Metabolism of L-cysteine in guinea pig liver.

The metabolism of L-cysteine in guinea pig liver was studied. Guinea pig liver contained 0.45 +/- 0.05 (mean +/- SD) mumol of cysteine, 0.180 +/- 0.080 mumol of 3-mercaptolactate-cysteine disulfide [S-(2-hydroxy-2-carboxyethylthio)cysteine, HCETC], and 8.082 +/- 0.516 mumol of reduced glutathione per g of fresh tissue. The taurine content was 0.912 +/- 0.158 mumol per g of fresh liver. Cysteine dioxygenase (EC 1.13.11.20) activity was several-fold lower than cysteine aminotransferase (EC 2.6.1.3) activity. Lactate dehydrogenase (EC 1.1.1.27) activity was about 10-fold higher than 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) activity. These results indicate that the oxidative metabolism of L-cysteine in the guinea pig liver is not as active as in the rat liver and that L-cysteine, at least in part, is metabolized via the transaminative pathway, in which 3-mercaptopyruvate is partly reduced to 3-mercaptolactate and is utilized to form HCETC.