Flavin Adenine Dinucleotide (FAD)

In biochemistry, FAD) is a redox cofactor involved in several important reactions in metabolism. FAD can exist in two different redox states, which it converts between by accepting or donating electrons. The molecule consists of a riboflavin moiety (vitamin B₂) bound to the phosphate group of an ADP molecule. Note that the flavin group is bound to ribitol (sugar alcohol) by a carbon-nitrogen bond, not a glycosidic bond; riboflavin is thus not technically a nucleotide and the name flavin adenine dinucleotide is a misnomer. FAD is an aromatic ring system, whereas FADH₂ is not. This means that FADH₂ is significantly higher in energy, without the stabilization that aromatic structure provides. FADH₂ is an energy carrying molecule, because if it is oxidized, it will regain aromaticity and release all the energy represented by this stabilization.