Functions as permease involved in the transport of the cationic amino acids (arginine, lysine and ornithine); the affinity for its substrates differs between isoforms created by alternative splicing. Isoform 1 functions as permease that mediates the transport of the cationic amino acids (arginine, lysine and ornithine), and it has much higher affinity for arginine than isoform 2. Isoform 2 functions as low-affinity, high capacity permease involved in the transport of the cationic amino acids (arginine, lysine and ornithine) (PubMed:9174363). May play a role in classical or alternative activation of macrophages via its role in arginine transport. Expressed at high levels in the skeletal muscle, placenta and ovary. Expressed at intermediate levels in the liver and pancreas and at low levels in the kidney and heart. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Cationic amino acid transporter (CAT) (TC 2.A.3.3) family. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.