Nicotinamide adenine dinucleotide phosphate hydride NADPH

NADPH nicotinamide adenine dinucleotide phosphate hydride... 

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... 

DHFR catalyses the hydride-ion transfer between the nicotinamide adenine dinucleotide phosphate (NADPH) cofactor and a substrate molecule (S) according to... 

DHFR catalyzes the reduction of 7,8-dihydrofolate (H2F) to 5,6,7,8-tetrahydrofolate (H4F) using nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor (Fig. 17.1). Specifically, the pro-R hydride of NADPH is transferred stereospecifi-cally to the C6 of the pterin nucleus with concurrent protonation at the N5 position [1]. Structural studies of DHFR bound with substrates or substrate analogs have revealed the location and orientation of H2F, NADPH and the mechanistically important side chains [2]. Proper alignment of H2F and NADPH is crucial in enhancing the rate of the chemical step (hydride transfer). Ab initio, mixed quantum mechanical/molecular mechanical (QM/MM), and molecular dynamics computational studies have modeled the hydride transfer process and have deduced optimal geometries for the reaction [3-6]. The optimal C-C distance between the C4 of NADPH and C6 of H2F was calculated to be 2.7A [5, 6], which is significantly smaller than the initial distance of 3.34 A inferred from X-ray crystallography [2]. One proposed chemical mechanism involves a keto-enol tautomerization (Fig. 

This reaction fixes carbon but there is no net change in oxidation number. The CO2 is reduced to carboxyl but one of the carbon atoms in the RuBP is oxidized to yield the second carboxyl group. In subsequent steps, each mole of PGA reacts with a mole of NADPH in order to produce two moles of 3-phosphoglyceraldehyde, a product in which average oxidation number of carbon is 0. NADPH is the reduced form of nicotinamide adenine dinucleotide phosphate (see any biochemistry text for structures and further details). In biosynthetic processes, it functions as a hydride donor or reductant. A typical reaction is shown below. Note that NADPH + H is equivalent to NADP + H2. 

Hydride transfer from NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate) gives initially mevaldyl-CoA which then forms mevaldehyde. Another reduction with NADPH gives mevalonate. 

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. 

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. 

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