Effect of tryptophan metabolites on the activities of rat liver pyridoxal kinase and pyridoxamine 5-phosphate oxidase in vitro.
Pyridoxal kinase was purified 4760-fold from rat liver. The Km values for pyridoxine and pyridoxal were 120 and 190 microM respectively, and pyridoxine showed substrate inhibition at above 200 microM. Pyridoxamine 5-phosphate oxidase was also purified 2030-fold from rat liver, and its Km values for pyridoxine 5-phosphate and pyridoxamine 5-phosphate were 0.92 and 1.0 microM respectively. Pyridoxine 5-phosphate gave a maximum velocity that was 5.6-fold greater than with pyridoxamine 5-phosphate and showed strong substrate inhibition at above 6 microM. Among the tryptophan metabolites, picolinate, xanthurenate, quinolinate, tryptamine and 5-hydroxytryptamine inhibited pyridoxal kinase. However, pyridoxamine 5-phosphate oxidase could not be inhibited by tryptophan metabolites, and on the contrary it was activated by 3-hydroxykynurenine and 3-hydroxyanthranilate. Regarding the metabolism of vitamin B-6 in the liver, the effects of tryptophan metabolites that were accumulated in vitamin B-6-deficient rats after tryptophan injection were discussed.
Takeuchi
F
F
Tsubouchi
R
R
Shibata
Y
Y
D000818:Animals; D007700:Kinetics; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D008297:Male; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D010848:Picolinic Acids / Q000494:pharmacology; D011731:Pyridoxal Kinase / Q000302:isolation & purification / Q000378:metabolism*; D011734:Pyridoxaminephosphate Oxidase / Q000302:isolation & purification / Q000378:metabolism*; D017378:Quinolinic Acid; D011805:Quinolinic Acids / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014363:Tryptamines / Q000494:pharmacology; D014364:Tryptophan / Q000378:metabolism*; D014977:Xanthurenates
D010848:Picolinic Acids; D011805:Quinolinic Acids; D014363:Tryptamines; D014977:Xanthurenates; C028330:xanthurenic acid; D014364:Tryptophan; D011734:Pyridoxaminephosphate Oxidase; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010770:Phosphotransferases; D011731:Pyridoxal Kinase; D017378:Quinolinic Acid; D007736:Kynurenic Acid; C030614:picolinic acid