title: Mode of L-tryptophan uptake into rat hepatocytes via trypsin-sensitive high-affinity transport system.
abstract: The effect of trypsin treatment on the mode of L-tryptophan uptake (L- and T-transport systems) into hepatocytes was investigated in comparison with that of L-leucine (L-type system) using isolated rat hepatocytes. L-Tryptophan uptake occurred via at least two saturable (one high-affinity and one low-affinity) and one non-saturable components in intact hepatocytes, while L-leucine was taken up via one saturable and one non-saturable component. Hepatocytes whose surface had been digested with trypsin lost only the high-affinity component of the two saturable L-tryptophan transport systems, while they retained the saturable component for L-leucine transport (Km = 3.3 mM). Km values for the trypsin-sensitive (high-affinity) and -insensitive (low-affinity) components of L-tryptophan uptake were 14 microM and 2.1 mM, respectively. However, inhibition studies with some substrates of the L-, T- and both transport systems as inhibitor demonstrated that L-tryptophan uptake via these two components could not be classified in terms of the T- and L-systems. The present results indicate the presence of a carrier with a very high affinity for L-tryptophan in rat hepatocytes.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D066298:In Vitro Techniques; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014357:Trypsin / Q000494:pharmacology*; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D014364:Tryptophan; D014357:Trypsin; D007930:Leucine