Flavin adenine dinucleotide

Definition

noun
plural: flavin adenine dinucleotides
fla·vin ad·e·nine di·nu·cle·o·tide, ad·e·nine daɪˈnjuːklɪəˌtaɪd
A biomolecule (chemical formula: C₂₇H₃₃N₉O₁₅P₂) derived from riboflavin (vitamin B2), and functions in various metabolic activities such as acting as a redox cofactor in various oxidation-reduction reactions

Details

Overview

Flavin adenine dinucleotide (FAD) is a dinucleotide, which means that it is a type of nucleotide distinguished by being comprised of two monomers. Each monomer, in turn, is made up of a nucleobase, a pentose, and phosphate group.

Characteristics

Flavin adenine dinucleotide (FAD) (chemical formula: C₂₇H₃₃N₉O₁₅P₂) is a dinucleotide also referred to as riboflavin 5′-adenosine diphosphate. It is a biomolecule with riboflavin at its core. Thus, the flavin in its name denotes to where it is derived from, i.e. riboflavin (also known as vitamin B2. Etymologically, flavin is derived from the Latin term flavus, for “yellow”. That is because riboflavin comes from ribose and flavin, which is the ring-moiety that imparts the yellow color to the oxidized molecule. Thus, FAD belongs to a group of flavins, which refer to organic compounds formed by the tricyclic heterocycle isoalloxazine. Another example of flavin compound is flavin mononucleotide (FMN), which is a biomolecule (chemical formula: C₁₇H₂₁N₄O₉P) that also serves as a cofactor in various oxidation-reduction reactions.
There are two main portions of FAD: (1) adenine and (2) flavin mononucleotide. The two portions are joined together at their phosphate groups. FAD occurs in different redox states: quinone, semiquinone, and hydroquinone. It converts from one state to another either by accepting or donating electrons. Quinone is the fully oxidized form of FAD. When it accepts two electrons (e^–) and two protons (H⁺) it converts to the hydroquinone form, FADH₂. FADH₂ can convert to FADH when it losses one H⁺ and one e^–, and losing another H⁺ and one e^– reverts it to FAD. FAD can be produced by the reduction and dehydration of flavin-N(5)-oxide.¹

Common biological reactions

Common biological reactions

Bacteria, fungi, and plants are capable of biosynthesizing riboflavin. Other eukaryotes need such organisms to obtain riboflavin. Thus, humans can derive riboflavin from dietary sources. Riboflavin-containing food is digested to release riboflavin to be taken up by the small intestine. It is then transported to cells through carrier proteins. Through the action of the enzyme riboflavin kinase, FMN is produced by the addition of a phosphate group to riboflavin. FMN may then be converted into FAD through the action of (1) the enzyme FAD synthetase that adds adenine nucleotide to FMN and (2) ATP.

Common biological reactions

FAD (as well as FMN) acts as an oxidizing agent. Both FAD and FMN can accept either one electron in a two-step process or two electrons at once.² One of the most crucial reactions FAD is involved with is in the citric acid cycle. Succinate dehydrogenase is an enzyme that oxidizes succinate to be converted into fumarate by coupling it with the reduction of ubiquinone to ubiquinol. The electrons from the oxidation are stored transiently by the reduction of FAD to FADH₂. FADH₂ reverts to FAD by sending two electrons through the electron transport chain.

Biological importance/functions

FAD is a dinucleotide that acts as a cofactor in redox reactions. FAD, just as FMN, forms certain flavoproteins when conjugated with certain proteins. Flavoproteins are proteins containing a flavin moiety. These proteins are essential in many biological processes, such as DNA repair, bioluminescence, photosynthesis, and the removal of free radicals.

Supplementary

Abbreviation(s)

• FAD

Variant

• Flavine adenine dinucleotide

IUPAC name

• ({(2R,3S,4R,5R)-5-(6-amino-9H-purin-9-yl)-3,4-dihydroxyoxolan-2-ylmethoxy}(hydroxy)phosphoryl)oxy({(2R,3S,4S)-5-{7,8-dimethyl-2,4-dioxo-2H,3H,4H,10H-benzogpteridin-10-yl}-2,3,4-trihydroxypentyloxy})phosphinic acid

Chemical formula

• C₂₇H₃₃N₉O₁₅P₂

Synonyms

• Adenine-flavin dinucleotide
• Adenine-riboflavine dinucleotide
• Adeflavin
• Riboflavin 5′-adenosine diphosphate

Further reading

See also

• nucleotide
• flavin mononucleotide (FMN)
• flavoprotein
• Fad pyrophosphatase
• Riboflavin
• coenzyme
• cofactor

Reference

1. Devlin, edited by Thomas M. (2011). Textbook of biochemistry: with clinical correlations (7th ed.). Hoboken, NJ: John Wiley & Sons.
2. Wikipedia Contributors. (2019, March 14). Flavin group. Retrieved from Wikipedia website: https://en.wikipedia.org/wiki/Flavin_group

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