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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).
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]
Structure of the medium-chain acyl-CoA dehydrogenase tetramer. FAD molecules are shown in yellow. The medium chain acyl-CoA dehydrogenase (MCAD) is the best known structure of all ACADs, and is the most commonly deficient enzyme within the class that leads to metabolic disorders in animals. [1]
The Rossmann fold is a tertiary fold found in proteins that bind nucleotides, such as enzyme cofactors FAD, NAD +, and NADP +.This fold is composed of alternating beta strands and alpha helical segments where the beta strands are hydrogen bonded to each other forming an extended beta sheet and the alpha helices surround both faces of the sheet to produce a three-layered sandwich.
In order to work as a catalyst, GOx requires a coenzyme, flavin adenine dinucleotide (FAD). FAD is a common component in biological oxidation-reduction reactions. Redox reactions involve a gain or loss of electrons from a molecule. In the GOx-catalyzed redox reaction, FAD works as the initial electron acceptor and is reduced to FADH −. [12]
Together, the alpha and beta units are arranged in an α 6 β 6 structure. [3] [4] The catalytic activities of this enzyme complex involves a coordination system of enzymatic reactions between the alpha and beta subunits. The enzyme complex therefore consists of six functional centers for fatty acid synthesis. [3] [5]
2,4 Dienoyl-CoA Reductase from Escherichia coli shares very similar kinetic properties to that of eukaryotes, but differs significantly in both structure and mechanism. In addition to NADPH, E. Coli DECR requires a set of FAD, FMN and iron–sulfur cluster molecules to complete the electron transfer. [12]
The glutamate residue is highly conserved because it both stabilizes the semiquinone form of FAD and is a proton donor/acceptor in the reaction. [5] The rate limiting step of the electron transfer reaction is the release of the first oxidized ferredoxin molecule after the reduction of FAD with one electron. [3]