Vitamins flavins

Paul Karrer chemistry research iato constitution of carotenoids, flavins, and vitamins A and B2... 

Polarography is appHed in the presence of other vitamins, eg, in multivitamin tablets, without separation. The polarography of flavins is reviewed in Reference 71. 

Riboflavin-5 -Phosphate. Riboflavin-5 -phosphate [146-17-8] (vitamin B2 phosphate, flavin mononucleotide, FMN, cytoflav), C2yH22N402P,... 

Riboflavin (vitamin Bg) Nicotinamide adenine dinncleotide phosphate (NADP+) Flavin adenine dinncleotide (FAD)... 

Several classes of vitamins are related to, or are precursors of, coenzymes that contain adenine nucleotides as part of their structure. These coenzymes include the flavin dinucleotides, the pyridine dinucleotides, and coenzyme A. The adenine nucleotide portion of these coenzymes does not participate actively in the reactions of these coenzymes rather, it enables the proper enzymes to recognize the coenzyme. Specifically, the adenine nucleotide greatly increases both the affinity and the speeifieity of the coenzyme for its site on the enzyme, owing to its numerous sites for hydrogen bonding, and also the hydrophobic and ionic bonding possibilities it brings to the coenzyme structure. 

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. 

Pantothenic acid, sometimes called vitamin B3, is a vitamin that makes up one part of a complex coenzyme called coenzyme A (CoA) (Figure 18.23). Pantothenic acid is also a constituent of acyl carrier proteins. Coenzyme A consists of 3, 5 -adenosine bisphosphate joined to 4-phosphopantetheine in a phosphoric anhydride linkage. Phosphopantetheine in turn consists of three parts /3-mercaptoethylamine linked to /3-alanine, which makes an amide bond with a branched-chain dihydroxy acid. As was the case for the nicotinamide and flavin coenzymes, the adenine nucleotide moiety of CoA acts as a recognition site, increasing the affinity and specificity of CoA binding to its enzymes. 

Walter Haworth and Paul Karrer (W. H.) investigations on carbohydrates, vitamin C and (P. K.) investigation of carotenoids, flavins, and vitamins A and B2... 

Vitamin B2 or riboflavin is chemically defined as 7,8-dimethyl-10-(lY-D-tibityl)isoalloxazine. Figure 1 shows the oxidized and reduced form of the vitamin. The ending flavin (from the latin word flavus—yellow) refers to its yellowish color. 

Vitamin B2. Figure 2 Structure of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). 

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),... 

Flavins — Riboflavin is first of all essential as a vitamin for humans and animals. FAD and FMN are coenzymes for more than 150 enzymes. Most of them catalyze redox processes involving transfers of one or two electrons. In addition to these well known and documented functions, FAD is a co-factor of photolyases, enzymes that repair UV-induced lesions of DNA, acting as photoreactivating enzymes that use the blue light as an energy source to initiate the reaction. The active form of FAD in photolyases is their two-electron reduced form, and it is essential for binding to DNA and for catalysis. Photolyases contain a second co-factor, either 8-hydroxy-7,8-didemethyl-5-deazariboflavin or methenyltetrahydrofolate. ... 

Here we will present some basic theoretical photochemistry of a set of furocoumarin compounds, starting from the basic building blocks furan and pyrone, as shown in Fig. 4.13. Comparison is also made with the photochemistry of flavin, the active component of vitamin B2. 

Flavins and their analogues (vitamin B2 family) bound to a cationic hydrophobic aggregate serve as efficient oxidizing agents for carbanions and thiols (see Section 7). 

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. 

Examples of coenzymes vitamin-derived nucleotides for example adenosine phosphates ATP, ADP, AMP nicotinamide derivatives NAD+, NADH, NADP+, NADPH flavin derivatives FAD, FADH2 coenzyme A (abbreviated to CoA, CoASH or CoA-SH). 

The cases of myoglobin and hemoglobin are not rare. Many enzymes are dependent for their function on the presence of a nonprotein group. For example, cytochrome c also contains a prosthetic group similar, but not identical, to heme, as do a number of other proteins. These are known generically as heme proteins. There is a family of enzymes that contain a flavin group, the flavoproteins. Another family contains pyridoxal phosphate, a derivative of vitamin Be. There are a number of other examples. 

Vitamin B2, or riboflavin, is the metabolic precursor to two flavin coenzymes essential for the integrity of a spectrum of redox reactions. 

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. 

In the reduction or oxidation of quinone/ quinol systems, free radicals also appear as intermediate steps, but these are less reactive than flavin radicals. Vitamin E, another qui-none-type redox system (see p.l04), even functions as a radical scavenger, by delocalizing unpaired electrons so effectively that they can no longer react with other molecules. 

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 (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. 

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). 

Product Retinol [Pg.211]

Ehrenberg, A. Flavin radical-metal chelates. In Vitamins and hormones, Vol. 28 (Harris, R. S., Munson, P. L., Diezfalusy, E. eds.) pp. 489-503, New York, London, Academic Press 1970... 

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). 

Pteridines, Alloxazines, Flavins, Vitamin B2 and Related Compounds Vitamin Bj and Related Compounds , G. R. Ramage and T. S. Stevens, in The Chemistry of Carbon Compounds , ed. E. H. Rodd, Elsevier, Amsterdam, 1960, vol. 4C, pp. 1760-1798. 

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