Abstract
I-cell (MLII) fibroblasts have a high free-cystine (cys) content. As in cystinotic (C) cells, the cys is in lysosomes. In cystine-free media with 1mM cysteamine, both cell types lose 50% of their cys in 6-9 min. The rate of loss changes with time, and by 60 min the decrease of cys is 88-97% in C cells but only 54-64% in MLII cells. Following removal of cysteamine and replacement with complete medium, cys reaccumulation in the first 8 h.is much greater in C cells (0.27-0.48 nmol/mg prot/h.) than in MLII cells (0.02-0.04 nmol/mg/h.). From 8 to 24 h. the rates of reaccumulation of both cell types are similar (0.06 nmol/mg/h.). Reaccumulation of cys in complete medium containing 30 mM glutathione-cysteine disulfide (GSSC) is increased 380% in C cells, but only 140% in MLII cells. With 50 μM chloroquine, the reaccumulation of cys in complete medium is inhibited in both cell types. Chloroquine does not inhibit the marked increase in cys reaccumulation with GSSC seen in C cells, but does in MLII cells. This suggests that the mechanism of cystine storage differs in the two cell types and that protein degradation is a more important source of cys in MLII than in C cells.
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