Effects of Three Kinds of Dietary Nitrogen Sources on the Metabolic Fate of Tryptophan

We have recently reported that the conversion ratio of tryptophan to nicotinamide [urinary excretion of (nicotinamide + N1-methylnicotinamide (MNA)+ N1-methyl-2-pyridone-5-carboxamide (2-Py) + N1-methyl-4-pyridone-3-carboxamide (4-Py) (μmol/day)/tryptophan intake during urine collection (μmol/day)] was changeable according to the kind of dietary nitrogen sources. In these experiments, we investigated whether the fate of tryprophan is changeable according to nitrogen sources or not. Weanling rats were fed with a diet low in nitrogen (1.1311% nitrogen) containing a suitable amount of nicotinic acid (6 mg/100 g of diet) for 17 days. Egg white (EW), egg white proteolysate-5 (EWP-5), and mixture of amino acids simulating the amino acid pattern of EWP-5 were used as dietary nitrogen sources. The urinary excretion of 5-hydroxyindole-3-acetic acid and the sum of nicotinamide and its metabolites in the group fed with the EWP-5 diet was the lowest, but, the excretion ratio of (2-Py + 4-Py)/MNA, which has been repor...