Figure 5.

Cysteine but not glutamate or quisqualate inhibit Cya-EC-mediated ³⁵S-cystine uptake. Cells were treated with 25 μM ³⁵S-cystine alone or in the presence of 10 μM Cya-EC along with either 5 mM glutamate, 250 μM quisqualate, 5 mM cysteine or 5 mM cystine, added to the labeling mixture just before addition to the cells for 10 min. After solubilization of the cells in 0.2 M NaOH, aliquots were taken for scintillation counting and protein determination. Results are presented as the percent of uptake in the absence of glutamate, quisqualate, cysteine or cystine. Similar results were obtained in three independent experiments. * indicates significantly different from control.