Involved in the high-affinity sodium-independent transport of cystine and neutral and dibasic amino acids (system B(0,+)-like activity). May function as an activator of SLC7A9 and be involved in the high-affinity reabsorption of cystine in the kidney proximal tubule. Disulfide-linked heterodimer with the amino acid transporter SLC7A9. Predominantly expressed in kidney and intestine. In kidney localized to the apical membrane of the proximal tubules.