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

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Abstract
Fed and fasted rats were injected with L-tryptophan (12.5 mg/100 g body wt) 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; 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 IAA do not show any inhibition of GPT. L-tryptophan injection apparently inhibits extramitochondrial GPT by its transformation to xanthurenate and anthranilate.

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