The cationic amino acid transporter (CAT) family is comprised of four homologous membrane proteins: CAT-1, CAT-2, CAT-3 and CAT-4, encoded by the Slc7A1−4 genes, respectively. The major difference between these transporters is at the level of tissue specificity and regulation of their expression.The CAT family is included in the Na+-independent transport system, (named system y+) that mediate L-arginine uptake in most tissues and cells.n CAT-2 is known to transport cationic amino acids such as L-arginine, L-ornithine, and L-lysine. It is considered to be the major arginine transporter in most cells and tissues.It can be expressed in two spliced variants, CAT-2A and CAT-2B. CAT-2A, is a low-affinity transporter, constitutively expressed in the liver and muscle cells, whereas CAT-2B, is a high-affinity transporter, abundantly expressed in macrophages