Amino Acid Transport Disorders, Inborn: Disorders characterized by defective transport of amino acids across cell membranes. These include deficits in transport across brush-border epithelial cell membranes of the small intestine (MICROVILLI) and KIDNEY TUBULES; transport across the basolateral membrane; and transport across the membranes of intracellular organelles. (From Nippon Rinsho 1992 Jul;50(7):1587-92)Amino Acid Transport Systems: Cellular proteins and protein complexes that transport amino acids across biological membranes.Amino Acids: Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.Aminoisobutyric Acids: A group of compounds that are derivatives of the amino acid 2-amino-2-methylpropanoic acid.Amino Acid Transport Systems, Basic: Amino acid transporter systems capable of transporting basic amino acids (AMINO ACIDS, BASIC).Biological Transport: The movement of materials (including biochemical substances and drugs) through a biological system at the cellular level. The transport can be across cell membranes and epithelial layers. It also can occur within intracellular compartments and extracellular compartments.Amino Acid Transport System A: A sodium-dependent neutral amino acid transporter that accounts for most of the sodium-dependent neutral amino acid uptake by mammalian cells. The preferred substrates for this transporter system include ALANINE; SERINE; and GLUTAMINE.Biological Transport, Active: The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy.Amino Acid Transport System L: A sodium-independent neutral amino acid transporter system with specificity for large amino acids. One of the functions of the transporter system is to supply large neutral amino acids to the brain.