Isolation of (−) S-Methyl-L-Cysteine from Beans ( Phaseolus vulgaris )

THE recent isolation 1,2 of S-methyl- L -cysteine sulphoxide from two crucifers, turnips and cabbage, and the chromatographic evidence 3 for its occurrence in many related plants suggested the possibility that methyl cysteine should also occur in plants. In addition, preliminary evidence has clearly indicated that the turnip can readily form the sulphoxide from methyl cysteine. A careful examination 3 of the protein and non-protein fractions of several crucifers revealed no methyl cysteine. Previous work 4 on the non-protein amino-acids of bean seeds showed a ninhydrin-reactive spot which gave an iodoplatinate test 5 indicative of the sulphur amino-acids. This material was found on a two-directional chromatogram (phenol: butanol–acetic acid) in a position corresponding to that of methyl cysteine and close to that of γ-amino-butyric acid. This compound has been isolated and identified as (−) S-methyl- L -cysteine.