Studies of Antimetabolites* Ii. I-acetylpyridine

When 3acetylpyridine (3-AP) is fed to dogs, large amounts of a normal end-product of nicotinic acid metabolism, N’-methylnicotinamide (NMeN), appear in the urine (1). This finding might be interpreted as evidence that 3-AP, acting as an antivitamin, displaces nicotinamide from its nucleotides or prevents its incorporation therein, or, alternatively, that 3-AP is biologically oxidized to nicotinic acid and is thus, in a sense, a provitamin. In the present study, these conjectures have been tested by feeding 3-AP containing an excess of Cl3 in the carbonyl group. If NMeN excreted after ingestion of tagged 3-AP arises only from displaced nicotinamide or unutilized nicotinic acid formed from tryptophan, it should not contain an excess of C3, while if it is derived from nicotinic acid arising by direct oxidation of tagged 3-AP, it should contain a large excess of the isotope.