Enzymes that control the conversion of L-tryptophan-nicotinamide and the urinary excretion ratio (N1-methyl-2-pyridone-5-carboxamide + N 1-methyl-4-pyridone-3-carboxamide)/N1-methylnicotinamide in mice

Abstract

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 (N1-methyl-2-pyridone-5-carboxamide + N1-methyl- 4-pyridone-3-carboxamide)/N1-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%) < 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 (N1-methyl- 2-pyridone-5-carboxamide + N 1-methyl-4-pyridone-3- carboxamide)/N1-methylnicotinamide, was controlled by the activity of N1-methyl-2-pyridone-5- carboxamide- forming N1-methylnicotinamide oxidase.