Amino Acid Transporters

Amino acids support the normal physiological functions, including protein synthesis, cell growth, and homeostasis in the body. Amino acid transporters, which are plasma membrane proteins, belong to a class of specialized transporters that regulate the transport of amino acids across the plasma membrane. The specific transporters are located in apical and basolateral membranes of the intestinal and kidney epithelial cells to ensure the efficient vectorial transport of amino acids through the epithelia to the systemic circulation. There are various classification systems for amino acids, among which the classification systems based on similarities in transporter protein structures is more used. Additionally, most amino acid transporters are classified into transporters that can transport cationic, neutral, imino, and anionic amino acids. Another way to classify amino acid transporters is based on the role of Na+: Na+-dependent and Na+-independent transporters. In this chapter, we discuss the molecular features, transporter properties, and mechanisms of the multispecific nature of amino acid drug transporters, as well as implications related to absorption of drugs and regulation of the amino acid transporters. For the complex functions, protein conformation changes, and amino acid physiological stimulation of each amino acid transporter, we expect to see more advancement in the future.