Abstract
Normal leucocyte lysosomal membranes are able to transport cystine by a saturable process exhibiting efflux (T) and Counter-transport (CT). Leucocyte lysosomes from cystinotic patients lack this carrier mediated transport and thus store cystine. In order to establish whether T and CT are mediated by the same site, the effect of proteolytic enzymes, ATP, different H+ concentrations and N-Ethyl-Maleimid (NEM) on these two activities were examined. T and CT were measured in lysosome rich granular fractions extracted from normal PMN leucocytes loaded with cystine. Protease inhibited CT of cystine by 80% but did not influence the rate of cystine efflux. Trypsin and Chymotrypsin had no effect on both T and CT. ATP (2mM) and NEM (10mM) inhibited CT by 35% and 50% respectively. Cystine efflux was enhanced by 50% by ATP and not effected by NEM. Lowering the proton gradient across the membrane by incubating the lysosomes in an acidic medium (PH 5.5) caused an inhibition of both T and CT of cystine.
The observation that the two processes have different characteristics, yet both of them lack in cystinosis suggests that cystine T and CT occur at two different sites on a single protein carrier of the leucocyte lysosomal membrane.
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Bashan, N., Lorber, T., Potashnik, R. et al. CHARACTERISATION OF A TRANSPORT SYSTEM FOR CYSTINE IN LEUCOCYTES LYSOSOMAL MEMBRANES. Pediatr Res 19, 1074 (1985). https://doi.org/10.1203/00006450-198510000-00038
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DOI: https://doi.org/10.1203/00006450-198510000-00038
