SLC6A15 functions as a sodium-dependent neutral amino acid transporter. It exhibits preference for the branched-chain amino acids, particularly leucine, valine and isoleucine and methionine. SLC6A15 mediates the saturable, pH-sensitive and electrogenic cotransport of proline and sodium ions with a stoichiometry of 1:1. It may have a role as transporter for neurotransmitter precursors into neurons. In contrast to other members of the neurotransmitter transporter family, SLC6A15 does not appear to be chloride-dependent [taken from the Universal Protein Resource (UniProt) www.uniprot.org/uniprot/Q9H2J7].