Nicotinamide adenine dinucleotide cosubstrate

All NOS isoforms utilize L-arginine as the substrate, and molecular oxygen and reduced nicotinamide adenine dinucleotide phosphate (NADPH) as cosubstrates. Flavin adenine dinucleotide (FMN), flavin mononucleotide (FAD), and (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) are cofactors of the enzyme. All NOS isoforms contain heme and bind calmodulin. In nNOS and eNOS,... 

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 addition to the substrate being acted on, many enzymes require a second cosubstrate. Such a cosubstrate may activate many enzymes and is an example of a cofactor or coenzyme (described previously). An example is nicotinamide adenine dinucleotide (NAD ), which is a cofactor for many dehydrogenase reactions by acting as a hydrogen acceptor ... 

Cosubstrates are loosely bound coenzymes that are reqnired in stoichiometric amonnts by enzymes. The molecnle nicotinamide adenine dinucleotide (NAD) acts as a cosubstrate in the oxidation-rednction reaction that is catalyzed by malate dehydrogenase, one of the enzymes of the citric acid cycle. 

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... 

Reoxidation of the cosubstrate at an appropriate electrode surface will lead to the generation of a current that is proportional to the concentration of the substrate, hence the coenzyme can be used as a kind of mediator. The formal potential of the NADH/NAD couple is - 560 mV vs. SCE (KCl-saturated calomel electrode) at pH 7, but for the oxidation of reduced nicotinamide adenine dinucleotide (NADH) at unmodified platinum electrodes potentials >750 mV vs. SCE have to be applied [142] and on carbon electrodes potentials of 550-700 mV vs. SCE [143]. Under these conditions the oxidation proceeds via radical intermediates facilitating dimerization of the coenzyme and forming side-products. In the anodic oxidation of NADH the initial step is an irreversible heterogeneous electron transfer. The resulting cation radical NADH + looses a proton in a first-order reaction to form the neutral radical NAD, which may participate in a second electron transfer (ECE mechanism) or may react with NADH (disproportionation) to yield NAD [144]. The irreversibility of the first electron transfer seems to be the reason for the high overpotential required in comparison with the enzymatically determined oxidation potential. 

Aicotinic acid derivatives Nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP-) (D 16.2) Coenzymes and cosubstrates of oxido-reductases (C 2.1), in humans synthesized from nicotinic acid and nicotinamide. Both substances belong to the vitamin B complex... 

In the solvent-producing clostridia, 3-hydroxybutyryl-CoA dehydrogenase (P-hydroxybutyr)d-CoA dehydrogenase enzyme 5) catalyzes the reduction of acetoacetyl-CoA to 3-hydroxybutyryl-CoA. The enzyme has been purified from C. beijerinckii NRRL B593, and it has subunit and native MWs of 30.8 and 213 kDa, respectively (Colby and Chen 1992). The enzyme can use either reduced nicotinamide adenine dinucleotide (NADH) or NADPH as a cosubstrate, but NADH gives a 60-fold higher catalytic efficiency and is likely the physiological cosubstrate. 

Typically dissociable coenzymes might better be called cosubstrates." They assume the role of a hydrogen or group donor e.g., ATP contributes a phosphate radical in the hexokinase reaction (Chapt. V-5, diagram), and nicotinamide-adenine dinucleotide (formerly coenzyme I or DPN) accepts hydrogen from the substrate. Each substance functions therefore as a second substrate, which reacts with the real substrate itself strictly stoichiometrically i.e., mole per mole and... 

Over 250 oxidoreductases (dehydrogenases) use the cosubstrate yS-nicotinamide adenine (phosphate) dinucleotide (NAD(P) ) to oxidize a substrate SHj with concomitant reduction of the cofactor to NAD(P)H. In the most cases the cofactor is bound simultaneously with the substrate in the active site of the enzyme, allowing transfer of a hydride ion from the substrate to NAD(P)-. ... 

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