Involved in the high-affinity, sodium-independent transport of cystine and neutral and dibasic amino acids (system B(0,+)-like activity). Thought to be responsible for the high-affinity reabsorption of cystine in the kidney proximal tubule. Disulfide-linked heterodimer with the amino acid transport protein SLC3A1. Interacts with CAV1. Outer medulla of kidney (at protein level). Kidney and small intestine. In the kidney localized to the apical membrane of the proximal tubules. Belongs to the amino acid-polyamine-organocation (APC) superfamily.