Flavin mononucleotide

Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as prosthetic group of various oxidoreductases including NADH dehydrogenase as well as cofactor in biological blue-light photo receptors.[1] During the catalytic cycle, a reversible interconversion of the oxidized (FMN), semiquinone (FMNH) and reduced (FMNH2) forms occurs in the various oxidoreductases. FMN is a stronger oxidizing agent than NAD and is particularly useful because it can take part in both one- and two-electron transfers. In its role as blue-light photo receptor, (oxidized) FMN stands out from the 'conventional' photo receptors as the signaling state and not an E/Z isomerization.

It is the principal form in which riboflavin is found in cells and tissues. It requires more energy to produce, but is more soluble than riboflavin.

Flavin mononucleotide
Skeletal formula of flavin mononucleotide
Ball-and-stick model of the flavin mononucleotide molecule
Other names
3D model (JSmol)
ECHA InfoCard 100.005.150
E number E101a (colours)
MeSH Flavin+mononucleotide
Molar mass 456.344 g/mol
Melting point 195 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Food additive

Flavin mononucleotide is also used as an orange-red food colour additive, designated in Europe as E number E101a.[2]

E106, a very closely related food dye, is riboflavin-5′-phosphate sodium salt, which consists mainly of the monosodium salt of the 5′-monophosphate ester of riboflavin. It is rapidly turned to free riboflavin after ingestion. It is found in many foods for babies and young children as well as jams, milk products, and sweets and sugar products.

See also


  1. ^ Tsibris, John C. M.; McCormick, Donald B.; Wright, Lemuel D. "Studies on the Binding and Function of Flavin Phosphates with Flavin Mononucleotide-dependent Enzymes". Journal of Biological Chemistry.
  2. ^ "Current EU approved additives and their E Numbers", Food Standards Agency website, retrieved 15 Dec 2011

External links

12-oxophytodienoate reductase

12-oxophytodienoate reductase (OPRs) is an enzyme of the family of Old Yellow Enzymes (OYE). OPRs are grouped into two groups: OPRI and OPRII – the second group is the focus of this article, as the function of the first group is unknown, but is the subject of current research. The OPR enzyme utilizes the cofactor flavin mononucleotide (FMN) and catalyzes the following reaction in the jasmonic acid synthesis pathway:

This reaction occurs in peroxisomes in plants. Several isozymes have been discovered, with varying substrate stereospecificity: three in Lycopersicon esculentum, 13 in Oryza sativa, and five in Arabidopsis thaliana. The OPR3 isozyme is most extensively studied because it can reduce all 4 stereoisomers of the substrate, OPDA and because it has shown to be the most significant enzyme in the jasmonic acid synthesis pathway.

Chorismate synthase

In enzymology, a chorismate synthase (EC is an enzyme that catalyzes the chemical reaction

5-O-(1-carboxyvinyl)-3-phosphoshikimate chorismate + phosphate

Hence, this enzyme has one substrate, 5-O-(1-carboxyvinyl)-3-phosphoshikimate, and two products, chorismate and phosphate.

This enzyme belongs to the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. The systematic name of this enzyme class is 5-O-(1-carboxyvinyl)-3-phosphoshikimate phosphate-lyase (chorismate-forming). This enzyme is also called 5-O-(1-carboxyvinyl)-3-phosphoshikimate phosphate-lyase. This enzyme participates in phenylalanine, tyrosine and tryptophan biosynthesis.

Chorismate synthase catalyzes the last of the seven steps in the shikimate pathway which is used in prokaryotes, fungi and plants for the biosynthesis of aromatic amino acids. It catalyzes the 1,4-trans elimination of the phosphate group from 5-enolpyruvylshikimate-3-phosphate (EPSP) to form chorismate which can then be used in phenylalanine, tyrosine or tryptophan biosynthesis. Chorismate synthase requires the presence of a reduced flavin mononucleotide (FMNH2 or FADH2) for its activity. Chorismate synthase from various sources shows a high degree of sequence conservation. It is a protein of about 360 to 400 amino-acid residues.


Deiodinase (or iodide peroxidase or "Monodeiodinase") is a peroxidase enzyme that is involved in the activation or deactivation of thyroid hormones.


5,6-Dimethylbenzimidazole is a natural benzimidazole derivative. It is a component of vitamin B12 where is serves as a ligand for the cobalt atom.5,6-Dimethylbenzimidazole is biosynthesized from flavin mononucleotide by the enzyme 5,6-dimethylbenzimidazole synthase.


E101 may refer to:

Riboflavin, food additive which has been assigned E number 101

Flavin mononucleotide, biomolecule produced from riboflavin

European route E101, autoroad of International E-road network between Kiev and Moscow

E101, a form for stating applicable legislation within the European Economic Area and Switzerland


FMN may refer to:

Federated Mission Networking

Facial motor nucleus

Flavin mononucleotide

Flour Mills of Nigeria, a Nigerian agribusiness company

FMN (TV channel), Indonesia


Four Corners Regional Airport outside Farmington, New Mexico, United States

Ministry of Defence (Denmark) (Danish: Forsvarsministeriet)

Narrowband FM, or frequency modulation narrow

FMN-binding fluorescent protein

A FMN-binding fluorescent protein (FbFP or LOV-based fluorescent protein) is a small, oxygen-independent fluorescent protein that binds flavin mononucleotide (FMN) as a chromophore.

They were developed from blue-light receptors (so called LOV-domains) found in plants and various bacteria. They complement the GFP-derivatives and –homologues and are particularly characterized by their independence of molecular oxygen and their small size. FbFPs absorb blue light and emit light in the cyan-green spectral range.

FMN reductase

In enzymology, an FMN reductase (EC is an enzyme that catalyzes the chemical reaction

FMNH2 + NAD(P)+ FMN + NAD(P)H + H+

The 3 substrates of this enzyme are FMNH2, NAD+, and NADP+, whereas its 4 products are FMN, NADH, NADPH, and H+.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is FMNH2:NAD(P)+ oxidoreductase. Other names in common use include NAD(P)H-FMN reductase, NAD(P)H-dependent FMN reductase, NAD(P)H:FMN oxidoreductase, NAD(P)H:flavin oxidoreductase, NAD(P)H2 dehydrogenase (FMN), NAD(P)H2:FMN oxidoreductase, SsuE, riboflavin mononucleotide reductase, flavine mononucleotide reductase, riboflavin mononucleotide (reduced nicotinamide adenine dinucleotide, (phosphate)) reductase, flavin mononucleotide reductase, and riboflavine mononucleotide reductase.

FMN riboswitch

The FMN riboswitch (also known as RFN element) is a highly conserved RNA element that is found frequently in the 5'-untranslated regions of prokaryotic mRNAs that encode for flavin mononucleotide (FMN) biosynthesis and transport proteins. This element is a metabolite-dependent riboswitch that directly binds FMN in the absence of proteins. In Bacillus subtilis, the riboswitch controls gene expression by causing premature transcription termination within the 5' untranslated region of the ribDEAHT operon and precluding access to the ribosome-binding site of ypaA mRNA.

Flavin adenine dinucleotide

In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several important enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, 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.

FAD can exist in four different redox states, which are the flavin-N(5)-oxide, 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. Some proteins, however, generate and maintain a superoxidized form of the flavin cofactor, the flavin-N(5)-oxide.

Flavin group

Flavin (from Latin flavus, "yellow") is the common name for a group of organic compounds based on pteridine, formed by the tricyclic heterocycle isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and, in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic group in flavoproteins.

The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system:

In aqueous solution, flavins are yellow-coloured when oxidized, taking a red colour in the semi-reduced anionic state or blue in the neutral (semiquinone) state, and colourless when totally reduced. The oxidized and reduced forms are in fast equilibrium with the semiquinone (radical) form, shifted against the formation of the radical:

Flox + FlredH2 ⇌ FlH•where Flox is the oxidized flavin, FlredH2 the reduced flavin (upon addition of two hydrogen atoms) and FlH• the semiquinone form (addition of one hydrogen atom).

In the form of FADH2, it is one of the cofactors that can transfer electrons to the electron transfer chain.

Flavin reductase

Flavin reductase is in a class of enzymes which catalyzes the reduction of a substrate. There are a variety of flavin reductases, (i.e. FRP, FRE, FRG, etc.) which bind free flavins and through hydrogen bonding, catalyze the reduction of these molecules to a reduced flavin. Riboflavin, or vitamin B, and flavin mononucleotide are two of the most well known flavins in the body and are used in a variety of processes which include metabolism of fat and ketones and the reduction of methemoglobin in erythrocytes. Flavin reductases are similar and often confused for ferric reductases because of their similar catalytic mechanism and structures.

In enzymology, a flavin reductase (EC is an enzyme that catalyzes the chemical reaction

riboflavin + NADPH + H+ reduced riboflavin + NADP + H+

Thus, the two products of this enzyme are reduced riboflavin and NADP+, whereas its 3 substrates are riboflavin, NADPH, and H+.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is reduced-riboflavin:NADP+ oxidoreductase. Other names in common use include NADPH:flavin oxidoreductase, riboflavin mononucleotide (reduced nicotinamide adenine dinucleotide, phosphate) reductase, flavin mononucleotide reductase, flavine mononucleotide reductase, FMN reductase (NADPH), NADPH-dependent FMN reductase, NADPH-flavin reductase, NADPH-FMN reductase, NADPH-specific FMN reductase, riboflavin mononucleotide reductase, riboflavine mononucleotide reductase, NADPH2 dehydrogenase (flavin), and NADPH2:riboflavin oxidoreductase.


Flavodoxins are electron-transfer proteins. Flavodoxin is a bacterial protein that includes flavin mononucleotide. The structure of flavodoxin is characterized by a five-stranded parallel beta sheet, surrounded by alpha helices at either side of the sheet. They have been isolated from prokaryotes, cyanobacteria, and some eukaryotic algae.


Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN).

Flavoproteins are involved in a wide array of biological processes, including removal of radicals contributing to oxidative stress, photosynthesis, and DNA repair. The flavoproteins are some of the most-studied families of enzymes.

Flavoproteins have either FMN or FAD as a prosthetic group or as a cofactor. The flavin is generally tightly bound (see example adrenodoxin reductase wherein the FAD is deeply buried in the enzyme).

About 5-10% of flavoproteins have a covalently linked FAD. Based on the available structural data, FAD-binding sites can be divided into more than 200 different types.90 flavoproteins are encoded in the human genome; about 84% require FAD, and around 16% require FMN, whereas 5 proteins require both. Flavoproteins are mainly located in the mitochondria. Of all flavoproteins, 90% perform redox reactions and the other 10% are transferases, lyases, isomerases, ligases.

Nitric oxide synthase

Nitric oxide synthases (EC (NOSs) are a family of enzymes catalyzing the production of nitric oxide (NO) from L-arginine. NO is an important cellular signaling molecule. It helps modulate vascular tone, insulin secretion, airway tone, and peristalsis, and is involved in angiogenesis and neural development. It may function as a retrograde neurotransmitter. Nitric oxide is mediated in mammals by the calcium-calmodulin controlled isoenzymes eNOS (endothelial NOS) and nNOS (neuronal NOS). The inducible isoform, iNOS, involved in immune response, binds calmodulin at physiologically relevant concentrations, and produces NO as an immune defense mechanism, as NO is a free radical with an unpaired electron. It is the proximate cause of septic shock and may function in autoimmune disease.

NOS catalyzes the reaction:

NOS isoforms catalyze other leak and side reactions, such as superoxide production at the expense of NADPH. As such, this stoichiometry is not generally observed, and reflects the three electrons supplied per NO by NADPH.

NOSs are unusual in that they require five cofactors. Eukaryotic NOS isozymes are catalytically self-sufficient. The electron flow in the NO synthase reaction is: NADPH → FAD → FMN → heme → O2. Tetrahydrobiopterin provides an additional electron during the catalytic cycle which is replaced during turnover. NOS is the only known enzyme that binds flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), heme, tetrahydrobiopterin (BH4) and calmodulin.[citation needed]


Ribitol, or adonitol, is a crystalline pentose alcohol (C5H12O5) formed by the reduction of ribose. It occurs naturally in the plant Adonis vernalis as well as in the cell walls of some Gram-positive bacteria, in the form of ribitol phosphate, in teichoic acids. It also forms part of the chemical structure of riboflavin and flavin mononucleotide (FMN), which is a nucleotide coenzyme used by many enzymes, the so-called flavoproteins.

Riboflavin carrier protein

Riboflavin carrier proteins (RFCPs) together with human serum albumin transport flavin mononucleotide (FMN) in the blood circuit. RFCPs are important in pregnancy.

Studies from India have identified a riboflavin carrier protein (RCP) present in bird (e.g., chicken) eggs, which is considered to be specific for riboflavin, and is essential for normal embryological development. If this protein is rendered ineffective (e.g., by immuno-neutralization) by treatment of the bird with a specific antibody, then embryonic development ceases and the embryo dies. A genetic mutant lacking RCP is likewise infertile. A homologous protein, which can be rendered ineffective by the antibody to pure chicken riboflavin carrier protein, has been shown to occur in several mammalian species, including two species of monkeys, and also in humans. Very recent studies have suggested that circulating RCP levels and the immunohistochemical staining of RCP in biopsy specimens may provide new markers for breast cancer diagnosis and prognosis. Termination of pregnancy has been demonstrated by immuno-neutralization of RCP in monkeys. There remains some controversy over the roles of RCP, however, the other, less specific riboflavin binders in blood, including gamma-gobulins, also seem to play an important role. These studies have provided an intriguing example of the role of specific vitamin-transporting mechanisms, designed to ensure that the vitamin needs of the developing embryo will be efficiency met. Further evidence of the special needs of developing embryos has been provided by the demonstration that riboflavin analogs can cause teratogenic changes, even in the absence of any detectable damage to maternal tissues.

Riboflavin reductase (NAD(P)H)

Riboflavin reductase (NAD(P)H) (EC, NAD(P)H-FMN reductase, Fre) is an enzyme with systematic name riboflavin:NAD(P)+ oxidoreductase. This enzyme catalyses the following chemical reaction

reduced riboflavin + NAD(P)+ riboflavin + NAD(P)H + H+

This enzyme catalyses the reduction of soluble flavins.

The structure of the protein suggests that the enzymatic mechanism of flavin reductase is of a bisubstrate-biproduct nature3. Due to its structural features, the enzyme is not able to bind both NAD(P)H and flavin at the same time. Therefore, in the proposed mechanism the flavin reductase first binds NAD(P)H and stabilizes the release of a hydride3. Next, NAD(P)+ is released and the flavin mononucleotide binds to the enzyme. This is followed by further protonation when the hydride attacks a nitrogen atom on the flavin mononucleotide3. Finally, the reduced flavin is released from flavin reductase. If this mechanism is indeed correct, it suggests that the reduction of flavin by flavin reductase is dependent on the enzyme binding first to NAD(P)H3.

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