Abstract
Pyridazine-3-carboxylic acid (Pyd-3-CA), which is an analogue of nicotinic acid (NiA), inhibits competitively the growth of Lactobacillus arabinosus 17-5,and the inhibition index exhibits about 2200. On the other hand, it inhibits noncompetitively the growth of Escherichia coli B, which is able to synthesize NiA by itself. The later inhibition is, however, recovered only by NiA or nicotinamide (NAA), and is similar to the action of 6-aminonicotinamide (ANAA) known as the most potent antagonist of NAA. Pyd-3-CA is slightly less potent than ANAA for E. coli B, but it is interesting that, while the inhibition by ANAA is more effectively recovered by NAA than NiA, in the case of Pyd-3-CA the recovery of the inhibition by NiA is rather more than by NAA.
