Nicotinamide adenine dinucleotide recycling

The asymmetric reduction of prochiral functional groups is an extremely useful transformation in organic synthesis. There is an important difference between isolated enzyme-catalyzed reduction reactions and whole cell-catalyzed transformations in terms of the recycling of the essential nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] cofactor. For isolated enzyme-catalyzed reductions, a cofactor recycling system must be introduced to allow the addition of only a catalytic amount (5% mol) of NAD(P)H. For whole cell-catalyzed reductions, cofactor recycling is automatically achieved by the cell, and the addition of a cofactor to the reaction system is normally not required. 

It is possible to use isolated, partially purified enzymes (dehydrogenases) for the reduction of ketones to optically active secondary alcohols. However, a different set of complications arises. The new C H bond is formed by delivery of the hydrogen atom from an enzyme cofactor, nicotinamide adenine dinucleotide (phosphate) NAD(P) in its reduced form. The cofactor is too expensive to be used in a stoichiometric quantity and must be recycled in situ. Recycling methods are relatively simple, using a sacrificial alcohol, or a second enzyme (formate dehydrogenase is popular) but the real and apparent complexity of the ensuing process (Scheme 8)[331 provides too much of a disincentive to investigation by non-experts. 

The pentose phosphate pathway (PPP) is the major pathway for recycling nicotinamide adenine dinucleotide (NAD) to nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) and for the production of ribose-5-phosphate that is needed for the synthesis of nucleotides. The function of the PPP depends on the synthesis of nicotinamide-adenine dinucleotide phosphate (NADP) and thiamin pyrophosphate, a coenzyme... 

In the energy metabolism of cells, an intermediate carrier of the electrons (and protons) is commonly required. Such an electron carrier is, for instance, NAD+ (nicotinamid adenin dinucleotide), which formally accepts two electrons and one proton and is thereby reduced to NADH. The NADH may give off the electrons again to specialized electron acceptors and the protons are released in the cell sap. Thereby, the NADH, which must be used repeatedly, is recycled. 

The xylose reductase (XR) catalyzes the first step of a fungal pathway that allows certain organisms to metabolize xylose, such as Candida boidinii [6], Candida guilliermondii [7], Candida tmpicalis [8], Candida parapsilosis [9], and Debaryomyces hansenii [10]. After the reduction of xylose to xylitol by XR in a manner that can utilize nicotinamide adenine dinucleotide (reduced form NADH) or nicotinamide adenine dinucleotide phosphate (reduced form NADPH), xylitol is re-oxidized to xylulose by xyUtol dehydrogenase, which is often specific for nicotinamide adenine dinucleotide (NAD) [11]. Xylulose is then phosphorylated. An efficient, pathway should recycle the cosubstrate such that there is no... 

Studies of the recycling of the cofactor in an enzyme reactor comparison of reactions using free or immobilized nicotinamide adenine dinucleotide Investigations of the role of carbonic anhydrases in vivo Purification of tryptophanase and tyrosine phenol-lyase... 

For this process to run, ferredoxin has to be recycled through oxidation. The recycling process is dependent on the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to ferredoxin. 

The reductive steps in fatty-acid synthesis require reduced nicotinamide adenine dinucleotide phosphate (NADPH). Some NADPH is produced during recycling of the oxaloacetate formed during the cytoplasmic hydrolysis of citrate, described above. Oxaloacetate is first converted to malate (via cytoplasmic malate dehydrogenase). Malate is then... 

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