Nicotinamide adenine dinucleotide hydride NADH/NADPH

Nicotinamide adenine dinucleotide hydride (NADH) Metabolite that can carry electron pairs to different places in the cell. These pairs can be used for building chemical bonds or burning (respiration for energy by combination with oxygen). Most cells also use a second functionally identical form with an added phosphate called NADPH. 

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... 

Zinc-containing alcohol dehydrogenases take up two electrons and a proton from alcohols in the form of a hydride. The hydride acceptor is usually NAD(P) (the oxidized form of nicotinamide adenine dinucleotide (NADH) or its phosphorylated derivative, NADPH). Several liver alcohol dehydrogenases have been structurally characterized, and Pig. 17.8 shows the environment around the catalytic Zn center and the bound NADH cofactor. 

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-... 

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)...

Bacteria use two redox carriers nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH). The abbreviations in the parentheses denote the carriers when they are in the reduced form. When these molecules are in their oxidized forms (NAD+, NADP ), they abstract electrons from molecules in the form of a hydride and in the process, become reduced (NADH, NADPH). For example, the reaction A + NAD+ —> B + NADH occurs where B is more oxidized than A, and the electrons are transferred by adding a hydride to NAD to yield the reduced cofactor, NADH. 

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