Riboflavin adenine dinucleotide

The first to be isolated of those complexes which enzymes form with their substrates was the complex of D-alanine, D-amino acid oxidase, and its co-factor FAD (riboflavine adenine dinucleotide). It consisted of hexagonal purple crystals and was stable in the absence of air. Electron spin resonance measurements showed that the co-factor, present in these crystals, was in its free-radical monohydro-form (FADH) (Yagi, 1965). 

With another molecule of ATP FMN yields riboflavin adenine dinucleotide (FAD). FAD may be covalently bound to enzyme proteins at one of the methyl groups (Fig. 179). Acceptors are one of the ring iV-atoms of a special L-histidinyl or the S-atom of a special L-cisteinyl residue. 

Riboflavin-5 -Adenosine Diphosphate. Riboflavin-5 -adenosine diphosphate [146-14-5] (flavin—adenine dinucleotide, FAD), C27H33N9O15P2 (2), mol wt 785.56, was first isolated in 1938 from the D-amino acid oxidase as its prosthetic group (95), where it was postulated to be... 

Riboflavin, or vitamin B2, is a constituent and precursor of both riboflavin 5 -phosphate, also known as flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). The name riboflavin is a synthesis of the names for the molecule s component parts, ribitol and flavin. The structures of riboflavin. 

The fused system, pyrimido[4,5-h]pyrazine (219), is more commonly known as pteridine, a ring system which is present in such biologically important molecules as alloxazine, riboflavin, leucopterin, xanthopterin, and the coenzyme, flavin-adenine dinucleotide. 

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

Riboflavin is heat-stable in the absence of light, but extremely photosensitive. It has a high degree of natural fluorescence when excited by UV light. This property can be used for detection and determination. Two coenzymes (Fig. 2), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), are derived from riboflavin. 

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),... 

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... 

Figure45-10. Riboflavin and the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

FIGURE 10.1 The structural formula of riboflavin and partial structures of riboflavin compounds. The latter show only those portions of the molecule that differ from riboflavin. 1 — Riboflavin (RF), 2 — flavin mononucleotide or 5 -riboflavin monophosphate (FMN or 5 -FMN), 3 — flavin adenine dinucleotide (FAD). 

HPLC with fluorescence detection was employed for the analysis of riboflavin (RF), flavin mononucleotide (FMN) and flavin-adenin dinucleotide (FAD) in beer, wine and other beverages. The investigation was motivated by the finding that these compounds are responsible for the so-called taste of light which develops in beverages exposed to light. Samples were filtered and injected in to the analytical column without any other pretreatment. Separations were carried out in an ODS column (200 X 2.1mm i.d. particle size 5 pm). Solvents A and B were 0.05 M phosphate buffer (pH 3) and ACN, respectively. The... 

C. Andres-Lacueva, F. Mattivi and D. Tonon, Determination of riboflavin, flavin mononucleotide and flavin-adenin dinucleotide in wine and other beverages by high-performance liquid chromatography with fluorescence detection. J. Chromatogr.A 823 (1998) 355-363. 

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 (vitamin B2) is a component of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), coenzymes that play a major role in oxidation-reduction reactions (see Section 15.1.1). Many key enzymes involved in metabolic pathways are actually covalently bound to riboflavin, and are thus termed flavoproteins. 

Riboflavin (from the Latin flavus, yellow) serves in the metabolism as a component of the redox coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD see p. 104). As prosthetic groups, FMN and FAD are cofactors for various oxidoreductases (see p. 32). No specific disease due to a deficiency of this vitamin is known. 

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. 

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. 

Riboflavin (B2) Flavin adenine dinucleotide flavin mononucleotide Carbohydrate metabolism... 

Vitamin Bj (8.44, riboflavin) is a benzopteridine derivative carrying a ribityl (reduced ribose) side chain. It occurs in almost all foods, the largest amounts being found in eggs, meat, spinach, liver, yeast, and milk. Riboflavin is one of the major electron carriers as a component of flavine-adenine dinucleotide (FAD), which is involved in carbohydrate and fatty acid metabolism. A hydride ion and a proton are added to the pyrazine ring of... 

Riboflavin (vitamin B2 6.18) consists of an isoalloxazine ring linked to an alcohol derived from ribose. The ribose side chain of riboflavin can be modified by the formation of a phosphoester (forming flavin mononucleotide, FMN, 6.19). FMN can be joined to adenine monophosphate to form flavin adenine dinucleotide (FAD, 6.20). FMN and FAD act as co-enzymes by accepting or donating two hydrogen atoms and thus are involved in redox reactions. Flavoprotein enzymes are involved in many metabolic pathways. Riboflavin is a yellow-green fluorescent compound and, in addition to its role as a vitamin, it is responsible for the colour of milk serum (Chapter 11). 

Babior, who has studied this enzyme at several stages of its purification, found in lysates of PMNs which were activated with zymosan that of eight potential biological reductants only reduced pyridine nucleotides supported the formation of O ". The K , for NADPH was less than the K , for NADH and the activity was decreased in preparations from three patients with chronic granulomatous disease. In accord with predictions based on reaction 7, 0.55 molecule of O7 was measured per molecule of NADPH oxidized under conditions of saturating concentrations of cytochrome c The enzyme which was extracted with Triton X-100 from a granule-rich fraction from activated PMNs, required an external source of FAD for the formation of O from NADPH . Riboflavin and FMN would not substitute. Flavin adenine dinucleotide was proposed as a necessary cofactor, which was probably lost when the enzyme was treated with the detergent. 

The combined dehydrogenation and decarboxylation of pyruvate to the acetyl group of acetyl-CoA (Fig. 16-2) requires the sequential action of three different enzymes and five different coenzymes or prosthetic groups—thiamine pyrophosphate (TPP), flavin adenine dinucleotide (FAD), coenzyme A (CoA, sometimes denoted CoA-SH, to emphasize the role of the —SH group), nicotinamide adenine dinucleotide (NAD), and lipoate. Four different vitamins required in human nutrition are vital components of this system thiamine (in TPP), riboflavin (in FAD), niacin (in NAD), and pantothenate (in CoA). We have already described the roles of FAD and NAD as electron carriers (Chapter 13), and we have encountered TPP as the coenzyme of pyruvate decarboxylase (see Fig. 14-13). 

Dioxetanes are readily reduced to 1,2-diols (Scheme 30) by lithium aluminum hydride (75CJC1103), thiols (88AG(E)429), and biologically important reductants (89MI 133-02) such as ascorbic acid, tocopherol, dihydronicotinamide adenine dinucleotide (NADH), and riboflavin adenosine diphosphate (FADH2). 

Riboflavin Flavin mononucleotide Flavin adenine dinucleotide... 

Flavin adenine diphosphate (FAD, flavin adenine dinucleotide) and riboflavin 5 -monophosphate (FMN, flavin mononucleotide), whose structures are shown in Fig. 15-7, are perhaps the most versatile of all... 

In the biological oxidation-reduction system, reduced NAD (i.e., NADH) is reoxidized to NAD by the riboflavin-containing coenzyme FAD flavin-adenine dinucleotide). 

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