Biochim Biophys Acta 2000 Dec 20;15091-2:7-13. doi: 10.1016/s0005-2736(00)00349-7.

Structure and function of ATA3, a new subtype of amino acid transport system A, primarily expressed in the liver and skeletal muscle.

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To date, two different transporters that are capable of transporting alpha-(methylamino)isobutyric acid, the specific substrate for amino acid transport system A, have been cloned. These two transporters are known as ATA1 and ATA2. We have cloned a third transporter that is able to transport the system A-specific substrate. This new transporter, cloned from rat skeletal muscle and designated rATA3, consists of 547 amino acids and has a high degree of homology to rat ATA1 (47% identity) and rat ATA2 (57% identity). rATA3 mRNA is present only in the liver and skeletal muscle. When expressed in Xenopus laevis oocytes, rATA3 mediates the transport of alpha-[(14)C](methylamino)isobutyric acid and [(3)H]alanine. With the two-microelectrode voltage clamp technique, we have shown that exposure of rATA3-expressing oocytes to neutral, short-chain aliphatic amino acids induces inward currents. The amino acid-induced current is Na(+)-dependent and pH-dependent. Analysis of the currents with alanine as the substrate has shown that the K(0. 5) for alanine (i.e., concentration of the amino acid yielding half-maximal current) is 4.2+/-0.1 mM and that the Na(+):alanine stoichiometry is 1:1.

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Species referenced: Xenopus laevis
Genes referenced: slc38a1 slc38a2 slc38a4