title: Cysteamine depletes cystinotic leucocyte granular fractions of cystine by the mechanism of disulphide interchange.
abstract: Cystinotic lysosome-rich leucocyte granular fractions, loaded with [35S]cystine, were exposed to different cystine-depleting agents. During a 30 min incubation at 37 degrees C, untreated cystinotic granular fractions lost negligible [35S]cystine when corrected for lysosome rupture. Granular fractions exposed to 0.1 mM-cysteamine lost 64% of their initial cystine, and hexosaminidase activity was decreased by 10%. This was accompanied by the formation of high concentrations of [35S]cysteine-cysteamine mixed disulphide within the granular-fraction pellet, and, in the presence of N-ethylmaleimide, increasing amounts of [35S]cysteine-N-ethylmaleimide adduct outside the granular fraction. In separate experiments, [35S]cystine exited cystinotic leucocyte lysosomes at a negligible rate (half-times 199 and 293 min), but [35S]cysteine-cysteamine mixed disulphide exhibited substantial egress (half-times 66 and 88 min) and was recovered intact outside the granular-fraction pellet. We conclude that cysteamine depletes lysosomes of cystine by participating in a thiol-disulphide interchange reaction to produce cysteine and cysteine-cysteamine mixed disulphide, both of which traverse the cystinotic leucocyte lysosomal membrane.
mesh_terms: D003538:Cystamine / Q000378:metabolism; D003543:Cysteamine / Q000494:pharmacology*; D003553:Cystine / Q000378:metabolism*; D003554:Cystinosis / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D006207:Half-Life; D006801:Humans; D007962:Leukocytes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D004220:Disulfides; D003553:Cystine; D003543:Cysteamine; D005033:Ethylmaleimide; D003538:Cystamine