title: The glutathione dependence of inorganic sulfate formation from L- or D-cysteine in isolated rat hepatocytes.
abstract: The GSH dependence of the metabolic pathways involved in the conversion of cysteine to sulfate in intact cells has been investigated. It was found that hepatocyte-catalysed sulfate formation from added L-cysteine did not occur if hepatocyte GSH was depleted beforehand, but was restored when GSH levels recovered. Furthermore, sulfate formation did not recover in GSH-depleted hepatocytes if GSH synthesis was prevented with buthionine sulfoximine. Thiosulfate formation was, however, markedly enhanced in GSH-depleted hepatocytes. These results suggest that thiosulfate is an intermediate in the formation of inorganic sulfate from L-cysteine and that GSH was required for the conversion of thiosulfate to inorganic sulfate. Much less sulfate was formed if the cysteine was replaced with cysteinesulfinate. Furthermore, sulfate formation from L-cysteine was markedly inhibited by the addition of the transaminase inhibitor DL-cycloserine or the gamma-cystathionase inhibitor DL-propargylglycine. The major routes of sulfate formation from L-cysteine therefore seems to involve pathways that do not involve L-cysteinesulfinate. Similar amounts of sulfate were formed from D-cysteine as L-cysteine. Thiosulfate instead of sulfate was also formed in GSH-depleted hepatocytes. However, sulfate formation from D-cysteine differed from L-cysteine in that it was inhibited by the D-aminoacid oxidase inhibitor sodium benzoate and was not affected by transaminase or gamma-cystathionase inhibitors. These results suggest that thiosulfate is an intermediate in sulfate formation from D-cysteine and involves the oxidation of D-cysteine by D-amino acid oxidase to form beta-mercaptopyruvate.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Huang
authors.forename: S
authors.initials: S
authors.lastname: Khan
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000480:Alkynes / Q000494:pharmacology; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D019817:Benzoic Acid; D019328:Buthionine Sulfoximine / Q000494:pharmacology*; D002478:Cells, Cultured; D003486:Cyanides / Q000494:pharmacology; D003523:Cycloserine / Q000494:pharmacology; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D018377:Neurotransmitter Agents; D051381:Rats; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism; D013431:Sulfates / Q000378:metabolism*; D013885:Thiosulfates / Q000032:analysis / Q000378:metabolism
chemical_list: D000480:Alkynes; D001565:Benzoates; D003486:Cyanides; D018377:Neurotransmitter Agents; D013431:Sulfates; D013885:Thiosulfates; D019328:Buthionine Sulfoximine; C008366:3-mercaptopyruvic acid; C009055:propargylglycine; D019817:Benzoic Acid; D003523:Cycloserine; D005978:Glutathione; D003545:Cysteine; D005998:Glycine; C013461:cysteine sulfinic acid