Flavins refers generally to the class of organic compounds containing the tricyclic heterocycle isoalloxazine or its isomer alloxazine, and derivatives thereof. The biochemical source of flavin 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, 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.
In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as well as cofactor in biological blue-light photo receptors. 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.
Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin. These proteins 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.
4-hydroxyphenylacetate 3-monooxygenase (EC 1.14.14.9) is an enzyme that catalyzes the chemical reaction
In enzymology, an alkanal monooxygenase (FMN-linked) (EC 1.14.14.3) is an enzyme that catalyzes the chemical reaction
In enzymology, an alkanesulfonate monooxygenase (EC 1.14.14.5) is an enzyme that catalyzes the chemical reaction
In enzymology, a Δ7-sterol 5(6)-desaturase is an enzyme that catalyzes the chemical reaction
In enzymology, a cob(II)yrinic acid a,c-diamide reductase is an enzyme that catalyzes the chemical reaction
In enzymology, 6,7-dihydropteridine reductase (EC 1.5.1.34, also Dihydrobiopterin reductase) is an enzyme that catalyzes the chemical reaction
Flavin reductase a class of enzymes. There are a variety of flavin reductases, 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 NAD(P)H dehydrogenase (quinone) (EC 1.6.5.2) is an enzyme that catalyzes the chemical reaction
In enzymology, a NADPH—hemoprotein reductase is an enzyme that catalyzes the chemical reaction
The enzyme chorismate synthase catalyzes the chemical reaction
In enzymology, a riboflavin kinase is an enzyme that catalyzes the chemical reaction
NAD(P)H dehydrogenase, quinone 2, also known as QR2, is a protein that in humans is encoded by the NQO2 gene. It is a phase II detoxification enzyme which can carry out two or four electron reductions of quinones. Its mechanism of reduction is through a ping-pong mechanism involving its FAD cofactor. Initially in a reductive phase NQO2 binds to reduced dihydronicotinamide riboside (NRH) electron donor, and mediates a hydride transfer from NRH to FAD. Then, in an oxidative phase, NQO2 binds to its quinone substrate and reduces the quinone to a dihydroquinone. Besides the two catalytic FAD, NQO2 also has two zinc ions. It is not clear whether the metal has a catalytic role. NQO2 is a paralog of NQO1
NQO2 is a homodimer. NQO2 can be inhibited by resveratrol. One of QR2's binding sites responds to 2-iodomelatonin, and has been referred to as MT3.
FMN reductase (NADPH) (EC 1.5.1.38, FRP, flavin reductase P, SsuE) is an enzyme with systematic name FMNH2:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction:
FMN reductase (NAD(P)H) (EC 1.5.1.39, FRG) is an enzyme with systematic name FMNH2:NAD(P)+ oxidoreductase. This enzyme catalyses the following chemical reaction
Riboflavin reductase (NAD(P)H) (EC 1.5.1.41, NAD(P)H-FMN reductase, Fre) is an enzyme with systematic name riboflavin:NAD(P)+ oxidoreductase. This enzyme catalyses the following chemical reaction
FMN reductase (NADH) (EC 1.5.1.42, NADH-FMN reductase) is an enzyme with systematic name FMNH2:NAD+ oxidoreductase. This enzyme catalyses the following chemical reaction
