Cellular transport in the regulation of amino acid metabolism.

In mammalian cells, the intracellular levels of the neutral amino acids are regulated to meet the nutritional needs of the cells. The cellular levels of the amino acids are maintained by balancing the uptake of amino acids from the extracellular medium and the biosynthesis of certain of the amino acids, with the requirements of the cell for amino acids for protein synthesis and energy metabolism. The uptake of the neutral amino acids is carried out by several distinct transport systems, which differ in their reactivities with substrates. ions and inhibitors. The transport systems have been characterized kinetically and, more recently, these studies have included the characterization of the regulation of transport.