Metabolism of cysteine and cysteinesulfinate in rat and cat hepatocytes.

The metabolism of cysteine and cysteinesulfinate was studied in freshly isolated hepatocytes from fed rats and cats. In incubations of rat hepatocytes with cysteinesulfinate, the rate of hypotaurine plus taurine production was approximately the same as the rate of conversion of the 1-carbon of cysteinesulfinate to CO2. In contrast, no significant production of hypotaurine plus taurine occurred in incubations of cat hepatocytes with cysteinesulfinate. These data are consistent with the species difference in the activity of hepatic cysteinesulfinate decarboxylase, which converts cysteinesulfinate to hypotaurine. In incubations of either rat or cat hepatocytes with cysteine, no hypotaurine plus taurine production was detected. However, the 1-carbon of cysteine was converted to CO2 and the production of urea plus ammonia nitrogen was significantly increased over the rates observed in incubations of cells without substrate. Our results suggest that most cysteine oxidation by hepatocytes occurs by pathways that do not involve formation of cysteinesulfinate.