Nicotinamide-adenine dinucleotide redox potential

The biological applications of tetrazolium salts are the subject of a textbook.96 Kuhn and Jerchel74 were the first to recognize the utility of tetrazolium salts as indicators in redox enzyme activity, particularly those of the various dehydrogenases. It has been recognized449 that this particular utility of tetrazolium salts is related to the proximity of their redox potentials to those of the hydride transfer systems in biology450 such as nicotinamide adenine dinucleotide, NAD, and its phosphate analogue, NADP. 

A particular half-cell reaction, such as Equation 6.15, can accept or donate electrons. We quantitatively describe this by the redox potential for that reaction, as expressed by Equation 6.9 [Ej = E u — (RT/qF) In (reduced))/(oxidized))]. We will use (NADPH) to represent the activity of all of the various ionization states and complexed forms of the reduced nicotinamide adenine dinucleotide phosphate, and (NADP+) has an analogous meaning for the oxidized component of the NADP+-NADPH couple. For redox reactions of biological interest, the midpoint (standard) redox potential is usually determined at pH 7. By using Equation 6.9, in which the number q of electrons transferred per molecule reduced is 2, we can... 

Electrochemical transformations of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) have been dealt with in several publications, since they are the most important hydrogen carriers. There are reviews on this topic/" The standard redox potential of the NAD(P)H/NAD(P) couple has been found to be —0.32... 

Suitable redox centers can also be inserted in the electrode coating with the aim to catalyze the oxidation or reduction of the product coming from the enzymatic reaction, such as H2O2 or nicotinamide adenine dinucleotide (NADH). This approach may allow the detection of the analyte at potential values where interfering species are not electroactive [107] and, in some cases, has also been proved to improve the electrode sensitivity [119]. Redox mediators can be adsorbed in the interlayer region of the clay [103,105,106,109,118] or constitute the brucite-like layers of conductive LDHs [104, 122]. Alternatively, bi-enzymatic electrode coatings have also been proposed [53, 108]. Organic polymers, namely poly(pyrrole-... 

Arnon and his group have definitively established that ferredoxins (iron-sulfur proteins noted for their strongly electronegative redox potentials) are the primary electron acceptors in photosynthesis, and that they are essential electron carriers for the light-induced generation of reducing power and ATP formed in the processes of cyclic and non-c clic photophosphorylation. Reducing power—either reduced ferredoxin or reduced nicotinamide adenine dinucleotides, NAD(P)H—and ATP constitute the assimilatory power required for the further assimilation in the dark of carbon dioxide, nitrate and sulfate. ... 

Oxidoreductase enzymes include dehydrogenases, reductases, and oxidases that typically contain flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide phosphate (NAD(P)" ), or pyrroloquinohne quinone (PQQ) as redox cofactors. Although some specific enzymes possess cofactors with theoretically low redox potentials, this does not always translate to efficient performance when immobilized onto electrodes for BFCs. The caveat provides a need to study... 

Mediators can be polymerized on the electrode surface prior to enzyme immobilization, co-immobilized with enzyme, or simply added to the fuel solution. Common mediators used in BFC applications include low molecular weight, polymerizable, organic dyes such as methylene green, phenazines, and azure dyes, along with other redox-active compounds such as ferrocene, ferrocene derivalives, and conductive salts [14]. These mediators are often required for nicotinamide adenine dinucleotide (NAD )- and flavin adenine dinucleotide (FAD)-dependent enzymes, such as ADH, ALDH, and GOx. MET has been achieved at both cathodic and anodic interfaces through solution-phase mediators and mediators immobilized in various ways with or near the enzymes themselves [16,17]. However, these mediated systems do have drawbacks in that the species used to assist electron transfer are often not biocompatible, have short lifetimes themselves, or cause large potential losses. Table 5.1 lists common enzyme cofactors that can mediate or undergo DET with an enzyme on the electrode. 

The dehydrogenase has recently been found and studied. It transfers hydrogen from dihydrothioctic acid to nicotinamide-adenine dinucleotide. Peculiarly, it is a flavoprotein but its redox potential (cf. Chapt. X-3) is much farther on the negative side than that of the familiar flavoproteins, so that hydrogen is able to sw itch over to NAD. 

The mitochondrial electron transport chain (ETC) or respiratory chain comprises a series of membrane-bound redox-aetive intermediates including flavoproteins, quinones, cytochromes, and iron-sulfur elusters [9] (Fig. 1). The latter facilitate the thermodynamically controlled transfer of electrons from conjugate redox pairs of low redox potential (E°) [e.g., —320 mV for reduced nicotinamide-adenine dinueleotide/oxidized nieotinamide-adenine dinucleotide (NADH/ NAD )] to the final electron donor, O2 (with a high redox potential of -1-820... 

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