FADH2

Flavin adenine dinucleotide

Identifiers
CAS Number	146-14-5 Y
3D model (Jmol)	Interactive image
3DMet	B04619
Beilstein Reference	1208946
ChEBI	CHEBI:16238 Y
ChEMBL	ChEMBL1232653 N
DrugBank	DB03147 Y
ECHA InfoCard	100.005.149
EC Number	205-663-1
Gmelin Reference	108834
IUPHAR/BPS	5184
KEGG	D00005 N
MeSH	Flavin-Adenine+Dinucleotide
PubChem	643975
UNII	ZC44YTI8KK Y
InChI InChI=1S/C27H33N9O15P2/c1-10-3-12-13(4-11(10)2)35(24-18(32-12)25(42)34-27(43)33-24)5-14(37)19(39)15(38)6-48-52(44,45)51-53(46,47)49-7-16-20(40)21(41)26(50-16)36-9-31-17-22(28)29-8-30-23(17)36/h3-4,8-9,14-16,19-21,26,37-41H,5-7H2,1-2H3,(H,44,45)(H,46,47)(H2,28,29,30)(H,34,42,43)/t14-,15+,16+,19-,20+,21+,26+/m0/s1 Y[PubChem] Key: VWWQXMAJTJZDQX-UYBVJOGSSA-N Y[PubChem]
SMILES CC1=CC2=C(C=C1C)N(C3=NC(=O)NC(=O)C3=N2)C[C@@H]([C@@H]([C@@H](COP(=O)(O)OP(=O)(O)OC[C@@H]4[C@H]([C@H]([C@@H](O4)N5C=NC6=C5N=CN=C6N)O)O)O)O)O
Properties
Chemical formula	C27H33N9O15P2
Molar mass	785.56 g·mol−1
Appearance	White, vitreous crystals
log P	-1.336
Acidity (pKa)	1.128
Basicity (pKb)	12.8689
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

In biochemistry, flavin adenine dinucleotide (FAD) is a redox cofactor, more specifically a prosthetic group, involved in several important reactions in metabolism. FAD can exist in three (or four: flavin-N(5)-oxide) different redox states, which are the quinone, semiquinone, and hydroquinone. FAD is converted between these states by accepting or donating electrons.

FAD, in its fully oxidized form, or quinone form, accepts two electrons and two protons to become FADH₂ (hydroquinone form). The semiquinone (FADH^·) can be formed by either reduction of FAD or oxidation of FADH₂ by accepting or donating one electron and one proton, respectively. See the mechanism section below for details.

A flavoprotein is a protein that contains a flavin moiety, this may be in the form of FAD or flavin mononucleotide (FMN). There are many flavoproteins besides components of the succinate dehydrogenase complex, including α-ketoglutarate dehydrogenase and a component of the pyruvate dehydrogenase complex, some examples are shown in section 6.

Flavoproteins were first discovered in 1879 by separating components of cow’s milk. They were initially called lactochrome due to their milky origin and yellow pigment. It took 50 years for the scientific community to make any substantial progress in identifying the molecules responsible for the yellow pigment. The 1930s launched the field of coenzyme research with the publication of many flavin and nicotinamide derivative structures and their obligate roles in redox catalysis. German scientists Warburg and Christian discovered a yeast derived yellow protein required for cellular respiration in 1932. Their colleague Hugo Theorell separated this yellow enzyme into apoenzyme and yellow pigment and showed that neither the enzyme alone or the pigment was capable of oxidizing NADH on their own but mixing them together would restore activity. Theorell confirmed the pigment to be riboflavins phosphate ester, flavin mononucleotide (FMN) in 1937, which was the first direct evidence for enzyme cofactors. Warburg and Christian then found FAD to be a cofactor of D-amino acid oxidase through similar experiments in 1938.Otto Warburg’s work with linking nicotinamide to hydride transfers and the discovery of flavins paved the way for many scientists in the 40s and 50s to discover copious amounts of redox biochemistry and link them together in pathways such as the citric acid cycle and ATP synthesis.