Dehydrogenases nicotinamide mononucleotide

Both groups of reactions are found in bacteria (14), all higher animals (i5), and plants (16) however, oxidative phosphorylation is responsible for 90 % of the oxygen consumed (i 7). Oxidative phosphorylation is driven by the respiratory electron-transport system that is embedded in the lipoprotein inner membrane of eukaryotic mitochondria and in the cell membrane of prokaryotes. It consists of four complexes (Scheme I). The first is composed of nicotinamide adenine dinucleotide (NADH) oxidase, flavin mononucleotide (FMN), and nonheme iron-sulfur proteins 18,19), and it transfers electrons from NADH to ubiquinone. The second is composed of succinate dehydrogenase (SDH), flavin adenine dinucleotide (FAD), and nonheme iron-sulfur proteins (20), and it transfers electrons from succinate to ubiquinone 21, 22). The third is composed of cytochromes b and c, and nonheme iron-sulfur proteins (23), and it transfers electrons from ubiquinone (UQ) to cytochrome c 24). The fourth complex consists of cytochrome c oxidase [ferrocytochrome c 0 oxidoreductase EC 1.9.3.1 25)] which transfers electrons from cytochrome c to O2 26, 27). 

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+. 

Oxidoreductase dehydrogenase and flavoenzymes. Nicotinamide adenine dinucleotide (NAD+)/nicotinamide adenine dinucleotide phosphate (NADF) and flavin mononucleotide (FMN)/flavin adenine dinucleotide (FAD) are the two major types of redox coenzymes. 

Enzyme purification was the first application of bioaffinity chromatography [23] and remains an important use of this technique. In this type of separation, ligands, such as enzyme inhibitors, coenzymes, or cofactors, are used to purify and separate enzymes [25]. For instance, in 1968 and the first report of "modem" affinity chromatography, Cuatrecasas, Wilchek, and Anfinsen employed specific enzyme inhibitors to selectively isolate enzymes [1,4]. A more recent example was the use of a support containing flavin mononucleotides for the purification of flavin adenine dinucleotide synthetase [26]. Other examples have included the use of mono-, di-, and triphosphate nucleotides for the purification of kinases and the use of nicotinamide adenine dinucleotide for the isolation of dehydrogenases [26,27]. 

HLADH, horse liver alcohol dehydrogenase (3-NAD, nicotinamide adenine dinucleotide FMN, flavin mononucleotide... 

In contrast, alcohol dehydrogenase (ADH) requires a coenzyme, nicotinamide adenine dinucleotide (NAD), whose reduced form (NADH) cannot be oxidized by oxygen. An electioactive species must act as a mediator u> le noate NAD. A variety of substances have been tested as mediators [168], phenazine methosulfate (PMS) rapidly oxidizes NADH but is unstable, and thioglycdate and methyl violet react too slowly. Flavin mononucleotide (FMN), however, is easily oxidized at the anode by a constant current, and NAD can be regenerated. Hence, ethanol is determined using the three following reactions ... 

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