Associates with SLC3A1 to form a functional transporter complex that mediates the electrogenic exchange between cationic amino acids and neutral amino acids, with a stoichiometry of 1:1 (PubMed:16825196, PubMed:32494597, PubMed:32817565, PubMed:8663357). Has system b(0,+)-like activity with high affinity for extracellular cationic amino acids and L-cystine and lower affinity for intracellular neutral amino acids (PubMed:16825196, PubMed:32494597, PubMed:8663357). Substrate exchange is driven by high concentration of intracellular neutral amino acids and the intracellular reduction of L-cystine to L- cysteine (PubMed:8663357). Required for reabsorption of L-cystine and dibasic amino acids across the brush border membrane in renal proximal tubules. {ECO:0000269|PubMed:10471498, ECO:0000269|PubMed:10588648, ECO:0000269|PubMed:16609684, ECO:0000269|PubMed:16825196, ECO:0000269|PubMed:32494597, ECO:0000269|PubMed:32817565, ECO:0000269|PubMed:8663357}. This is the function of SLC7A9 (solute carrier family 7 member 9, ENSG00000021488).