LAT1 is a heterodimeric membrane transport protein that preferentially transports neutral branched (valine, leucine, isoleucine) and aromatic (tryptophan, tyrosine) amino acids. LAT is highly expressed in brain capillaries (which form the blood brain barrier) relative to other tissues.CD98 is a glycoprotein that comprises the light subunit of the Large neutral Amino acid Transporter (LAT1).

Kanai et al. (1998) used expression cloning to isolate a rat cDNA termed LAT1. They showed that LAT1 encoded a protein necessary for system L amino acid transport, thought to be a major route by which cells import large neutral amino acids with branched or aromatic side chains.