FADH2, Flavin adenine dinucleotide reduced

FADH2 flavin adenine dinucleotide (reduced form)... 

FAD flavin adenine dinucleotide (oxidized form) FADH2 flavin adenine dinucleotide (reduced form) fMet formylmethionine FMN flavin mononucleotide (oxidized form) FMNH2 flavin mononucleotide (reduced form)... 

FIGURE 2 Some important reactions in metabolism. Shown are the phosphorylation of ADP to ATP, NAD+, NADH, FAD, FADH2 acetate, CoA, and acetyl CoA. For clarity, just the parts of the larger molecules that undergo reaction are shown. NAD+, nicotinamide adenine dinucleotide NADH, nicotinamide adenine dinucleotide (reduced form) FAD, flavin adenine dinucleotide FADH2, flavin adenine dinucleotide (reduced form) CoA, coenzyme A AMP, adenosine monophosphate. 

This thiol-disulfide interconversion is a key part of numerous biological processes. WeTJ see in Chapter 26, for instance, that disulfide formation is involved in defining the structure and three-dimensional conformations of proteins, where disulfide "bridges" often form cross-links between q steine amino acid units in the protein chains. Disulfide formation is also involved in the process by which cells protect themselves from oxidative degradation. A cellular component called glutathione removes potentially harmful oxidants and is itself oxidized to glutathione disulfide in the process. Reduction back to the thiol requires the coenzyme flavin adenine dinucleotide (reduced), abbreviated FADH2. 

Fig. 1. Energy metabolism in the normal myocardium (ATP adenosine-5 -triphosphate, ADP adenosine-5 -diphosphate, P phosphate, PDH pyruvate dehydrogenase complex, acetyl-CoA acetyl-coenzyme A, NADH and NAD" nicotinamide adenine dinucleotide (reduced and oxidized), FADH2 and FAD flavin adenine dinucleotide (reduced and oxidized).

Flavin adenine dinucleotide reduced form FADH2... 

Direct hydroxylation of an aromatic ring to yield a hydroxybenzene (a phenol) is difficult and rarely done in the laboratory., but occurs much more frequently in biological pathways. An example is the hydroxylation of p-hydroxyphenyl acetate to give 3,4-dihydroxyphenyl acetate. The reaction is catalyzed by p-hydroxyphenylacctate-3-hydroxylase and requires molecular oxygen plus the coenzyme reduced flavin adenine dinucleotide, abbreviated FADH2. 

Step 1 of Figure 29.3 Introduction of a Double Bond The /3-oxidation pathway begins when a fait)7 acid forms a thioester with coenzyme A to give a fatty acyl Co A. Two hydrogen atoms are then removed from C2 and C3 of the fatty acyl CoA by one of a family of acyl-CoA dehydrogenases to yield an a,/3-unsaturated acyl CoA. This kind of oxidation—the introduction of a conjugated double bond into a carbonyl compound—occurs frequently jn biochemical pathways and usually involves the coenzyme flavin adenine dinucleotide (FAD). Reduced FADH2 is the by-product. 

So what does riboflavin do As such riboflavin does nothing. Like thiamine, riboflavin must undergo metabolic change to become effective as a coenzyme. It fact, it undergoes two reactions. The first converts riboflavin to riboflavin-5-phosphate (commonly known as flavin adenine mononucleotide, FMN), about which we will say no more, and the second converts it to flavin adenine dinucleotide, FAD. The flavins are a class of redox agents of very general importance in biochemistry. FAD is the oxidized form and FADH2 is the reduced form. ... 

Scheme 2. Structures of oxidized (FAD) and reduced (FADH2) forms of flavin adenine dinucleotide.

Another important oxidizing agent in biological systems is flavin adenine dinucleotide, FAD. Like NAD , it is a two-electron acceptor, but unlike NAD , it accepts two electrons as 2H- rather than as H . The reduced form, FADH2, has the hydrogens at ring nitrogens ... 

Amperometric biosensors based on flavin-containing enzymes have been studied for nearly 30 years. These sensors typically undergo several chemical or electrochemical steps which produce a measurable current that is related to the substrate concentration. In the initial step, the substrate converts the oxidized flavin adenine dinucleotide (FAD) center of the enzyme into its reduced form (FADH2). Because these redox centers are essentially electrically insulated within the enzyme molecule, direct electron transfer to the surface of a conventional electrode does not occur to a substantial degree. The classical" methods (1-4) of indirectly measuring the amount of reduced enzyme, and hence the amount of substrate present, rely on the natural enzymatic reaction ... 

FAD (flavine adenine dinucleotide) is located at the enzyme s active site (as). In oxidizing glucose, the cofactor is reduced to FADH2, but the oxidized form of an appropriate mediator (Mox) has a redox potential sufficient to re-oxidize the cofactor whilst itself being reduced. In its simplest embodiment, the reduced mediator (Mred) diffuses from the active site at the enzyme to an electrode surface poised at a potential sufficiently oxidizing to re-oxidize the mediator ... 

Fig. 3. Reduced forms of flavin adenine dinucleotide, (a) FADH2. (b) Neutral semiquinone radical.

Flavin adenine dinucleotide (FAD) and its reduced form dihydroflavin (FADH2) participate in a large number of oxidation/reduction reactions in metabolism150. The structure of the reduced form has a distinct enamine feature that has been hypothesized to participate in covalent bonds with a number of substrates. 

F26BP, fructose-2,6-bisphosphate FA, fatty acid FAD, fatty acid desaturase FADH2/FAD, reduced/oxidized flavin adenine dinucleotide F -ATPase, ATP synthetase F complex FGF, fibroblast growth factor FGF-RTK, fibroblast growth factor receptor tyrosine kinase Fmet, formylmethionine FMNH2/FMN, reduced/oxidized flavin mononucleotide... 

There are many carrier molecules for electrons one is called the nicotinamide adenine dinucleotide (NAD+) and another is the flavin adenine dinucleotide FAD+. The reduced cofactors NADH and FADH2 transfer electrons to the electron transport chain. FMN receives electrons from NADH and passes them to coenzyme Q through Fe-S systems. Coenzyme Q receives electrons from FMN and FADH2 through Fe-S systems. Cytochromes receive electrons from the reduced form of coenzyme Q. Each cytochrome consists of a heme group, and the iron of the heme group is reduced when the cytochrome receives an electron Fe3+ Fe2+. At the end of the electron transfer chain, oxygen is reduced to water. 

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