1,4-Dihydronicotinamide adenine dinucleotide
NADH is the reduced form of NAD+, and NAD+ is the oxidized form of NADH, a coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). It forms NADP with the addition of a phosphate group to the 2' position of the adenosyl nucleotide through an ester linkage. (Dorland, 27th ed)