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Identification and Functional Characterization of a Na+-independent Neutral Amino Acid Transporter with Broad Substrate Selectivity

Segawa, H ; Fukasawa, Y ; Miyamoto, K ; Takeda, E ; Endou, H ; Kanai, Y

The Journal of biological chemistry, 1999-07, Vol.274 (28), p.19745-19751 [Periódico revisado por pares]

United States: American Society for Biochemistry and Molecular Biology

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  • Título:
    Identification and Functional Characterization of a Na+-independent Neutral Amino Acid Transporter with Broad Substrate Selectivity
  • Autor: Segawa, H ; Fukasawa, Y ; Miyamoto, K ; Takeda, E ; Endou, H ; Kanai, Y
  • Assuntos: Amino Acid Sequence ; Amino Acid Transport Systems ; Amino Acids - metabolism ; Animals ; Antigens, CD - genetics ; Biological Transport ; Carrier Proteins - chemistry ; Carrier Proteins - genetics ; Cloning, Molecular ; Fusion Regulatory Protein-1 ; Hydrogen-Ion Concentration ; Intestine, Small - metabolism ; Kinetics ; Leucine - metabolism ; Membrane Proteins - chemistry ; Membrane Proteins - genetics ; Molecular Sequence Data ; Oocytes - metabolism ; Rats ; RNA, Complementary - genetics ; RNA, Messenger - metabolism ; Sequence Alignment ; Substrate Specificity ; Xenopus
  • É parte de: The Journal of biological chemistry, 1999-07, Vol.274 (28), p.19745-19751
  • Descrição: We have isolated a cDNA from rat small intestine that encodes a novel Na + -independent neutral amino acid transporter with distinctive characteristics in substrate selectivity and transport property. The encoded protein, designated L-type amino acid transporter-2 (LAT-2), shows amino acid sequence similarity to the system L Na + -independent neutral amino acid transporter LAT-1 (Kanai, Y., Segawa, H., Miyamoto, K., Uchino, H., Takeda, E., and Endou, H.(1998) J. Biol. Chem. 273, 23629–23632) (50% identity) and the system y + L transporters y + LAT-1 (47%) and KIAA0245/y + LAT-2 (45%) (Torrents, D., Estevez, R., Pineda, M., Fernandez, E., Lloberas, J., Shi, Y.-B., Zorzano, A., and Palacin, M. (1998) J. Biol. Chem. 273, 32437–32445). LAT-2 is a nonglycosylated membrane protein. It requires 4F2 heavy chain, a type II membrane glycoprotein, for its functional expression in Xenopus oocytes. LAT-2-mediated transport is not dependent on Na + or Cl − and is inhibited by a system l -specific inhibitor, 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), indicating that LAT-2 is a second isoform of the system L transporter. Compared with LAT-1, which prefers large neutral amino acids with branched or aromatic side chains, LAT-2 exhibits remarkably broad substrate selectivity. It transports all of the l -isomers of neutral α-amino acids. LAT-2 exhibits higher affinity ( K m = 30–50 μ m ) to Tyr, Phe, Trp, Thr, Asn, Ile, Cys, Ser, Leu, Val, and Gln and relatively lower affinity ( K m = 180–300 μ m ) to His, Ala, Met, and Gly. In addition, LAT-2 mediates facilitated diffusion of substrate amino acids, as distinct from LAT-1, which mediates amino acid exchange. LAT-2-mediated transport is increased by lowering the pH level, with peak activity at pH 6.25, because of the decrease in the K m value without changing the V max value. Because of these functional properties and a high level of expression of LAT-2 in the small intestine, kidney, placenta, and brain, it is suggested that the heterodimeric complex of LAT-2 and 4F2 heavy chain is involved in the trans -cellular transport of neutral amino acids in epithelia and blood-tissue barriers.
  • Editor: United States: American Society for Biochemistry and Molecular Biology
  • Idioma: Inglês
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