Nicotinamide-adenine dinucleotide formula

Reduced nicotinamide-adenine dinucleotide (NADH) plays a vital role in the reduction of oxygen in the respiratory chain [139]. The biological activity of NADH and oxidized nicotinamideadenine dinucleotide (NAD ) is based on the ability of the nicotinamide group to undergo reversible oxidation-reduction reactions, where a hydride equivalent transfers between a pyridine nucleus in the coenzymes and a substrate (Scheme 29a). The prototype of the reaction is formulated by a simple process where a hydride equivalent transfers from an allylic position to an unsaturated bond (Scheme 29b). No bonds form between the n bonds where electrons delocalize or where the frontier orbitals localize. The simplified formula can be compared with the ene reaction of propene (Scheme 29c), where a bond forms between the n bonds. 

Figure 4.7 Structural formula of nicotinamide adenine dinucleotide in its reduced form of NADH + H+ and its oxidized form NAD+.

An important aspect of enzymatic oxidation-reduction reactions involves the transfer of hydrogen atoms. This transfer is mediated by coenzymes (substances that act together with enzymes) nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These two species pick up H atoms to produce NADH and NADPH, respectively, both of which can function as hydrogen atom donors. Another pair of species involved in oxidation-reduction processes by hydrogen atom transfer consists of flavin adenine triphosphate (FAD) and its hydrogenated form FADH2. The structural formulas of NAD and its cationic form, NAD+, are shown in Figure 4.7. 

Figure 1. Structural formulae (/3-form shown) and overall redox reaction of nicotinamide adenine dinucleotide, NAD+, and its reduced form, the enzymatically active 1,4-NADH. Reproduced with permission from ref. 35. Copyright 1991 Elsevier Science Publishers.

As we pointed out, however, the electrons will not flow unless they have someplace to go. In the light phase of photosynthesis, the electrons moving down the electron transport chain are taken up by nicotinamide adenine dinucleotide phosphate, a molecule with nearly as many symbols in its formula as letters in its unwieldy name. Luckily, it suffices to refer to this entity by its initials, NADP+, a practice common in the complicated world of biochemistry. 

Rgure 2 Structural formulae of two enzyme cofactors (A) nicotinamide adenine dinucleotide (NAD) and (B) flavin adenine dinucleotide (FAD) with the corresponding redox transformations in dehydrogenases and oxidases catalyzed reaction, respectively. NAD is a soluble cofactor and it has to be added to the reaction mixture. As shown in Figure 1, FAD is bound to the flavoprotein. 

Nicotinamide adenine dinucleotide, one of the most important coenzymes (Section 24.9) in biological oxidations and reductions, includes both a pyridine derivative (nicotinamide) and a purine derivative (adenine) in its structure. Its formula is shown in Fig. 14.23 as NAD , the oxidized form that contains the pyridinium aromatic ring. The reduced form of the coenzyme is NADH, in which the pyridine ring is no longer aromatic due to presence of an additional hydrogen and two electrons in the ring. 

The pyridine nucleotide cycle. For formulas of intermediates, see L-Tryptophan and Nicotinamide adenine dinucleotide. 

The reactions of photosynthesis can be carried out in the dark by cells of green plants if they are provided with a supply both of ATP and of another substance, NADPH (reduced nicotinamide-adenine dinucleotide phosphate), which has the formula... 

The reduced form of the coenzyme nicotinamide adenine dinucleotide (NAD", Real Life 8-1) is abbreviated NADH. In the presence of a variety of enzyme catalysts, it acts as a biological hydride donor, capable of reducing aldehydes and ketones to alcohols, according to the general formula... 

The formation of nicotinic acid, as important as it is for the synthesis of the two coenzymes nicotinamide-adenine dinucleotide and its phosphate (formulas in Chapt. VI-4), seems to be only a sidepath. The main degradation probably passes from the unstable, unsaturated aminoaldehyde through isomerization to the imino compound and through hydrolysis to the k to compound. The jS-decarboxylation of the latter results in an a-keto aldehyde with six C atoms which is further broken down to glutarate. 

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