gas chromatographic determination of methylthiocyanate liberated in the reaction of cyanogen bromide with the methionine residues. In contrast to the amino acid analyzer technique this method allows selective determination of methionine in the presence of methionine sulphoxide and sulphone. It was tested with both purified proteins and protein-containing crude samples (legume seeds) and was compared with different analyzer techniques.