N1-Methylnicotinamide Oxidation in a Number of Mammals

Mammalian livers contain an enzyme system which can oxidize N1-methylnicotinamide to N1-methyl-4-pyridone-3-carboxamide (4-pyridone) and N1-methyl-2-pyridone-5-carboxamide (2-pyridone). Many of the properties of this enzyme system are similar to those which have been reported for rabbit liver aldehyde oxidase. Both pyridones are made in all the mammals examined, although in varying ratios. The ratio of the 2-pyridone to the 4-pyridone is constant for a a given species. The ratio characteristic of the oxidation of N1-methylnicotinamide by the enzyme system in the livers of mice and hogs is maintained under a variety of conditions including purification, heat denaturation, variation in type and amount of oxygen accepter, variation in substrate concentration, inhibition by cyanide, and loss of activity due to storage at -15°. These data have been taken as preliminary evidence in support of the concept that the two pyridones are synthesized from N1-methylnicotinamide by a single enzyme. The differential effects on the synthesis of the two pyridones exerted by Amytal and variation in the pH of the assay media have been observed. These findings may be indicative of different binding states or catalytic requirements for the two different oxidation processes or both. The gross similarities in the hog, mouse, and rabbit activities are compatible with all being attributable to aldehyde oxidases having similar but not identical structures.