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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).
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 is generally tightly bound (as in adrenodoxin reductase, wherein the FAD is buried deeply). [1] 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]
FAD + 2 H + + 2 e − → FADH 2 (coenzyme bonded to flavoproteins) −0.22 Depending on the protein involved, the potential of the flavine can vary widely [8]
The oxygen binds to FADH − via a single electron transfer, which is the rate-limiting step of the reaction. This forms an FAD radical and flavin hydroperoxide. Reaction between these generates C4a-peroxyflavin, which is quickly protonated to form flavin-C4a-hydroperoxide. [3] Tautomerization leads to the formation of 3,4-dihydoxybenzoate. The ...
FAD, or flavin adenine dinucleotide, is a prosthetic group (a non-polypeptide unit bound to a protein that is required for function) that consists of an adenine nucleotide and a flavin mononucleotide. [10] FAD is a unique electron acceptor. Its fully reduced form is FADH 2 (known as the hydroquinone form), but FAD can also be partially oxidized ...
The flavin product then breaks down with release of water to reform FAD. Due to the low dissociation constant of the NADP +-enzyme complex, [28] NADP + is released by the end of the cycle and the enzyme returns to its original state. The rate-limiting step involves either the breakdown of FADH-OH to water or the release of NADP +. [3] [4]
Mitochondrial glycerol-3-phosphate dehydrogenase (mGPD) then catalyzes the oxidation of G3P by FAD, regenerating DHAP in the cytosol and forming FADH 2 in the mitochondrial matrix. [4] In mammals, its activity in transporting reducing equivalents across the mitochondrial membrane is secondary to the malate–aspartate shuttle.