Effect of L-Tryptophan Injection in Rats on Some Enzymes of Amino Acid Metabolism in Liver

A. Katsos; H. Philippidis; G. Palaiologos

doi:10.1055/s-2007-1019180

Hormone and Metabolic Research, Table of Contents

Horm Metab Res 1981; 13(2): 85-88
DOI: 10.1055/s-2007-1019180

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 AminotransferaseA. Katsos, H. Philippidis, G. Palaiologos

Department of Biological Chemistry, Medical School, University of Athens, Goudi, Athens, Greece

Abstract

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Summary

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-aspatic-2-ketoglutaric aminotransferase (EC 2.6.1.1.) (GOT) and L-alanine-2-ketoglutaric amino-transferase (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.

Key-Words:

L-Tryptophan and its Metabolites - GPT - GOT - GDH - Rat Liver Gluconeogenesis

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