Metabolism of l-cysteine via transamination pathway (3-mercaptopyruvate pathway)

T. Ubuka, J. Ohta, R. Akagi, Y. Hosaki, Y. Ishimoto, S. Kiguchi, T. Ikeda, K. Ishino

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15 Citations (Scopus)


We have studied the transamination pathway (3-mercaptopyruvate pathway) of l-cysteine metabolism in rats. Characterization of cysteine aminotransferase (EC from liver indicated that the transamination, the first reaction of this pathway, was catalyzed by aspartate aminotransferase (EC 3-Mercaptopyruvate, the product of the transamination, may be metabolized through two routes. The initial reactions of these routes are reduction and transsulfuration, and the final metabolites are 3-mercaptolactate-cysteine mixed disulfide [S-(2-hydroxy-2-carboxyethylthio)cysteine, HCETC] and inorganic sulfate, respectively. The study using anti-lactate dehydrogenase antiserum proved that the enzyme catalyzing the reduction of 3-mercaptopyruvate was lactate dehydrogenase (EC Formation of HCETC was shown to depend on low 3-mercaptopyruvate sulfurtransferase (EC activity. Results were discussed in relation to HCETC excretion in normal human subjects and patients with 3-mercaptolactate-cysteine disulfiduria. Incubation of liver mitochondria with l-cysteine, 2-oxoglutarate and glutathione resulted in the formation of sulfate and thiosulfate, indicating that thiosulfate was formed by transsulfuration of 3-mercaptopyruvate and finally metabolized to sulfate.

Original languageEnglish
Pages (from-to)243-252
Number of pages10
JournalAmino Acids
Issue number3
Publication statusPublished - Oct 1 1992


  • 3-Mercaptolactate-cysteine mixed disulfide
  • 3-Mercaptopyruvate pathway
  • Amino acids
  • Cysteine metabolism
  • Cysteine transamination
  • Sulfate formation

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry
  • Organic Chemistry


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