Flavin adenine dinucleotide forming

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. 

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. 

Flavin adenine dinucleotide Riboflavin 5 -monophosphate Riboflavin 5 -monophosphate, reduced form Fast protein liquid chromatography (Pharmacia)... 

Flavin Adenine Dinucleotide (FAD) (C27 H33 N9 O15P2) is a coenzyme that acts as a hydrogen acceptor in dehydrogenation reactions in an oxidized or reduced form. FAD is one of the primary cofactors in biological redox reactions. 

Complex II contains four peptides, the two largest form succinate dehydrogenase, the largest has covalently boiuid flavin adenine dinucleotide (FAD) which reacts with succinate, and the other has three iron-sulphur centers. Smaller subunits anchor the two larger subunits to the membrane and form the UQ binding site. Ubiquinone is the electron acceptor but complex II does not pump protons (see below). 

Flavoprotein enzymes contain flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD) as prosthetic groups. FMN and FAD are formed in the body from the vitamin riboflavin (Chapter 45). FMN and FAD are usually tighdy—but not covalendy—bound to their respecdve apoenzyme proteins. Metalloflavopro-teins contain one or more metals as essential cofactors. 

Four of the B vitamins are essential in the citric acid cycle and therefore in energy-yielding metabolism (1) riboflavin, in the form of flavin adenine dinucleotide (FAD), a cofactor in the a-ketoglutarate dehydrogenase complex and in succinate dehydrogenase (2) niacin, in the form of nicotinamide adenine dinucleotide (NAD),... 

Figure 17-5. Oxidative decarboxylation of pyruvate by the pyruvate dehydrogenase complex. Lipoic acid is joined by an amide link to a lysine residue of the transacetylase component of the enzyme complex. It forms a long flexible arm, allowing the lipoic acid prosthetic group to rotate sequentially between the active sites of each of the enzymes of the complex. (NAD nicotinamide adenine dinucleotide FAD, flavin adenine dinucleotide TDP, thiamin diphosphate.)...

Riboflavin fulfills its role in metabolism as the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) (Figure 45-10). FMN is formed by ATP-dependent phosphorylation of riboflavin, whereas FAD is synthesized by further reaction of FMN with ATP in which its AMP moiety is transferred to the... 

A homogeneous electrochemical enzyme immunoassay for 2,4-dinitrophenol-aminocaproic acid (DNP-ACA), has been developed based on antibody inhibition of enzyme conversion from the apo- to the holo- form Apoglucose oxidase was used as the enzyme label. This enzyme is inactive until binding of flavin adenine dinucleotide (FAD) to form the holoenzyme which is active. Hydrogen peroxide is the enzymatic product which is detected electrochemically. Because antibody bound apoenzyme cannot bind FAD, the production of HjOj is a measure of the concentration of free DNP-ACA in the sample. 

Under conditions of copper deficiency, some methanotrophs can express a cytosolic, soluble form of MMO (sMMO) (20-23), the properties of which form the focus of the present review. The sMMO system comprises three separate protein components which have all been purified to homogeneity (24,25). The hydroxylase component, a 251 kD protein, contains two copies each of three subunits in an a 82y2 configuration. The a subunit of the hydroxylase houses the dinuclear iron center (26) responsible for dioxygen activation and for substrate hydroxylation (27). The 38.6 kD reductase contains flavin adenine dinucleotide (FAD) and Fe2S2 cofactors (28), which enable it to relay electrons from reduced nicotinamide adenine dinucleotide (NADH) to the diiron center in the... 

Glucose oxidase (GOD) is a typical flavin enzyme with flavin adenine dinucleotide (FAD) as redox prosthetic group. Its biological function is to catalyze glucose to form gluconolaction, while the enzyme itself is turned from GOD(FAD) to GOD(FADH2). GOD was used to prepare biosensors in extensive fields. Many materials that can be used to immobilize other proteins can be suitable for GOD. GOD adsorbed on CdS nanoparticles maintained its bioactivity and structure, and could electrocatalyze... 

Most coenzymes have aromatic heterocycles as major constituents. While enzymes possess purely protein structures, coenzymes incorporate non-amino acid moieties, most of them aromatic nitrogen het-erocycles. Coenzymes are essential for the redox biochemical transformations, e.g., nicotinamide adenine dinucleotide (NAD, 13) and flavin adenine dinucleotide (FAD, 14) (Scheme 5). Both are hydrogen transporters through their tautomeric forms that allow hydrogen uptake at the termini of the quinon-oid chain. Thiamine pyrophosphate (15) is a coenzyme that assists the decarboxylation of pyruvic acid, a very important biologic reaction (Scheme 6). 

EADH2 flavin adenine dinucleotide, reduced form... 

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. ... 

Riboflavin is the redox component of flavin adenine dinucleotide FAD. It is derived from FAD by hydrolysis of a phosphate ester link. The fully oxidised form of FAD is involved in many dehydrogenaze reactions during which it is converted to the fully reduced form. The fully oxidised state is restored either by another redox enzyme or by interaction with oxygen and hydrogen peroxide is liberated. The one-electron reduced, semiquinone form of FAD, is involved in some electron transfer steps. 

There are demethylases which act like amine oxidases that are dependent in their mechanism on their cosubstrate flavine adenine dinucleotide (FAD). So far, lysine-specific demethylase 1 (LSDl) is the only representative of this class [62]. LSDl, as an amine oxidase leads to oxidation of the methylated lysine residue, generating an imine intermediate, while the protein-bound cosubstrate FAD is reduced to FAD H2. In a second step, the imine intermediate is hydrolyzed to produce the demethylated histone lysine residue and formaldehyde. Importantly the reduced cosubstrate is regenerated to its oxidized form by molecular oxygen, producing hydrogen peroxide (Figure 5.7) [62, 63]. 

CoQ Coenzyme Q FADH- Radical form of reduced flavin adenine dinucleotide... 

Riboflavin (vitamin Bj) is chemically specified as a 7,8-dimethyl-10-(T-D-ribityl) isoalloxazine (Eignre 19.22). It is a precnrsor of certain essential coenzymes, such as flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) in these forms vitamin Bj is involved in redox reactions, such as hydroxylations, oxidative carboxylations, dioxygenations, and the reduction of oxygen to hydrogen peroxide. It is also involved in the biosynthesis of niacin-containing coenzymes from tryptophan. 

Riboflavin (vitamin B2) is found in liver, milk, meat, green vegetables, cereals and mushrooms. It is active in the form of two coenzymes, flavin mononucleotide and flavin adenine dinucleotide. As a coenzyme for proton transfer in the respiratory chain it is indispensable for energy-release from carbohydrates, lipids and proteins. Riboflavin deficiency only occurs in combination with deficiencies of other members of the vitamin B family. The symptoms of such deficiency consist of angular stomatitis, lesions of the cornea, dermatoses and normochromic normocytic anaemia. 

The oxidations are performed in aqueous buffer solution at pH 9.0 with less than stoichiometric amounts of nicotineamide adenine dinucleotide (NAD+) as coenzyme, which is expensive and therefore must be recycled. This can be done in such oxidations in several ways. The simplest is to simultaneously oxidize the reduced nicotineamide adenine dinucleotide formed with a stoichiometric amount (based on the diol) of inexpensive flavin adenine mononucleotide (FMN)167. In this manner gram quantities of the corresponding lactone may be readily obtained scaling up the reaction, however, seems to be a problem167. 

It carries its physiological function in its active forms, flavin mononucleotide (FMN) and flavin adenine dinucleotide. These coenzymes are involved in various biochemical reactions. 

Most presently available MAOIs are irreversible inhibitors of the enzyme, forming a chemical bond with part of the enzyme or the flavin adenine dinucleotide cofactor. When treatment is stopped, inhibition continues for a time until MAO levels return to normal as the new enzyme is synthesized. Thus, phenelzine, isocarboxazid, and tranylcypromine are all irreversible, nonselective MAOIs. Clorgyline, however, is an irreversible, selective MAO-A inhibitor moclobemide is a reversible, selective MAOI l-deprenyl and pargyline are relatively selective, irreversible MAO-B inhibitors. 

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