(niacin) A carboxylic acid, formula C5
NCOOH, so named because it forms part of the alkaloid nicotine. It is a member of the Β group of *vitamins
and is formed in plants and most animals (but not man) from various precursors, notably tryptophan. In the form of the amide nicotinamide, C5
, it is a constituent of the coenzymes NAD and NADP. Certain plant products, notably maize, are very poor in nicotinic acid. If these form the basis of a human diet, pellagra, caused by nicotinic acid deficiency, results.