Metabolism of 3-mercaptopyruvate was investigated using homogenates of rat heart, liver and kidney. When 3-mercaptopyruvate was incubated with heart homogenate, L-cysteine, L-alanine, S-(2-hydroxy-2-carboxyethylthio)-L-cysteine and 3-mercaptolactate were produced. At the same time, a decrease in the amounts of L-glutamate and L-aspartate was demonstrated. These results indicate that 3-mercaptopyruvate was converted to L-cysteine by cysteine aminotransferase (EC 2.6.1.3), to 3-mercaptolactate by lactate dehydrogenase (EC 1.1.1.27), and to pyruvate by 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2), and that HCETC and L-alanine were formed from these products. In the presence of liver homogenate, 3-mercaptopyruvate was mainly metabolized by 3-mercaptopyruvate sulfurtransferase; production of L-cysteine was small and HCETC was not formed. The metabolism of 3-mercaptopyruvate in the presence of kidney homogenate was intermediate between heart and liver: a fair amount of L-cysteine was formed, but HCETC was not produced. A peak which corresponds to L-cysteine-glutathione disulfide on the chromatogram of amino acid analysis was present when 3-mercaptopyruvate was incubated with heart or liver homogenate, but not with kidney homogenate.</p
