Enzymes That Control the Conversion of L-Tryptophan-nicotinamide and the Urinary Excretion Ratio (N1-Methyl-2-pyridone-5-carboxamide plus N1-Methyl-4-pyridone-3-carboxamide)/N1-Methylnicotinamide in Mice

There is little information on L-tryptophan -> nicotinamide metabolism in mice. In the present study, we investigated the two important nutritional factors involved in metabolism L-tryptophan -> nicotinamide; one is the amount of nicotinamide synthesized from L-tryptophan, and the other is the urine ratio (N-1-methyl-2-pyridone-5-carboxamide + N-1-methyl-4-pyridone-3-carboxamide)/N-1-methylnicotinamide. The order of the percentages of nicotinamide synthesized from L-tryptophan was as follows: CBA strain mice (conversion percentage 0.41%) < BALB strain mice (0.82%) < C57BL/6 strain mice (1.13%) < ICR strain mice (1.70%). Urinary excretion of quinolinic acid was correlated with urinary excretion of the sum of nicotinamide and its catabolites (p <0.0001). The urine sum, which reflects the conversion of L-tryptophan -> nicotinamide, correlated well with the activity of 3-hydroxyanthranilic acid dioxygenase (p = 0.040). A nutritional indicator, the urine ratio (N-1-methyl-2-pyridone-5-carboxamide + N-1-methyl-4-pyridone-3-carboxamide)/N-1-methylnicotinamide, was controlled by the activity of N-1-methyl-2-pyridone-5-carboxamide-forming N-1-methylnicotinamide oxidase.