Amino acid-proton symporter. Stereospecific transporter with a broad specificity for neutral amino acids, favoring small amino acids such as alanine, asparagine and glutamine. Accepts also large aromatic residues such as in phenlalanine or tyrosine. Inhibited by 2,4-dinitrophenol. Expressed in leaves, stems and flowers. High expression in source leaves, but almost undetected in sink leaves. Down-regulated by drought. Belongs to the amino acid/polyamine transporter 2 family. Amino acid/auxin permease (AAAP) (TC 2.A.18.2) subfamily.