Translations:Niacin/49/en
Niacin and nicotinamide are both converted into the coenzyme NAD. NAD converts to NADP by phosphorylation in the presence of the enzyme NAD+ kinase. High energy requirements (brain) or high turnover rate (gut, skin) organs are usually the most susceptible to their deficiency. In the liver, niacinamide is converted to storage nicotinamide adenine dinucleotide (NAD). As needed, liver NAD is hydrolyzed to niacinamide and niacin for transport to tissues, there reconverted to NAD to serve as an enzyme cofactor. Excess niacin is methylated in the liver to N1-methylnicotinamide (NMN) and excreted in urine as such or as the oxidized metabolite N1-methyl-2-pyridone-5-carboxamide (2-pyridone). Decreased urinary content of these metabolites is a measure of niacin deficiency.
