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FAD can exist in four redox states, which are the flavin-N(5)-oxide, quinone, semiquinone, and hydroquinone. [1] 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 FADH 2 (hydroquinone form).
In enzymology, a FMN adenylyltransferase (EC 2.7.7.2) is an enzyme that catalyzes the chemical reaction ATP + FMN ⇌ {\displaystyle \rightleftharpoons } diphosphate + FAD Thus, the two substrates of this enzyme are ATP and FMN , whereas its two products are diphosphate and FAD .
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.
About 5-10% of flavoproteins have a covalently linked FAD. [2] Based on the available structural data, FAD-binding sites can be divided into more than 200 different types. [3] 90 flavoproteins are encoded in the human genome; about 84% require FAD and around 16% require FMN, whereas 5 proteins require both. [4]
Riboflavin is reversibly converted to FMN and then FAD. From riboflavin to FMN is the function of zinc-requiring riboflavin kinase; the reverse is accomplished by a phosphatase. From FMN to FAD is the function of magnesium-requiring FAD synthase; the reverse is accomplished by a pyrophosphatase. FAD appears to be an inhibitory end-product that ...
Riboflavin is converted into catalytically active cofactors (FAD and FMN) by the actions of riboflavin kinase (EC 2.7.1.26), which converts it into FMN, and FAD synthetase (EC 2.7.7.2), which adenylates FMN to FAD. Eukaryotes usually have two separate enzymes, while most prokaryotes have a single bifunctional protein that can carry out both ...
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Oxidoreductases, enzymes that catalyze oxidation-reduction reactions, constitute Class EC 1 of the IUBMB classification of enzyme-catalyzed reactions. [2] Any of these may be called dehydrogenases, especially those in which NAD + is the electron acceptor (oxidant), but reductase is also used when the physiological emphasis on reduction of the substrate, and oxidase is used only when O 2 is the ...