Uptake of L-cystine by brush-border membrane vesicles isolated from rat renal-cortical tissue was time-dependent and occurred in the absence of cystine reduction. A significant capacity for vesicular binding of cystine was observed. The amount bound increased with time of incubation and could be displaced by thiol reagents. At early time points, cystine uptake measured the transport of cystine into the intravesicular space. Total cystine uptake was mediated by multiple transport systems, including a low-Km high-affinity component which was shared by lysine, arginine, ornithine and glutamine and on which hetero-exchange diffusion of lysine and cystine was demonstrated.
