Characteristics of cystine counter-transport in normal and cystinotic lysosome-rich leucocyte granular fractions.
Normal leucocyte lysosome-rich granular fractions exhibited counter-transport of cystine, confirming that cystine transport across the lysosomal membrane is carrier-mediated. The trans-activation of cystine transport was temperature-dependent but relatively independent of the external Na+ or K+ concentration in phosphate buffer. Counter-transport, measured as uptake of exogenous [3H]cystine, increased with increasing intralysosomal cystine content up to approx. 3 nmol of half-cystine/unit of hexosaminidase activity. The amount of [3H]cystine entering lysosomes loaded with unlabelled cystine decreased when unlabelled cystine was added to the extralysosomal medium. Lysosomal cystine counter-transport was stereospecific for the L-isomer. Cystathionine, cystamine and cysteamine-cysteine mixed disulphide gave evidence of sharing the lysosomal cystine-transport system, although at lower activity than cystine. Other tested amino acids, including arginine, glutamate and homocystine, were inactive in this system. Nine leucocyte lysosome-rich preparations from eight different cystinotic patients displayed virtually no counter-transport of cystine, conclusively establishing that a carrier-mediated system for cystine transport is dysfunctional in cystinotic lysosomes.
D000596:Amino Acids / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D003553:Cystine / Q000097:blood* / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007962:Leukocytes / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D003553:Cystine; D012964:Sodium; D011188:Potassium