Cystine accumulation in cystinotic fibroblasts from free and protein-linked cystine but not cysteine

Abstract
The accumulation of cystine in [human] cystinotic fibroblasts from free and protein-linked cystine was investigated. Cystine is not accumulated from cysteine but is readily accumulated from cystine. The accumulation from free cystine does not occur as a result of pinocytosis or from the degradation of a rapidly metabolized protein pool. Further studies of the degradation of S-S-containing proteins by these cells may aid understanding of the mechanisms of proteolysis.