Dehydrogenases NAD+-dependent

NAD -Dependent Dehydrogenases Show Ordered Single-Displacement Mechanisms... 

Nicotinamide adenine dinucleotide (NAD )-dependent dehydrogenases are enzymes that typically behave according to the kinetic pattern just described. A general reaction of these dehydrogenases is... 

Pahnore GTR, Bertschy H, Bergens SH, Whitesides GM. 1998. A methanol/dioxygen biofuel cell that uses NAD -dependent dehydrogenases as catalysts Application of an electro-enzymatic method to regenerate nicotinamide adenine dinucleotide at low overpotentials. J Electroanal Chem 443 155-161. 

Occasionally, one can increase the Ae by utilizing alternative substrates. For example, 3-acetyl-NAD or thio-NAD can often be used with NAD -dependent dehydrogenases. Note however that an alternative substrate may change the kinetic mechanism, as compared to that observed with the naturally occurring substrate. Alternative substrates are of particular value when the normal substrate(s) and product(s) do not efficiently absorb UV or visible light. For example, many p-nitroaniline or p-nitrophenyl derivatives have proved to be quite useful in enzyme assays because they exhibit intense absorption around 410 nm. 

NAD glycohydrolases from rat liver nuclei, 66, 151 poly(ADP-ribose) synthetase from rat liver nuclei, 66, 154 poly(ADP-ribose) synthetase from calf thymus, 66, 159 extraction and quantitative determination of larger than tetrameric endogenous polyadenosine diphosphoribose from animal tissues, 66, 165 covalent modification of proteins by metabolites of NAD, 66, 168 coenzyme activity of NAD bound to polymer supports through the adenine moiety, 66, 176 use of differently immobilized nucleotides for binding NAD -dependent dehydrogenases, 66, 192. 

NAD GLYCOHYDROLASE NAD -dependent dehydrogenases, ABSORPTION SPECTROSCOPY NAD -dependent enzymes,... 

Dimethylhydrazine is metabolized by a sequence of oxidation steps, first dehydrogenation to azomethane, A -oxidation of this to azoxymethane and finally a C-oxidation to methylazoxymethanol (Fiala, 1975, 1977). This last metabolite decomposes to give the highly reactive methyldiazonium ion to which the carcinogenicity of the compound has been attributed. The sequential nature of these oxidation steps has been shown in the isolated perfused rat liver (Wolter Frank, 1982). Fiala (1977) showed that the C-oxidation of azoxymethane to methylazoxymethanol is catalysed by hepatic microsomes, while Schoental (1973) found that methylazoxymethanol was converted to the corresponding aldehyde by an NAD-dependent dehydrogenase. 

Pyridoxol (vitamin Bg). Again 1-deoxyxylulose 5-P serves as a precursor.378 In E. coli only two genes have been implicated in the condensation of this compound with 4-(phosphohydroxy)-L-threonine (Fig. 25-21, step/) 378a One is an NAD+-dependent dehydrogenase that acts on the second substrate prior to the condensation. Significant differences from the path-... 

You have isolated a tetrameric NAD+-dependent dehydrogenase. You incubate this enzyme with iodo-acetamide in the absence or presence of NADH (at 10 times the Km concentration), and you periodically remove aliquots of the enzyme for activity measurements and amino acid composition analysis. The results of the analyses are shown in the table. 

B. Leca and J.-L. Marty, Reagentless ethanol sensor based on a NAD-dependent dehydrogenase, Biosens. Bioelectron., 12(11) (1997)... 

In this case, the primary reaction is presented by the so-called citric acid cycle with the participation of various NAD+-dependent dehydrogenases synthesizing corresponding final products typical of this cycle. However, active intermediate NAD+H and H+ particles formed in the course of these reactions are able to induce reduction of aldehydes and ketones to corresponding chiral alcohols with the simultaneous regeneration of the NAD+ co-factor. 

In the primary reaction two electrons are transferred in one stage from the substrate by NAD+ in the form of hydride ion (H-) the second hydrogen atom is detached from the substrate molecule as proton (hydrogen ion H+). Note that NAD-dependent dehydrogenases participate in the citric acid cycle, carbohydrate exchange, etc. in mitochondria. 

Nearly all NAD+-dependent dehydrogenases studied follow an ordered bisubstrate mechanism. In this mechanism, the oxidation of a substrate proceeds in a sequential manner first, NAD+ binds in the active site of the dehydrogenase then the substrate binds next a hydride equivalent is transferred in a chemical step from the bound substrate to the bound NAD+, hence, oxidising the substrate and reducing the NAD+ to NADH the oxidised substrate is then released from the active site and is finally followed by the NADH. 

Acetoacetate is converted to 3-hydroxybutyrate by an NAD-dependent dehydrogenase. The reaction is reversible, and the equilibrium constant is approximately 1. 

Many assay procedures depend on the use of specific NAD-dependent dehydrogenases, e.g. ... 

Structurally, NADP differs from NAD only by a phosphate group esterified at the 2 C of the adenosine ribose, a difference which is reflected in the enzymatic roles NAD-dependent dehydrogenases are mostly involved in catabolic reactions, while NADP-specific enzymes are usually confined to biosynthetic pathways (1). The marked specificities displayed by dehydrogenases towards NAD and NADP have provided attractive model systems to understand the process of molecular recognition by protein engineering. 

A preliminary report by Obach and Van Vunakis (1990) claimed that cotinine could also be formed by a microsomal nicotinamide adenine dinucleotide (NAD) -dependent dehydrogenase (abbreviated MND). Inhibitor studies suggested that MND is not a typical aldehyde dehydrogenase. The presence of this activity in rabbit microsomes was confirmed in the authors laboratories (Flammang 1994). The rate of cotinine production from the -iminium by this route was found to be comparable to the rate of conversion of nicotine to the this enzyme might play in xenobiotic metabolism in general. It is expected that the substrate-structure dependence of MND will be quite different from that of cytosolic AO. 

Casanova-Schmitz M, Raymond MD, Heck H d A. 1984b. Oxidation of formaldehyde and acetaldehyde by NAD-dependent dehydrogenases in rat nasal mucosal homogenates. Biochem Pharmacol 33 1137-1142. 

Besides the enzymes listed in Table 1, imaging of NAD+-dependent dehydrogenase activity should be feasible. This class of more than 300 redox... 

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