Flavin adenine dinucleotide

"FAD" redirects here. For other uses, see FAD (disambiguation).

Flavin adenine dinucleotide
Identifiers
CAS number	146-14-5 Y
PubChem	643975
UNII	ZC44YTI8KK Y
EC number	205-663-1
DrugBank	DB03147
KEGG	D00005 N
MeSH	Flavin-Adenine+Dinucleotide
ChEBI	CHEBI:16238 Y
ChEMBL	CHEMBL1232663 N
Beilstein Reference	1208946
Gmelin Reference	108834
3DMet	B04619
Jmol-3D images	Image 1
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
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]
Properties
Molecular formula	C27H33N9O15P2
Molar mass	785.55 g mol−1
Appearance	White, vitreous crystals
log P	-1.336
Acidity (pKa)	1.128
Basicity (pKb)	12.8689
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

In biochemistry, flavin adenine dinucleotide (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. The flavin group is bound to ribitol, a sugar alcohol, by a carbon-nitrogen bond, not a glycosidic bond. Thus, riboflavin is not technically a nucleotide; the name flavin adenine dinucleotide is a misnomer.

FAD can be reduced to FADH₂, whereby it accepts two hydrogen atoms (a net gain of two electrons):

FAD (fully oxidized form, or quinone form) accepts two electrons and two protons to become FADH₂ (hydroquinone form). FADH₂ can then be oxidized to the semireduced form (semiquinone) FADH by donating one electron and one proton. The semiquinone is then oxidized once more by losing an electron and a proton and is returned to the initial quinone form (FAD).

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.

The primary biochemical role of FADH₂ in eukaryotes is to carry high-energy electrons used for oxidative phosphorylation. Its hydrogens remain in the mitochondrial matrix, whilst FAD is tightly bound to a dehydrogenase enzyme i.e. the second protein complex in the oxidative phosphorylation chain. FAD is a prosthetic group in the enzyme complex succinate dehydrogenase (complex II) that oxidizes succinate to fumarate in the eighth step of the citric acid cycle. The high-energy electrons from this oxidation are stored momentarily by reducing FAD to FADH₂. FADH₂ then reverts to FAD, sending its two high-energy electrons through the electron transport chain; the energy in FADH₂ is enough to produce 1.5 equivalents of ATP by oxidative phosphorylation. Another metabolic source of FADH₂ is beta oxidation, where FAD serves as a coenzyme to acyl CoA dehydrogenase.

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

Additional images

• 

  Riboflavin

• 

  FADH2

• 

  Adenine

See also

• Flavin mononucleotide
• NAD
• Thymidylate synthase (FAD), an enzyme that helps produce FAD

External links

• FAD bound to proteins in the PDB