NADP+ nicotinamide adenine dinucleotide reduction

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. 

Nicotinamide is the reactive moiety of the nicotinamide nucleotide coenzymes NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate), which are coenzymes (or more correctly cosubstrates) in a wide variety of oxidation and reduction reactions (Section 8.4.1). The notation NAD(P) is used to mean either NAD or NADP, without specifying the oxidation state. 

In photosystem II electrons that lost part of their energy during photoreaction I take up energy again, the energy being used for the reduction of NADP (nicotinamide adenine dinucleotide diphosphate) in photoreaction II. NADPHj formed is a stable transport metabolite of hydrogen. 

The free hydrogen is used for carbon reduction according to Equation (2.42). The process is complex (called the Cabin cycle) and the starting point is the transfer of H onto NADP" (nicotinamide adenine dinucleotide phosphate C2iH29N70i7P3), which is the oxidized form of NADPH (which is the reduced form of NADP-") ... 

Whereas catabolism involves oxidation of starting molecnles, biosynthesis or anabolism involves reduction reactions, hence the need for a reducing agent or hydrogen donor, which is usually NADP (nicotinamide adenine dinucleotide phosphate). These catalysts are known as coenzymes and the most widely occurring is coenzyme A (CoA), made up of ADP (adenosine diphosphate) and pantetheine phosphate. 

NADP Nicotinamide adenine dinucleotide phosphate Niacin Oxidation and reduction reactions... 

In oiological systems, the most frequent mechanism of oxidation is the remov of hydrogen, and conversely, the addition of hydrogen is the common method of reduc tion. Nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP) are two coenzymes that assist in oxidation and reduction. These cofactors can shuttle between biochemical reac tions so that one drives another, or their oxidation can be coupled to the formation of ATP. However, stepwise release or consumption of energy requires driving forces and losses at each step such that overall efficiency suffers. 

Nicotinamide is an essential part of two important coenzymes nicotinamide adenine dinucleotide (NAD ) and nicotinamide adenine dinucleotide phosphate (NADP ) (Figure 18.19). The reduced forms of these coenzymes are NADH and NADPH. The nieotinamide eoenzymes (also known as pyridine nucleotides) are electron carriers. They play vital roles in a variety of enzyme-catalyzed oxidation-reduction reactions. (NAD is an electron acceptor in oxidative (catabolic) pathways and NADPH is an electron donor in reductive (biosynthetic) pathways.) These reactions involve direct transfer of hydride anion either to NAD(P) or from NAD(P)H. The enzymes that facilitate such... 

For the majority of redox enzymes, nicotinamide adenine dinucleotide [NAD(H)j and its respective phosphate [NADP(H)] are required. These cofactors are prohibitively expensive if used in stoichiometric amounts. Since it is only the oxidation state of the cofactor that changes during the reaction, it may be regenerated in situ by using a second redox reaction to allow it to re-enter the reaction cycle. Usually in the heterotrophic organism-catalyzed reduction, formate, glucose, and simple alcohols such as ethanol and 2-propanol are used to transform the... 

Although the structures for molecules having niacin activity are simple, the forms in which they act in human biochemistry are not so simple. Nicotinic acid and nicotinamide are precursors for three complex coenzymes in multiple oxida-tion/reduction (redox) reactions nicotinamide mononucleotide, NMN nicotinamide adenine dinucleotide, NAD+ and nicotinamide adenine dinucleotide phosphate, NADP. I shall use NAD+ as representative of the class. NADH is the corresponding reduced form. ... 

FIGURE 13-15 NAD and NADR (a) Nicotinamide adenine dinucleotide, NAD +, and its phosphorylated analog NADP+ undergo reduction to NADH and NADPH, accepting a hydride ion (two electrons and one proton) from an oxidizable substrate. The hydride ion is added to either the front (the A side) or the back (the B side) of the planar nicotinamide ring (seeTable 13-8). (b)The UV absorption spec-... 

Two vitamins, nicotinamide and pyridoxine (vitamin B6), are pyridine derivatives. Nicotinamide participates in two coenzymes, coenzyme I (65 R = H) which is known variously as nicotinamide adenine dinucleotide (NAD) or diphosphopyridine nucleotide (DPN), and coenzyme II (65 R = P03H2) also called triphosphopyridine nucleotide (TPN) or nicotinamide adenine dinucleotide phosphate (NADP). These are involved in many oxidation-reduction processes, the quaternized pyridine system acting as a hydrogen acceptor and hydrogen donor. Deficiency of nicotinamide causes pellagra, a disease associated with an inadequately supplemented maize diet. Nicotinic acid (niacin) and its amide are... 

A reversible covalent modification that plants use extensively is the reduction of cystine disulfide bridges to sulf-hydryls. Many of the enzymes of photosynthetic carbohydrate synthesis are activated in this way (table 9.3). Some of the enzymes of carbohydrate breakdown are inactivated by the same mechanism. The reductant is a small protein called thioredoxin, which undergoes a complementary oxidation of cysteine residues to cystine (fig. 9.5). Thioredoxin itself is reduced by electron-transfer reactions driven by sunlight, which serves as a signal to switch carbohydrate metabolism from carbohydrate breakdown to synthesis. In one of the regulated enzymes, phosphoribulokinase, one of the freed cysteines probably forms part of the catalytic active site. In nicotinamide-adenine dinucleotide phosphate (NADP)-malate dehydrogenase and fructose-1,6-bis-... 

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. 

There are two other cofactors that can participate in redox processes these are /lavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide phosphate (NADP+). both of which are shown in Fig. 11-2. FAD accepts 2H s and is thereby reduced to FADH2, whereas NADP+ accepts H and is reduced to NADPH and H +. Both of these reduced cofactors can be oxidized, thereby donating their H s (or reducing equivalents), similar to the oxidation of NADH. The enzymes that catalyze those reactions involving an oxidation or a reduction are usually very selective toward a particular cofactor (NAD or NADP) in a particular oxidation state. 

The vast majority of alcohol dehydrogenases require nicotanimide cofactors, such as nicotinamide adenine dinucleotide (NADH) and its respective phosphate NADPH. The structure of NAD/NADP is shown in Fig. 3.39. Hydrogen and two electrons are transferred from the reduced nicotinamide to the carbonyl group to effect a reduction of the substrate (see Fig. 3.39). 

Photosynthesis comprises a light-induced and a dark reaction. The first, called photophosphorylation, involves the two-electron reduction of nicotinamide adenine dinucleotide phosphate (NADP+) by water, to produce NADPH and oxygen. The redox reaction is coupled to the generation of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) ... 

Niacin is a water-soluble vitamin. The RDA of niacin for the adult man is 19 mg. Niacin is converted in the bi>dy to the cofactor nicotinamide adenine dinucleotide (NAD). NAD also exists in a phosphorylated form, NADP The phosphate group occurs on the 2-hydrr>xyl group of the AMP half of the coenzyme, NAD and NADP are used in the catalysis of oxidation and reduction reactions. These reactions are called redox reactions. NAD cycles between the oxidized form, NAD, and the reduced form, NADH + H. The coenzyme functions to accept and donate electrons. NADP behaves in a similar fashion. It occurs as NADP and NADPH + HT The utilization of NAD is illustrated in the sections on glycolysis, the malatc-aspartate shuttle, ketone body metabolism, and fatty acid oxidation. The utilization of NADP is illustrated in the sectirrns concerning fatty acid synthesis and the pentose phosphate pathway. 

Hydrogen resulting from the photolysis of water to be used eventually for the reduction of CO2 is first bound to the coenzyme nicotinamide adenine dinucleotide phosphate (NADP). 

The electrochemical reduction of pyridinium cations and other positively charged A-het-eroaromatic systems has received considerable attention as models for nicotinamide adenine dinucleotide (NAD" ) and nicotinamide adenine dinucleotide phosphate (NADP ). 

In vivo, most electrons from reduced ferredoxin are passed onto nicotinamide adenine dinucleotide phosphate cation (NADP ), via ferredoxin-NADP reductase, to generate the NADPH needed to drive carbon dioxide fixation by the Calvin cycle. Thus electrons from photosystem I can pass through at least three routes (Figure 1), of which route C is preferred (II). However, if the supply of NADP were limited, for example, because of a poor supply of carbon dioxide causing a slow turnover of the Calvin cycle, the electron flow rate along pathway C would be expected to be decreased and more 02" should be made by route B and, to a lesser extent, by route A (15-17), Some oxygen reduction takes place even when carbon dioxide is present in ample amounts (18). 

Fig. 1.5 Nicotinamide adenine dinucleotide (NAD+) and its phosphorylated analog (NADP+). The difference is indicated in purple. NAD+ and NADP+ undergo reduction to NADH and NADPH by accepting a hydride ion and two electrons and releasing a proton from an oxidized substrate. (Adapted from Fig. 14-13 in Berg JM, Tymoczko JL and Stryer L. Biochemistry, 5th Ed. 2002. W.H. Freeman Co., New York)...

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