Amino Acid Transport in Suspension-Cultured Plant Cells : III. COMMON CARRIER SYSTEM FOR THE UPTAKE OF l-ARGININE, l-ASPARTIC ACID, l-HISTIDINE, l-LEUCINE, AND l-PHENYLALANINE.

The transport of l-arginine (l-Arg), l-aspartic acid (l-Asp), l-histidine (l-His), and l-phenylalanine (l-Phe) has been investigated in suspension cultures of Nicotiana tabacum cv. Wisconsin 38 cells. Uptake of these amino acids is pH- and energy-dependent, concentrative (except for l-Asp), stereospecific, dependent upon culture growth phase, and, apparently, carrier-mediated. A 1,000-fold higher concentration of l-leucine (l-Leu) can inhibit all of the energy-dependent uptake of l-Arg, l-Asp, l-His, and l-Phe. A 1,000-fold higher concentration of l-Arg or l-Phe can inhibit all of the energy-dependent uptake of l-Leu. l-Asp and l-His cannot inhibit all of the energy-dependent l-Leu uptake. However, evidence is presented which indicates that l-Leu enters the cell via the carrier system which also transports l-Asp and l-His. These inhibition data are consistent with the hypothesis that all of these amino acids are transported by a single carrier system.