FIGURE 1. Expected structure of functional unit of L-type amino acid transporter. Human 4F2 heavy chain (CD98; h4F2hc), type II membrane glycoprotein, has molecular weight of approximately 80 kDa. This protein facilitates transport of ¹²⁵I-IMT by forming heterodimer by disulfide bond with light chain. Light chain has molecular weight of approximately 40 kDa. Human LAT1 and hLAT2 (light chains) have putative 12 transmembrane domains. Complementary DNAs of these transporters have been cloned.