title: Cystine metabolism in human fibroblasts. Comparison of normal, cystinotic, and gamma-glutamylcysteine synethetase-deficient cells.
abstract: Incubation of normal human skin fibroblasts or fibroblasts derived from patients with erythrocyte deficiency of gamma-glutamylcysteine synthetase (gamma-glutamylcysteine synthetase-deficient) in culture medium containing L-[35S]cystine resulted in incorporation of radioactivity into protein, cysteine, and glutathione, gamma-Glutamylcysteine synthetase-deficient fibroblasts synthesized glutathione from [35S]cystine at 30% the rate of normal cells and contained 30% the normal amount of glutathione. Cystinotic fibroblasts incorporated [35S]cystine into the large intracellular cystine pool not found in normal or gamma-glutamylcysteine synthetase-deficient cells and also appeared to synthesize glutathione more slowly than normal cells. However, the radioactivity recovered as cystine was reduced greatly and the rate of [35S]cystine incorporation into glutathione increased if cystinotic cells were first depleted of their intracellular cystine pool before incubation in [35S]cystine. This suggests that the apparent reduced rate of glutathione synthesis observed in untreated cystinotic cells was a secondary effect caused by dilution of the [35S]cystine by the large pool of nonradioactive cystine. Cystinotic cells depleted of cystine by treatment with mercaptoethylamine reaccumulate 30 to 50% of their initial cystine in 24 hours in the absence of extracellular cystine. Both normal and cystinotic cells lose more than 90% of their intracellular glutathione in 24 hours in cystine-free medium. Both cell types can reutilize cysteine from glutathione for protein synthesis.
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000378:metabolism*; D002478:Cells, Cultured; D003553:Cystine / Q000378:metabolism*; D003554:Cystinosis / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D010453:Peptide Synthases / Q000097:blood / Q000172:deficiency*; D012867:Skin / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D013439:Sulfhydryl Reagents; D003553:Cystine; D010453:Peptide Synthases