Abstract
The catabolism of nicotinamide in riboflavin-deficient rats was compared with that in control rats. In riboflavin-deficient rats, no activities of N^1-methyl-2-pyridone-5-carboxamide (2-Pyr)-forming N^1-methylnicotinamide (MNA) oxidase and N^1-metyl-4-pyridone-3-carboxamide (4-Pyr)-forming MNA oxidase were not detected in vitro, however, the nicotinamide methyltransferase activity was not changed compared with the control rats. As a result, the excretion of MNA was higher in riboflavin-deficient rats than in control rats and the excretion of 2-Pyr and 4-Pyr was lower in riboflavin-deficient rats than in the control rats. Therefore, the resulting excretion ratio of (2-Pyr +4-Pyr )/MNA was greatly lower in the riboflavin-deficient rats than in the control rats.
