Amino acid-proton symporter. Stereospecific transporter with a broad specificity for histidine, arginine, glutamate and neutral amino acids, favoring small amino acids such as alanine, asparagine and glutamine. Accepts also large aromatic residues such as in phenlalanine or tyrosine. Has a much higher affinity for basic amino acids as compared with AAP1. May function in xylem-to-phloem transfer and in uptake of amino acids assimilated in the green silique tissue. Inhibited by diethylpyrocarbonate (DEPC). Optimum pH is acidic. Highly expressed in developing pods. Found in the vascular strands of siliques, cotyledons, leaves and roots, in the inner phloem of stems, and in the funiculi. Lower levels of expression in flowers. Not expressed in seeds. Strongly induced at heart stage of embryogenesis. Belongs to the amino acid/polyamine transporter 2 family. Amino acid/auxin permease (AAAP) (TC 2.A.18.2) subfamily.