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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).
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:
90 flavoproteins are encoded in the human genome; about 84% require FAD and around 16% require FMN, whereas 5 proteins require both. [4] Flavoproteins are mainly located in the mitochondria . [ 4 ] Of all flavoproteins, 90% perform redox reactions and the other 10% are transferases , lyases , isomerases , ligases .
Many contain the nucleotide adenosine monophosphate (AMP) as part of their structures, such as ATP, coenzyme A, FAD, and NAD +. This common structure may reflect a common evolutionary origin as part of ribozymes in an ancient RNA world. It has been suggested that the AMP part of the molecule can be considered to be a kind of "handle" by which ...
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 as FADH by either reducing FAD or oxidizing FADH 2. [11] Dehydrogenases typically fully reduce FAD to FADH 2. The production of FADH is rare.
FAD is the hydrogen acceptor, yielding FADH2. [7] 2. Enoyl-CoA hydrase catalyzes the addition of water across the newly formed double bond to make an alcohol. [5] [6] 3. 3-hydroxyacyl-CoA dehydrogenase oxidizes the alcohol group to a ketone. [5] NADH is produced from NAD+. [6] 4.
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 E 3 component is a flavoprotein, and it re-oxidizes the reduced lipoyl sulfur residues of E 2 using FAD (a catalytic cofactor) as the oxidant. FAD then transfers these protons and electrons to NAD+ (a stoichiometric cofactor) to complete the reaction cycle.