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Nicotinamide coenzyme forms

Nicotinamide and nicotinic acid are both white crystalline substances. Their aqueous solution has a maximal UV absorbance at 263 nm. Both vitamers have the same biological activity as they can be converted into each other. Figure 2 shows the structure of the coenzyme forms NAD+ and NADP+. [Pg.850]

Most foods of animal origin contain nicotinamide in the coenzyme form (high bioavialability). Liver and meat are particularly rich in highly bioavailable niacin. Most of the niacin in plants, however, occurs as nicotinic acid in overall lower concentrations and with a lower bioavailability. The major portion of niacin in cereals is found in the outer layer and its bioavailability is as low as 30% because it is bound to protein (niacytin). If the diet contains a surplus of L-tryptophan (Ttp), e.g., more than is necessary for protein synthesis, the liver can synthesize NAD from Trp. Niacin requirements are therefore declared as niacin equivalents (1 NE = 1 mg niacin = 60 mg Trp). [Pg.850]

Like the nicotinamide coenzymes (Fig. 13-15), the flavin nucleotides undergo a shift in a major absorption band on reduction. Flavoproteins that are fully reduced (two electrons accepted) generally have an absorption maximum near 360 nm. When partially reduced (one electron), they acquire another absorption maximum at about 450 nm when fully oxidized, the flavin has maxima at 370 and 440 nm. The intermediate radical form, reduced by one electron, has absorption maxima at 380, 480, 580, and 625 nm. These changes can be used to assay reactions involving a flavoprotein. [Pg.515]

Two derivatives of nicotinamide (pyridine-3-carboxylic amide), one of the B2 vitamins, nicotinamide adenine dinucleotide (NAD ) and nicotinamide adenine dinucleotide phosphate (NADP ), serve as redox coenzymes. Of the three heterocyclic ring systems found in these coenzymes, i.e. those of purine, ribose and pyridine, it is the pyridine portion that is reactive in redox reactions. Biologically, two oxidation states are important the oxidized form, NAD(P)+, and the 1,4-dihydro isomer of the two-electron reduced form, NAD(P)H (Scheme 1). Nicotinamide coenzymes interconvert between these two oxidation states in... [Pg.248]

NAD+ and NADP+. This difference reflects the chemical difference between the vitamins riboflavin and nicotinamide which form the oxidation-reduction centers of the coenzymes. Another difference is that NAD+ and NADP+ tend to be present in free forms within cells, diffusing from a site on one enzyme to a site on another. These coenzymes are sometimes tightly bound but flavin coenzymes are usually firmly bound to proteins, fixed, and unable to move. Thus, they... [Pg.766]

The catalytic effect of metal ions such as Mg2+ and Zn2+ on the reduction of carbonyl compounds has extensively been studied in connection with the involvement of metal ions in the oxidation-reduction reactions of nicotinamide coenzymes [144-149]. Acceleration effects of Mg2+ on hydride transfer from NADH model compounds to carbonyl compounds have been shown to be ascribed to the catalysis on the initial electron transfer process, which is the rate-determining step of the overall hydride transfer reactions [16,87,149]. The Mg2+ ion has also been shown to accelerate electron transfer from cis-dialkylcobalt(III) complexes to p-ben-zoquinone derivatives [150,151]. In this context, a remarkable catalytic effect of Mg2+ was also found on photoinduced electron transfer reactions from various electron donors to flavin analogs in 1984 [152], The Mg2+ (or Zn2+) ion forms complexes with a flavin analog la and 5-deazaflavins 2a-c with a 1 1 stoichiometry in dry MeCN at 298 K [153] ... [Pg.143]

The nicotinamide coenzymes are biological carriers of reducing equivalents (electrons). The most common function of NAD+ is to accept two electrons and a proton (H equivalent) from a substrate undergoing metabolic oxida-tion to produce NADH, the reduced form of the coenzyme. This then diffuses or is transported to the terminal-electron transfer sites of the cell and reoxidized by terminal-electron acceptors, 02 in aerobic organisms, with the concomitant formation of ATP (chapter 14). Equations (8), (9), and (10) are typical reactions in which NAD+ acts as such an acceptor. [Pg.203]

Tetrahydrofolate functions as a carrier of one-carbon units. There are numerous metabolic reactions that require either the addition or removal of a one-carbon unit of some specific oxidation state. THF binds one-carbon units of three oxidation levels the methanol, formaldehyde, and formate states. These are shown in Table 6.4 along with their origins and uses. The various one-carbon units are interconvertible, as shown in Figure 6.5. Nicotinamide coenzymes are involved. In addition, the one-carbon unit may be released as C02. The methanol-level THF-bound one-carbon unit 5-methyl-THF is the storage and transport form. Once formed, its main pathway of metabolism is to form methionine from homocysteine, a reaction that requires vitamin B12 in the form of methylcobalamin (see Figure 6.2 and Chapter 20) ... [Pg.136]

The term niacin refers to nicotinic acid (pyridine-3-carboxyhc acid), its amide nicotinamide, and derivatives that show the same biological activity as nicotinamide. A distinction between the two primary vitamin forms has to be considered, however, when considering some aspects of their metabolism and especially their different pharmacological actions at high doses. Structures of both vitamers and the two coenzyme forms containing the nicotinamide moiety are given in Figure 30-23. [Pg.1114]

Niacin (nicotinic acid pyridine-3-carboxylic acid) and nicotinamide are precursors of NAD+ and NADP+ (Figure 38-19). Niacin occurs in meat, eggs, yeast, and whole-grain cereals in conjunction with other members of the vitamin B group. Little is known about absorption, transport, and excretion of niacin and its coenzyme forms. A limited amount of niacin can be synthesized in the body from tryptophan, but it is not adequate to meet metabolic needs. [Pg.924]

The answer is b. (Murray, pp 627-661. Scriver, pp 3897-3964. Sack, pp 121-138. Wilson, pp 287-320.) Nicotinamide adenine dinucleotide (NAD+) is the functional coenzyme derivative of niacin. It is the major electron acceptor in the oxidation of molecules, generating NADH, which is the major electron donor for reduction reactions. Thiamine (also known as vitamin Bi) occurs functionally as thiamine pyrophosphate and is a coenzyme for enzymes such as pyruvate dehydrogenase. Riboflavin (vitamin B2) functions in the coenzyme forms of flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD). When concentrated, both have a yellow color due to the riboflavin they contain. Both function as prosthetic groups of oxidation-reduction enzymes or flavoproteins. Flavoproteins are active in selected oxidation reactions and in electron transport, but they do not have the ubiquitous role of NAD+. [Pg.265]

Nicotinamide adenine dinucleotide (NAD) is the coenzyme form of the vitamin niacin. Most biochemical reactions require protein catalysts (enzymes). Some enzymes, lysozyme or trypsin, for example, catalyze reactions by themselves, but many require helper substances such as coenzymes, metal ions, and ribonucleic acid (RNA). Niacin is a component of two coenzymes NAD, and nicotinamide adenine dinucleotide phosphate (N/kDP). NAD (the oxidized form of the NAD coenzyme) is important in catabolism and in the production of metabolic energy. NADP (the oxidized form of NADP) is important in the biosynthesis of fats and sugars. [Pg.845]

NAD, NADH, NADP, NADPH. Abbreviations for nicotinamide adenine dinucleotide [phosphate] in the oxidized and reduced forms, see nicotinamide coenzymes. [Pg.420]

The development of chemically modified electrodes, CMEs, has now reached a level of maturity which allows the inclusion of such electrochemical cells into various sensing devices. Special interest has been focused on the electron transfer or rather the hindrances for electron transfer during bioelectrochemical reactions. Studies of the oxidation of the reduced form of the nicotinamide coenzymes NADH and NADPH are attractive because a single electrochemical transducer reaction can be combined with any of the great number of dehydrogenases to give a sensor with the desired selectivity. [Pg.183]

Two nicotinamide coenzymes, jff-nicotinamide adenine dinucleotide (NAD" ) and jff-nicotinamide adenine dinucleotide phosphate (NADP" ), have closely related structures (Fig. 9.9) and electrochemical properties. Although generally represented as cations, it is worth pointing out that in both cases the oxidized forms of coenzymes are anionic at neutral pH due to ionization of phosphate groups in the... [Pg.243]

Nicotinic acid and nicotinamide These are sometimes known by the generic term niacin. Their importance is in combination with tryptophan, as the coenzyme forms nicotinamide adenine dinucleotide (NAD + ) and nicotinamide adenine dinucleotide phosphate (NADP). HPLC is too insensitive to measure endogenous plasma levels, but the urinary metabolites N-methyl-2-pyridone-5-carboxylamide and N -methylnicotinamide can be measured to assess niacin status. Preliminary cleanup of urine by anion-exchange resins is followed by reversed-phase HPLC with UV detection. [Pg.2705]

While it is doubtful if cystine, the disulphide of cysteine, has any critical biological role as such, it is an ubiquitous constituent of aerobic systems resulting from the facile oxidation of cysteine. It also can arise from the digestion of protein disulphides. Cystine is relatively insoluble and if allowed to build up tends to form crystalline precipitates within the cell. There is normally little of the disulphide in cells, while in the blood the oxidized form dominates. One method for the reduction of cystine to cysteine is via a nicotinamide coenzyme-linked dehydrogenase. Glutathione... [Pg.313]

There are two different forms of the nicotinamide coenzymes jS-NAD" " and J0-NADP+. They have closely related structures, both revealed in Eig. 1, and unique electrochemical properties. In solution, NAD+ acquires a folded conformation as suggested from circular dichroism [4], fluorescence spectroscopy [5], NMR [6-8], and X-ray crystallography [9] experiments. [Pg.5369]

From a nutritional standpoint, it is significant that five of the B-complex vitamins (riboflavin, nicotinamide, thiamine, vitamin Be, and pantothenic acid) have been shown to be constituents of the coenzymes. The nutritional requirement of these vitamins is explained on the basis of their coenzyme function. In all cases the coenzyme form appears to be the sole bound form of the vitamin, and this then becomes the only metabolically active form for these particular vitamins. [Pg.329]

Although DPN is the older of the two coenzymes in point of historical recognition, its partner, TPN, was the first of the pair to be isolated, in the classical investigations of Warburg and his co-workers. Shortly thereafter, DPN was isolated by von Euler and his school. It is interesting to note that nicotinamide was recognized as a component of these coenzymes before the acid of this amide was discovered to be a nutritionally important vitamin. This represents the only case in which the coenzyme form of a vitamin was recognized before the vitamin function was discovered, a point which further emphasizes the close correlation between the fields of nutrition and of enzyme chemistry. [Pg.332]


See other pages where Nicotinamide coenzyme forms is mentioned: [Pg.226]    [Pg.58]    [Pg.69]    [Pg.474]    [Pg.377]    [Pg.533]    [Pg.252]    [Pg.148]    [Pg.2404]    [Pg.232]    [Pg.1115]    [Pg.185]    [Pg.1039]    [Pg.259]    [Pg.399]    [Pg.259]    [Pg.150]    [Pg.92]    [Pg.311]    [Pg.340]    [Pg.13]    [Pg.222]   
See also in sourсe #XX -- [ Pg.203 , Pg.204 , Pg.206 , Pg.206 ]




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