Difference in Tryptophan-nicotinamide Conversion According to Dietary Nitrogen Sources; Casein, Casein Hydrolysate,...

We investigated whether the fate of tryptophan (Trp) to nicotinamide (Nam) is changeable according to nitrogen sources or not. Male rats were fed with a nicotinic acid-free diet (Trp content was arranged at about 234mg/100g of diet) containing casein, casein hydrolysates, or mixtures of amino acids (simulating the amino acid pattern of casein) for 12 days. From the urinary excretion of Nam and its metabolites, the conversion ratio was calculated. The conversion ratio was lower in the groups fed with the casein hydrolysate diets than in the groups fed with the casein and amino acid diets. In order to find the reason, the urinary excretion of kynurenic acid, xanthurenic acid, anthranilic acid, and 3-hydroxyanthranilic acid from the upper part of the Trp-Nam conversion pathway, the contents of free Trp in whole blood, and eight kinds of enzyme activities involved in the Trp-Nam pathway were measured. From these results, it is considered that the reason why the conversion ratio was lower in the casein hydrolysate group is due to the lower concentration of free Trp in whole blood and the higher activity of aminocarboxymuconate-semialdehyde decarboxylase. As is known that this enzyme activity is induced by adrenal cortical hormone, it was suggested that the release of this hormone is stimulated by feeding the casein hydrolysate diet.