Studies on the kynurenine adminotransferase activity in rat liver and kidney.
The kynurenine aminotransferase activity of supernatant and mitochondrial fractions obtained from rat liver and kidney was studied with L-kynurenine and L-3-hydroxykynurenine as substrates. A substrate inhibition with L-kynurenine at concentrations higher than 6-7mM was observed with all four enzyme preparations. This did not happen with L-3-hydroxykynurenine as a substrate. Moreover, the liver mitochondrial enzyme shows a Km for pyridoxal phosphate 2-4 times smaller than the other preparations when assayed with L-3-hydroxykynurenine as a substrate. Therefore, the accumulation of xanthurenic acid and not of kynurenic acid in B6 deficiency could be related both to this high activity of liver mitochondrial kynurenine aminotransferase with L-3-hydroxykynurenine, even at small concentrations of B6, and to substrate inhibition observed with L-kynurenine and not with L-3-hydroxykynurenine.
D000818:Animals; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology* / Q000648:ultrastructure; D007700:Kinetics; D007736:Kynurenic Acid / Q000378:metabolism; D007737:Kynurenine / Q000031:analogs & derivatives / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D011732:Pyridoxal Phosphate / Q000378:metabolism; D051381:Rats; D000637:Transaminases / Q000378:metabolism*; D014977:Xanthurenates / Q000378:metabolism
D014977:Xanthurenates; D007737:Kynurenine; D011732:Pyridoxal Phosphate; D000637:Transaminases; D007736:Kynurenic Acid