Enzymes that control the conversion of L-tryptophan-nicotinamide and the urinary excretion ratio (N(1)-methyl-2-pyridone-5-carboxamide + N(1)-methyl-4-pyridone-3-carboxamide)/N(1)-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.