title: Impaired clearance of free cystine from lysosome-enriched granular fractions of I-cell-disease fibroblasts.
abstract: Cultured fibroblasts from patients with I-cell disease (mucolipidosis II) accumulate excessive amounts of free cystine, similarly to cells from patients with nephropathic cystinosis, a disorder of lysosomal cystine transport. To clarify whether the intralysosomal accumulation of cystine in I-cell-disease fibroblasts was due to a defective disposal mechanism, we measured the rates of clearance of free [35S]cystine from intact normal, cystinotic and I-cell-disease fibroblasts. Loss of radioactivity from the two mutant cell types occurred slowly (t 1/2 = 500 min) compared with the rapid loss from normal cells (t 1/2 = 40 min). Lysosome-rich granular fractions isolated from three different cystine-loaded normal, cystinotic and I-cell-disease fibroblast strains were similarly examined for non-radioactive cystine egress. Normal granular fractions lost cystine rapidly (mean t 1/2 = 43 min), whereas cystinotic granular fractions did not lose any cystine (mean t 1/2 = infinity). I-cell-disease granular fractions displayed prolonged half-times for cystine disposal (mean = 108 min), suggesting that I-cell-disease fibroblasts, like cystinotic cells, possess a defective carrier mechanism for cystine transport.
mesh_terms: D002478:Cells, Cultured; D003553:Cystine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D003554:Cystinosis / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D009081:Mucolipidoses / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D003553:Cystine; C034582:cystine dimethyl ester