Cloning and Characterization of a Brain-specific Cationic Amino Acid Transporter

• Published in: The Journal of biological chemistry 1997-03, Vol.272 (13), p.8717-8722
• Main Authors: Hosokawa, Hiroshi, Sawamura, Tatsuya, Kobayashi, Shigeo, Ninomiya, Haruaki, Miwa, Soichi, Masaki, Tomoh
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acid Transport Systems, Basic; Amino Acids - metabolism; Animals; Arginine - metabolism; Base Sequence; Biological Transport; Blotting, Northern; Brain Chemistry; Carrier Proteins - chemistry; Carrier Proteins - genetics; Cloning, Molecular; COS Cells; Enzyme Inhibitors - pharmacology; Lysine - metabolism; Membrane Proteins - chemistry; Membrane Proteins - genetics; Molecular Sequence Data; Nitric Oxide Synthase - antagonists & inhibitors; Ornithine - metabolism; Potassium - metabolism; Rats; RNA, Messenger - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.13.8717

rCAT3 (at ationic mino acid ransporter 3), a cDNA that encodes a novel member of the murine CAT family was isolated. The protein encoded by rCAT3 contained 619 amino acids, 53-58% of which were identical with those of the murine CAT family proteins previously described (mouse CAT1, CAT2a, CAT2b, and rat CAT1). Transient expression of rCAT3 and L-[14C]arginine incorporation experiments in COS7 cells verified a high affinity system y+ transporter activity of rCAT3. First, rCAT3-mediated L-[14C]arginine incorporation was time-dependent and saturable with half-saturation constant (Km) values of 103 ± 12 μM (mean ± S.E., n = 3). Second, the incorporation was specific for cationic amino acids as evidenced from the inhibition by L-arginine, L-lysine, and L-ornithine. Third, neither sodium nor chloride ions in the extracellular medium were required for the activity. Fourth, the incorporation was inhibited by high potassium-induced membrane depolarization. On Northern blot using RNAs from various rat tissues, the expression of rCAT3 mRNA was restricted to the brain. These results indicated a role of rCAT3 in the system y+ transporter activity in the nervous tissue.