Sodium-dependent amino acid transporter. Mediates electrogenic symport of neutral amino acids and sodium ions. Has a broad specificity, with a preference for Ala, followed by Ser, His, Gly, Cys, Asn, Thr, Pro, Gln and Met. May mediate sodium-independent transport of cationic amino acids, such as Arg and Lys. Amino acid uptake is pH-dependent, with lower transport activities at pH 6.5, intermediate at pH 7.0 and highest between pH 7.5 and 8.5. Optimum pH is 7.5-8.5. Detected in liver, in hepatocytes surrounding the central vein. Not detected in heart, kidney, brain, lung, small intestine, spleen and thymus. The disulfide bond plays an important role in substrate transport, but has no effect on trafficking to the cell surface. Imprinted gene expressed from the paternal allele in blastocysts. Belongs to the amino acid/polyamine transporter 2 family.