title: Transport of the aromatic amino acids into isolated rat liver cells. Properties of uptake by two distinct systems.
abstract: The transport of the aromatic amino acids into isolated rat liver cells was studied. There was a rapid and substantial binding of the aromatic amino acids, L-alanine and L-leucine to the plasma membrane. This has important consequences for the determination of rates of transport and intracellular concentrations of the amino acids. Inhibition studies with a variety of substrates of various transport systems gave results consistent with aromatic amino acid transport being catalysed by two systems: a 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH)-insensitive aromatic D- and L-amino acid-specific system, and the L-type system (BCH-sensitive). The BCH-insensitive component of transport was Na+-independent and facilitated non-concentrative transport of the aromatic amino acids; it was unaffected by culture of liver cells for 24 h, by 48 h starvation, dexamethasone phosphate or glucagon. Kinetic properties of the BCH-inhibitable component were similar to those previously reported for the L2-system in liver cells. The BCH-insensitive component was a comparatively low-Km low-Vmax. transport system that we suggest is similar to the T-transport system previously seen only in human red blood cells. The results are discussed with reference to the importance of the T- and L-systems in the control of aromatic L-amino acid degradation in the liver.
mesh_terms: D000596:Amino Acids / Q000378:metabolism* / Q000494:pharmacology; D000598:Amino Acids, Cyclic; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010649:Phenylalanine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014364:Tryptophan / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000598:Amino Acids, Cyclic; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D007930:Leucine