Relationship between L-tryptophan uptake and L-tryptophan 2,3-dioxygenase activity in rat hepatocytes.
The relationship between L-tryptophan uptake and tryptophan 2,3-dioxygenase activity in hepatocytes was examined and compared with the change of hepatic L-leucine, L-phenylalanine, and L-tyrosine uptakes using isolated hepatocytes of rats in which the oxygenase was induced with L-tryptophan or hydrocortisone. In L-tryptophan- or hydrocortisone-treated rat hepatocytes, the rate of L-tryptophan uptake into hepatocytes via the saturable high-affinity transport component significantly increased but the hepatic uptake rate of L-leucine did not change at all. In hydrocortisone-treated rat hepatocytes, a little stimulated hepatic uptake of L-phenylalanine or L-tyrosine was observed. In the stimulated hepatic uptake of L-tryptophan via the high-affinity transport component, the Km value did not change but the Vmax value increased. Liver plasma membranes prepared from rats treated with L-tryptophan or hydrocortisone showed the same binding rate of L-tryptophan to the membranes as those from control rats. In addition, hepatic L-tryptophan uptake via the high-affinity transport component correlated well with hepatic tryptophan 2,3-dioxygenase activity (r = 0.787). The present results indicate that the uptake of L-tryptophan into hepatocytes via a transport system which works under physiological conditions is closely related to hepatic tryptophan 2,3-dioxygenase activity.
Saito
K
K
Department of Biochemistry, School of Medicine, Fujita-Gakuen Health University, Aichi.
Ohta
Y
Y
Nagamura
Y
Y
Sasaki
E
E
Ishiguro
I
I
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D006854:Hydrocortisone / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D010649:Phenylalanine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014364:Tryptophan / Q000378:metabolism*; D014366:Tryptophan Oxygenase / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D014366:Tryptophan Oxygenase; D007930:Leucine; D006854:Hydrocortisone