Component of several heterodimeric complexes involved in amino acid transport (PubMed:9915839). The precise substrate specificity depends on the other subunit in the heterodimer (PubMed:9915839). The complexes function as amino acid exchangers (By similarity). The homodimer functions as sodium-independent, high-affinity transporter that mediates uptake of large neutral amino acids such as phenylalanine, tyrosine, L-DOPA, leucine, histidine, methionine and tryptophan (PubMed:9915839). The heterodimer formed by SLC3A2 and SLC7A6 or SLC3A2 and SLC7A7 mediates the uptake of dibasic amino acids (By similarity). The heterodimer with SLC7A5/LAT1 mediates the transport of thyroid hormones triiodothyronine (T3) and thyroxine (T4) across the cell membrane (By similarity). The heterodimer with SLC7A5/LAT1 is involved in the uptake of toxic methylmercury (MeHg) when administered as the L-cysteine or D,L-homocysteine complexes (By similarity). The heterodimer with SLC7A5/LAT1 is involved in the uptake of leucine (By similarity). When associated with LAPTM4B, the heterodimer with SLC7A5/LAT1 is recruited to lysosomes to promote leucine uptake into these organelles, and thereby mediates mTORC1 activation (By similarity). The heterodimer with SLC7A5/LAT1 may play a role in the transport of L-DOPA across the blood-brain barrier (Probable). The heterodimer formed by SLC3A2 and SLC7A5/LAT1 or SLC3A2 and SLC7A8/LAT2 is involved in the cellular activity of small molecular weight nitrosothiols, via the stereoselective transport of L-nitrosocysteine (L-CNSO) across the transmembrane (By similarity). Together with ICAM1, regulates the transport activity of SLC7A8/LAT2 in polarized intestinal cells by generating and delivering intracellular signals (By similarity). Required for targeting of SLC7A5/LAT1 and SLC7A8/LAT2 to the plasma membrane and for channel activity (PubMed:9915839). Plays a role in nitric oxide synthesis in human umbilical vein endothelial cells (HUVECs) via transport of L-arginine (By similarity). May mediate blood-to-retina L-leucine transport across the inner blood-retinal barrier (By similarity). Disulfide-linked heterodimer with a non-glycosylated light chain (SLC7A5, SLC7A6, SLCA7A7, SLC7A8, SLC7A10 or SLCA7A11) (PubMed:9915839, PubMed:10574970, PubMed:11011012). Interacts with TLCD3A/CT120 and ICAM1. Constitutively and specifically associates with beta-1 integrins (alpha-2/beta-1, alpha-3/beta-1, alpha-5/beta-1 and alpha-6/beta-1), but minimally with alpha-4/beta-1. Interacts with LAPTM4B; recruits SLC3A2 and SLC7A5 to lysosomes to promote leucine uptake into these organelles and is required for mTORC1 activation (By similarity). Localized at the plasma membrane when associated with SLC7A5 or SLC7A8. Localized to the apical membrane of placental syncytiotrophoblastic cells. Recruited to lysosomes by LAPTM4B (By similarity). Located selectively at cell-cell adhesion sites (PubMed:9915839). Colocalized with SLC7A8/LAT2 at the basolateral membrane of kidney proximal tubules and small intestine epithelia. Expressed in both luminal and abluminal membranes of brain capillary endothelial cells (By similarity). Detected on the surface of embryonic epithelial cells in the epidermis, thymus, kidney, intestine, brain choroid plexus, and in retina. Detected in adult and embryonic brain, spleen, kidney, intestine and liver, and in adult testis (at protein level) (PubMed:9915839). Observed in all adult tissues tested with strongest expression in kidney, small intestine, spleen, thymus and liver (PubMed:9915839). Moderate expression in brain, stomach, heart, testis, lung, skin, pancreas and skeletal muscle. In brain expressed on capillary endothelia in cerebral cortex. Strong expression in the liver of 14 dpc embryo and in brain, spleen, liver, kidney and intestine of an 18 dpc embryo. Expression induced by concanavalin-A stimulation. Induced during cell activation but is subsequently maintained at constant levels throughout the cell cycle in exponentially growing cells. Phosphorylation on Ser-300 or Ser-302 and on Ser-420 by ecto-protein kinases favors heterotypic cell-cell interactions. Leucine uptake was inhibited by ileum, valine histidine and phenylalanine as well as by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) (a specific inhibitor of system L transport). Belongs to the SLC3A transporter family. Truncated N-terminus.