Effect of L-tryptophan injection in rats on some enzymes of amino acid metabolism in liver. I. In vitro studies of the effect of L-tryptophan and its metabolites on the extramitochondrial L-alanine: 2-ketoglutaric aminotransferase.
Fed and fasted rats were injected with L-tryptophan (12.5 mg/100 g body weight) and the specific activities of L-glutamic: NAD oxidoreductase (deaminating) (EC 1.4.1.2) (GDH), L-aspartic-2-ketoglutaric aminotransferase (EC 2.6.1.1) (GOT) and L-alanine-2-ketoglutaric aminotransferase (EC 2.6.1.2) (GPT) from hepatic mitochondria and cytosol were compared. L-tryptophan results in a decrease of mitochondrial GDH activity by 22% and of cytosolic GPT and GOT by 42% and 38% respectively in the liver of fasted rats. Xanthurenate is a potent inhibitor of purified extramitochondrial GPT, whereas anthranilate and quinolinate are less potent inhibitors. L-tryptophan, 5-OH-tryptophan and indole exert a slight inhibition. Kynurenine, 5-OH-tryptamine, tryptamine, picolinic acid, nicotinic acid and indoloacetic acid do not show any inhibition of GPT. It is suggested that L-tryptophan injection inhibits extramitochondrial GPT by its transformation to xanthurenate and anthranilate.
D000410:Alanine Transaminase / Q000037:antagonists & inhibitors*; D000818:Animals; D001219:Aspartate Aminotransferases / Q000037:antagonists & inhibitors*; D005943:Gluconeogenesis / Q000187:drug effects; D005969:Glutamate Dehydrogenase / Q000037:antagonists & inhibitors*; D008099:Liver / Q000201:enzymology*; D008297:Male; D011805:Quinolinic Acids / Q000494:pharmacology; D051381:Rats; D014364:Tryptophan / Q000494:pharmacology*; D014977:Xanthurenates / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D011805:Quinolinic Acids; D014977:Xanthurenates; D062367:ortho-Aminobenzoates; D014364:Tryptophan; D005969:Glutamate Dehydrogenase; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase