The metabolism of S-methyl-L-cysteine.

1. Methylsulphinylacetic acid, 2-hydroxy-3-methylsulphinylpropionic acid and methylmercapturic acid sulphoxide (N-acetyl-S-methyl-l-cysteine S-oxide) were isolated as their dicyclohexylammonium salts from the urine of rats after they had been dosed with S-methyl-l-cysteine. 2. A fourth sulphoxide was isolated but not identified. 3. The excretion of sulphate in the urine of rats dosed with S-methyl-l-cysteine was measured. 4. The metabolism of S-methyl-l-cysteine by the hamster and guinea pig was examined chromatographically. 5. The preparation of the following compounds is reported: (-)-dicyclohexylammonium methyl-mercapturate sulphoxide; the dicyclohexylammonium salts of the optically inactive forms of 2-hydroxy-3-methylthiopropionic acid, 2-hydroxy-3-methyl-sulphinylpropionic acid and methylsulphinylacetic acid.