title: Metabolism ofL-cysteine via transamination pathway (3-mercaptopyruvate pathway).
abstract: We have studied the transamination pathway (3-mercaptopyruvate pathway) ofL-cysteine metabolism in rats. Characterization of cysteine aminotransferase (EC 2.6.1.3) from liver indicated that the transamination, the first reaction of this pathway, was catalyzed by aspartate aminotransferase (EC 2.6.1.1). 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 1.1.1.27). Formation of HCETC was shown to depend on low 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) activity. Results were discussed in relation to HCETC excretion in normal human subjects and patients with 3-mercaptolactate-cysteine disulfiduria. Incubation of liver mitochondria withL-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.
authors.affiliation: Department of Biochemistry, Okayama University Medical School, 2-5-1 Shikatacho, 700, Okayama, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ubuka
authors.forename: J
authors.initials: J
authors.lastname: Ohta
authors.forename: R
authors.initials: R
authors.lastname: Akagi
authors.forename: Y
authors.initials: Y
authors.lastname: Hosaki
authors.forename: Y
authors.initials: Y
authors.lastname: Ishimoto
authors.forename: S
authors.initials: S
authors.lastname: Kiguchi
authors.forename: T
authors.initials: T
authors.lastname: Ikeda
authors.forename: K
authors.initials: K
authors.lastname: Ishino