Sodium-independent, high affinity transport of small neutral D- and L-amino acids and amino acid-related compounds. May play a role in the modulation of glutamatergic transmission through mobilization of D-serine at the glutamatergic synapse (By similarity). Disulfide-linked heterodimer with the amino acid transport protein SLC3A2/4F2hc. Belongs to the amino acid-polyamine-organocation (APC) superfamily.