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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). The semiquinone (FADH ·) can be formed by either reduction of FAD or oxidation of FADH 2 by accepting or donating one electron and one proton ...
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 :
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. The double-bonded nitrogen atoms in FAD make it a good acceptor in taking two hydrogen atoms from ...
Two carbon atoms are oxidized to CO 2, the energy from these reactions is transferred to other metabolic processes through GTP (or ATP), and as electrons in NADH and QH 2. The NADH generated in the citric acid cycle may later be oxidized (donate its electrons) to drive ATP synthesis in a type of process called oxidative phosphorylation. [6]
The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system: Equilibrium between the oxidized (left) and totally reduced (right) forms ...
Active site of T. thermophilus hpaB, showing hydrogen bonding of hpaB catalytic residues to 4-hydroxyphenylacetate and to the peroxide bound to FADH 2. (Note: this structure was generated using oxidized FAD in place of FADH 2; the magenta sphere representing oxygen here is actually a water molecule believed to occupy the space oxygen does when the flavin hydroxyperoxide is present.
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 .
The cofactor NADPH binds to the oxidized state of the FAD prosthetic group, reducing it to FADH 2. Molecular oxygen binds to the formed NADP +-FADH 2-enzyme complex and is reduced, resulting in 4a-hydroperoxyflavin (4a-HPF or FADH-OOH).