Nicotinamide adenine dinucleotide reduced , biological reductions

Newman, Melvin S., 93 Newman projection, 93 molecular model of, 93 Nicotinamide adenine dinucleotide, biological oxidations with, 625-626 reactions of, 725 structure of, 725, 1044 Nicotinamide adenine dinucleotide (reduced), biological reductions with, 610-611... 

The first step in the biological degradation of lysine is reductive animation with a-ketoglutarate to give saccharopine. Nicotinamide adenine dinucleotide phosphate (NADPH), a relative of NADH, is the reducing agent. Show the mechanism. 

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. 

NADH (reduced nicotinamide adenine dinucleotide) is utilized in biological reductions to deliver hydride to an aldehyde or ketone carbonyl group (see Box 7.6). A proton from water is used to complete the process, and the product is thus an alcohol. The reaction is catalysed by an enzyme called a dehydrogenase. The reverse reaction may also be catalysed by the enzyme, namely the oxidation of an alcohol to an aldehyde or ketone. It is this reverse reaction that provides the dehydrogenase nomenclature. 

NADP Nicotinamide adenine dinucleotide phosphate NADP and the related NAD (the reduced forms are NADPH2 and NADH2) are coenzymes that are involved in diverse oxidation-reduction reactions in biologic systems among the processes that require NADPH2 is the metabolism of many toxicants by microsomal enzymes in the mammalian liver. 

In many enzymatic reactions, and in particular biological reactions, a second substrate must be introduced to activate the enzyme. This substrate, which is referred to as a cofactor or coenzyme even though it is not an enzyme as such, attaches to the enzyme and is most often either reduced or oxidized during the course of the reaction. Many enzymatic reactions require coenzymes, especially to provide the oxidiz-ing/reducing equivalents for oxidations/reductions. An example of the type of system in which a cofactor is used is the formation of ethanol from acetaldehyde in the presence of the enzyme alcohol dehydrogenase (ADH) and the cofactor nicotinamide adenine dinucleotide (NAD) ... 

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. 

Therefore a field test for NO3 was developed with the biological reducing agent p-nicotinamide adenine dinucleotide (NADH, derived from the vitamin niacin) instead of Cd. The enzyme nitrate reductase (Figure 18-12) catalyzes the reduction ... 

The biological reduction of the carbon-carbon double bond can also be brought about. Commonly this is accomplished by transfer of hydrogen (as hydride) from reduced nicotinamide adenine dinucleotide (NADH) and subsequent (or simultaneous) proton transfer, that is. 

Reductive aminations also occur in various biological pathways. In the biosynthesis of the amino acid proline, for instance, glutamate 5-semialdehyde undergoes internal imine formation to give 1-pyrrolinium 5-carboxylate, which is then reduced by nucleophilic addition of hydride ion to the C=N bond. Reduced nicotinamide adenine dinucleotide, NADH, acts as the biological reducing agent. 

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