Tryptophan metabolism in vitamin B6-deficient mice.
Vitamin B6 deficiency was induced in mice by maintenance for 4 weeks on a vitamin B6-free diet. Tryptophan metabolism was assessed by determining the urinary excretion of tryptophan metabolites, the metabolism of [14C]tryptophan in vivo and the formation of tryptophan and niacin metabolites by isolated hepatocytes. The vitamin B6-deficient animals excreted more xanthurenic acid and 3-hydroxykynurenine, and less of the niacin metabolites N1-methyl nicotinamide and methyl-2-pyridone-4-carboxamide, than did control animals maintained on the same diet supplemented with 5 mg vitamin B6/kg. After intraperitoneal injection of [14C]tryptophan, vitamin B6-deficient mice showed lower liberation of 14CO2 from [methylene-14C]tryptophan and [U-14C]tryptophan than did controls, indicating impairment of kynureninase (EC 3.7.1.3) activity. There was no difference between the two groups of animals in the metabolism of [ring-2-14C]tryptophan. Hepatocytes isolated from the vitamin B6-deficient animals formed more 3-hydroxykynurenine and xanthurenic acid than did cells from control animals, but also formed more NADP and free niacin.
Bender
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Department of Biochemistry, University College and Middlesex School of Medicine, London.
Njagi
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Danielian
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D000409:Alanine / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D005561:Formates / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D014364:Tryptophan / Q000378:metabolism*; D026681:Vitamin B 6 Deficiency / Q000378:metabolism* / Q000652:urine; D015430:Weight Gain / Q000502:physiology
D005561:Formates; C030544:formic acid; D014364:Tryptophan; D000409:Alanine