Isoform 1 functions as low-affinity, high capacity permease involved in the transport of the cationic amino acids (arginine, lysine and ornithine). Isoform 2 also functions as permease that mediates the transport of the cationic amino acids (arginine, lysine and ornithine), but it has much higher affinity for arginine than isoform 1. May play a role in classical or alternative activation of macrophages via its role in arginine transport. Detected in liver (at protein level) (PubMed:8385111). Highest expression in liver and T-cells. Also expressed in brain and lung. By macrophage activation. N-glycosylated. Affinity of isoform 2 for arginine uptake is 70-fold higher than for isoform 1. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Cationic amino acid transporter (CAT) (TC 2.A.3.3) family.