Metabolism of methyllabeled S-methylcysteine in the rat.

Evidence has recently been presented for the natural occurrence of S-methylcysteine in kidney bean seeds (2) and in Neurospora crassa (3). The sulfoxide of S-methylcysteine has also been shown to occur in relatively high concentrations in the nonprotein nitrogen fraction of turnips, cabbage, and several other crucifers (4, 5). It is also of interest that the peptide, y-glutamyl-Smethylcysteine, has been isolated from the seeds of various leguminous plants (6, 7). S-Methylcysteine can be degraded by various bacteria (8, 9), and synthesized by molds (3) and yeast extracts (10). The amino acid has not as yet been demonstrated as a naturally occurring compound in mammalian tissues, and it was found to be ineffective in restoring growth of rats (11) and rabbits (13) on a cystine-deficient diet. On the other hand, increases in total sulfate excretion have been noted when Smethylcysteine was fed to dogs (12) and rabbits (13). In view of the widespread occurrence of X-methylcysteine in plants, the possibility exists that S-methylcysteine may play an important role in the normal metabolic processes of plant and also animal tissues. The present investigation is concerned with determining the extent of oxidation of the methyl group to carbon dioxide and the degree of incorporation of the methyl carbon into tissue choline and creatine in the intact rat.