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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 ...
Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B 2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as well as a cofactor in biological blue-light photo receptors. [1]
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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 ...