| Abstract: | We have cloned a new subtype of theamino acid transport system N2 (SN2 or second subtype of system N) fromrat brain. Rat SN2 consists of 471 amino acids and belongs to therecently identified glutamine transporter gene family that consists ofsystem N and system A. Rat SN2 exhibits 63% identity with rat SN1. Italso shows considerable sequence identity (50-56%) with themembers of the amino acid transporter A subfamily. In the rat, SN2 mRNA is most abundant in the liver but is detectable in the brain, lung,stomach, kidney, testis, and spleen. When expressed in Xenopus laevis oocytes and in mammalian cells, rat SN2 mediatesNa+-dependent transport of several neutral amino acids,including glycine, asparagine, alanine, serine, glutamine, andhistidine. The transport process is electrogenic, Li+tolerant, and pH sensitive. The transport mechanism involves the influxof Na+ and amino acids coupled to the efflux ofH+, resulting in intracellular alkalization. Proline, -(methylamino)isobutyric acid, and anionic and cationic amino acidsare not recognized by rat SN2. |
