Noun
a coenzyme present in most living cells and derived from the B vitamin nicotinic acid; serves as a reductant in various metabolic processes
Source: WordNetDuring the metabolism of alcohol via the respective dehydrogenases, NAD ( Nicotinamide adenine dinucleotide ) is converted into reduced NAD. Source: Internet
This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to reduce their substrates. citation Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. Source: Internet