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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, 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 ...
It uses FAD as an electron acceptor and it is reduced to FADH 2. Trans-delta 2-enoyl CoA is hydrated at the double bond to produce L-3-hydroxyacyl CoA by enoyl-CoA hydratase. L-3-hydroxyacyl CoA is dehydrogenated again to create 3-ketoacyl CoA by 3-hydroxyacyl CoA dehydrogenase. This enzyme uses NAD as an electron acceptor.
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.
Flavin adenine dinucleotide (FAD) is a required co-factor in addition to the presence of an active site glutamate in order for the enzyme to function. The following reaction is the oxidation of the fatty acid by FAD to afford an α,β-unsaturated fatty acid thioester of coenzyme A:
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 ...