DEACETYLATION OF MERCAPTURIC ACIDS BY THE RABBIT, RAT AND GUINEA PIG* By H. G. BRAY

The results of Bray, Franklin & James (1959) suggest that the guinea pig cannot acetylate S-substituted L-cysteines as readily as can the rabbit or the rat. Since the failure to demonstrate acetylation might have been due to the presence of an active deacetylating system (cf. Krebs, Sykes & Bartley, 1947) we have investigated the excretion by the rabbit, rat and guinea pig of some administered mercapturic acids and the effect of preparations of liver and kidney on these compounds. Bray, James, Thorpe & Wasdell (1950) found that extracts of guinea-pig liver deacetylated N-acetylglycine more readily than did extracts of rabbit or rat liver, although the activities of extracts of guinea-pig and rabbit kidney were the same and greater than those of extracts of rat kidney. Marsden & Young (1958) found that about 33% of a dose of 1-naphthyl-[35S]mercapturic acid was excreted unchanged by rats, but, since the neutral sulphur fraction of the urine of these animals contained 81-89% of the radioactivity administered, they suggested that the urine contained some S-(1-naphthyl)-L-cysteine formed by metabolic deacetylation of the mercapturic acid. Parke & Williams (1951) reported that rabbits excreted 45% of a dose of phenylmercapturic acid unchanged and 14% as S-phenyl-L-cysteine, but their method of determination was not recorded.