has role is protonated form of nicotinic acid A pyridinemonocarboxylic acid that is pyridine in which the hydrogen at position 3 is replaced by a carboxy group. vitamin B3 pyridine alkaloid pyridinemonocarboxylic acid nicotinate vasodilator agent antilipemic drug antidote mouse metabolite plant metabolite Escherichia coli metabolite human urinary metabolite EC 3.5.1.19 (nicotinamidase) inhibitor