The relation between thiamine, biotin and tryptophan metabolism, studied in the rat

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Abstract
The metabolism of tryptophan was studied in rats deficient in thiamine, thiamine and pyridoxine, biotin, and biotin and pyridoxine. When thiamine deficiency was imposed on pyridoxine-deficient rats, and supplementary tryptophan was fed, the metabolite-excretory pattern typical of pyridoxine deficiency was abolished or much reduced. Formation of the substrates of the kynureninase reaction was therefore inhibited. Kynurenine fed at the same stage produced a marked metabolite excretion. No formylkynurenine was excreted on giving tryptophan to rats with a simple thiamine deficiency. Hence thiamine is concerned in the conversion of tryptophan into formylkynurenine. Similar tests of combined biotin and pyridoxine deficiencies suggest that biotin is probably not concerned in any stage of the conversion of tryptophan into hydroxykynurenine. Considerable advantages were found in giving vitamins by stomach-tube rather than by mixing them in the diet.