The relation between pyridoxin and tryptophan metabolism, studied in the rat

Abstract

On admn. of tryptophan to rats on a low pyridoxine diet numerous metabolites appear in the urine. The probable identity of the majority of these was established. A convenient method for group isolation involved precipitation by mercuric acetate in acid soln. and selective adsorption on deactivated charcoal. The scope of Ehrlich''s and Ekman''s and other reagents was studied, and chromatographic, chemical, spectroscopic and certain other properties of the metabolites were recorded. Besides the previously known L-kynurenine, kynurenic acid and xanthurenic acid, the occurrence of L-3-hydroxykynurenine as a tryptophan metabolite was demonstrated. Na-Acetyl derivatives of both L-kynurenine and L-3-hydroxykynurenine were excreted. These compounds may be normal metabolic intermediates. In addition, L-3-hydroxy-kynurenine is excreted with the phenol group conjugated as the glycuronide and sulphate. The occurrence of conjugated derivatives of kynurenic and xanthurenic acids was demonstrated. The fact that all these metabolites retain the C atoms of the original alanine side chain of tryptophan provides strong chemical evidence that pyridoxine participates in tryptophan metabolism at the stage at which this side chain is split from the rest of the molecule. Alternative metabolic pathways for tryptophan are discussed and it is suggested that 3,4-dihydroxykynurenine is unlikely to be a tryptophan metabolite of major importance.