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 tubule. Disulfide-linked heterodimer with the amino acid transport protein SLC3A1. Interacts with CAV1. Kidney and small intestine. Belongs to the amino acid-polyamine-organocation (APC) superfamily.