[Membrane transport system of amino acids in the small intestine]

The membrane transport system of amino acids in the small intestine is reviewed. Amino acids are transported by three processes: 1) simple diffusion, 2) facilitated diffusion and 3) active transport. In the brush border membrane, there are at least six Na(+)-dependent systems (NBB, PHE, IMINO, beta, X-G,A, Y+) and the Na(+)-independent systems (L, beta, Y+). On the other hand, the basolateral membrane has at least four Na(+)-dependent systems (A, ASC, X-G,A, N) and three Na(+)-independent systems (asc, L, y+). These systems are discussed.