The metabolism of S-propylcysteine in the rat has been re-investigated. The previously known major metabolite has been isolated and identified as the mercapturic acid, N-acetyl-S-propylcysteine. 2. Several further metabolites have been isolated from the urine of rats treated with S-propyl[35S]cysteine. These have been identified as S-propylcysteine-S-oxide, N-acetyl-S-(2-hydroxypropyl)cysteine, S-(propylthio)lactate, S-(2,3-dihydroxypropyl)cysteine and N-acetyl-S-(2-carboxyethyl)cysteine. 3. The metabolism of S-(2-hydroxypropyl)-, S-(3-hydroxypropyl)- and S-(2,3-dihydroxypropyl)-[35S]cysteine have been investigated in the rat. The results, integrated with those from the metabolism of S-propyl[35S]cysteine, have enabled the pathways of S-propylcysteine to be deduced. 4. The oxidative metabolism of a number of S-alkyl cysteines is discussed.
