Cofactors dinucleotide

The biological importance of these compounds stems from their use as cofactors. Both nicotinamide and nicotinic acid ate building blocks for coen2yme I (Co I), nicotinarnide—adenine dinucleotide (NAE)) (3) and coen2yme II (Co II), nicotinarnide—adenine dinucleotide phosphate (NAE)P) (4) (2). 

Although the stmctures of ribavirin and selenazofutin are similar, they appear to exert their antiviral action at different enzyme sites along the same biochemical pathway. Selenazofutin forms the nicotinamide adenosiae dinucleotide (NAD) analogue, which inhibits IMP dehydrogenase by binding ia place of the NAD cofactor, and hence this potent reduction of guanylate pools is responsible for the antiviral effect of selenazofutin. 

In oiological systems, the most frequent mechanism of oxidation is the remov of hydrogen, and conversely, the addition of hydrogen is the common method of reduc tion. Nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP) are two coenzymes that assist in oxidation and reduction. These cofactors can shuttle between biochemical reac tions so that one drives another, or their oxidation can be coupled to the formation of ATP. However, stepwise release or consumption of energy requires driving forces and losses at each step such that overall efficiency suffers. 

The primary purification of the enzyme G3PDH was exploited herein as a preliminary study to investigate and demonstrate the feasibility of the integrated operation of cell disruption by bead milling and immediate product capture by fluidised bed adsorption (panel A in Figure 17.6). Yeast G3PDH binds nicotinamide adenine dinucleotide (NAD) as a cofactor,... 

Flavin Adenine Dinucleotide (FAD) (C27 H33 N9 O15P2) is a coenzyme that acts as a hydrogen acceptor in dehydrogenation reactions in an oxidized or reduced form. FAD is one of the primary cofactors in biological redox reactions. 

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,... 

Ethanol Electrodes The reliable sensing of ethanol is of great significance in various disciplines. The enzymatic reaction of ethanol with the cofactor nicotinamide-adenine dinucleotide (NAD+), in the presence of alcohol dehydrogenase (ADH)... 

The molyhdopterin cofactor, as found in different enzymes, may be present either as the nucleoside monophosphate or in the dinucleotide form. In some cases the molybdenum atom binds one single cofactor molecule, while in others, two pterin cofactors coordinate the metal. Molyhdopterin cytosine dinucleotide (MCD) is found in AORs from sulfate reducers, and molyhdopterin adenine dinucleotide and molyb-dopterin hypoxanthine dinucleotide were reported for other enzymes (205). The first structural evidence for binding of the dithiolene group of the pterin tricyclic system to molybdenum was shown for the AOR from Pyrococcus furiosus and D. gigas (199). In the latter, one molyb-dopterin cytosine dinucleotide (MCD) is used for molybdenum ligation. Two molecules of MGD are present in the formate dehydrogenase and nitrate reductase. 

The aldehyde oxidoreductase from Desulfovibrio gigas shows 52% sequence identity with xanthine oxidase (199, 212) and is, so far, the single representative of the xanthine oxidase family. The 3D structure of MOP was analyzed at 1.8 A resolution in several states oxidized, reduced, desulfo and sulfo forms, and alcohol-bound (200), which has allowed more precise definition of the metal coordination site and contributed to the understanding of its role in catalysis. The overall structure, composed of a single polypeptide of 907 amino acid residues, is organized into four domains two N-terminus smaller domains, which bind the two types of [2Fe-2S] centers and two much larger domains, which harbor the molybdopterin cofactor, deeply buried in the molecule (Fig. 10). The pterin cofactor is present as a cytosine dinucleotide (MCD) and is 15 A away from the molecular surface,... 

Flavoprotein enzymes contain flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD) as prosthetic groups. FMN and FAD are formed in the body from the vitamin riboflavin (Chapter 45). FMN and FAD are usually tighdy—but not covalendy—bound to their respecdve apoenzyme proteins. Metalloflavopro-teins contain one or more metals as essential cofactors. 

Four of the B vitamins are essential in the citric acid cycle and therefore in energy-yielding metabolism (1) riboflavin, in the form of flavin adenine dinucleotide (FAD), a cofactor in the a-ketoglutarate dehydrogenase complex and in succinate dehydrogenase (2) niacin, in the form of nicotinamide adenine dinucleotide (NAD),... 

For the majority of redox enzymes, nicotinamide adenine dinucleotide [NAD(H)j and its respective phosphate [NADP(H)] are required. These cofactors are prohibitively expensive if used in stoichiometric amounts. Since it is only the oxidation state of the cofactor that changes during the reaction, it may be regenerated in situ by using a second redox reaction to allow it to re-enter the reaction cycle. Usually in the heterotrophic organism-catalyzed reduction, formate, glucose, and simple alcohols such as ethanol and 2-propanol are used to transform the... 

The degradation of isoquinoline by Pseudomonas diminuta strain 7 is initiated by an oxidoreductase that contains [2Fe-2S] centers and the cofactor molybdopterin cytosine dinucleotide (Lehmann et al. 1994). 

They have a molecular mass of 300-360 kDa, and contain per molecule, eight atoms of Fe, eight atoms of acid-labile S, two atoms of Mo, and two molecules of FAD. The organic component of the pterin molybdenum cofactor is generally molybdopterin cytosine dinucleotide (Hetterich et al. 1991 Schach et al. 1995). 

Many dehydrogenase enzymes catalyze oxidation/reduction reactions with the aid of nicotinamide cofactors. The electrochemical oxidation of nicotinamide adeniiw dinucleotide, NADH, has been studied in depthThe direct oxidation of NADH has been used to determine concentration of ethanol i s-isv, i62) lactate 157,160,162,163) pyTuvate 1 ), glucose-6-phosphate lactate dehydrogenase 159,161) alanine The direct oxidation often entails such complications as electrode surface pretreatment, interferences due to electrode operation at very positive potentials, and electrode fouling due to adsorption. Subsequent reaction of the NADH with peroxidase allows quantitation via the well established Clark electrode. 

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. 

Under conditions of copper deficiency, some methanotrophs can express a cytosolic, soluble form of MMO (sMMO) (20-23), the properties of which form the focus of the present review. The sMMO system comprises three separate protein components which have all been purified to homogeneity (24,25). The hydroxylase component, a 251 kD protein, contains two copies each of three subunits in an a 82y2 configuration. The a subunit of the hydroxylase houses the dinuclear iron center (26) responsible for dioxygen activation and for substrate hydroxylation (27). The 38.6 kD reductase contains flavin adenine dinucleotide (FAD) and Fe2S2 cofactors (28), which enable it to relay electrons from reduced nicotinamide adenine dinucleotide (NADH) to the diiron center in the... 

The most important product of the hexose monophosphate pathway is reduced nicotinamide-adenine dinucleotide phosphate (NADPH). Another important function of this pathway is to provide ribose for nucleic acid synthesis. In the red blood cell, NADPH is a major reducing agent and serves as a cofactor in the reduction of oxidized glutathione, thereby protecting the cell against oxidative attack. In the syndromes associated with dysfunction of the hexose monophosphate pathway and glutathione metabolism and synthesis, oxidative denaturation of hemoglobin is the major contributor to the hemolytic process. 

In the processes that require regeneration of cofactors such as nicotinamide adenine dinucleotide phosphate (NAD(P)H) and adenosine triphosphate (ATP), whole-cell biotransformations are more advantageous than enzymatic systems [12,15]. Whole cells also have a competitive edge over the isolated enzymes in complex conversions involving multiple enzymatic reactions [14]. 

A number of molybdenum-containing hydroxylases catalyzing the first hydrox-ylation step of N-containing compounds have been characterized thoroughly (e.g., carbazole [314], quinoline [327], and indole [350]). The enzyme s redox-active has been described as a molybdenum ion site coordinated to a distinct pyranopterin cofactor (two different [2Fe2S] centers) and in most cases, flavin adenine dinucleotide centers. This active center transfers electrons from the N-heterocyclic substrate to an electron acceptor, which for many molybdenum hydroxylases is still unknown [350],... 

In the first family, the metal is coordinated by one molecule of the pterin cofactor, while in the second, it is coordinated to two pterin molecules (both in the guanine dinucleotide form, with the two dinucleotides extending from the active site in opposite directions). Some enzymes also contain FejSj clusters (one or more), which do not seem to be directly linked to the Mo centers. The molybdenum hydroxylases invariably possess redox-active sites in addition to the molybdenum center and are found with two basic types of polypeptide architecture. The enzymes metabolizing quinoline-related compounds, and derivatives of nicotinic acid form a separate groups, in which each of the redox active centers are found in separate subunits. Those enzymes possessing flavin subunits are organized as a2jS2A2, with a pair of 2Fe-2S centers in the (3 subunit, the flavin in the (3 subunit, and the molybdenum in the y subunit. 

The prodrug isoniazid (34) targets M. tuberculosis InhA [3] after activation by a mycobacterial catalase-peroxidase by reacting irreversibly with the cofactor nicotinamide adenine dinucleotide (NAD). This covalent adduct... 

Reliable measurements of L-lactate are of great interest in clinical chemistry, the dairy and vine industry, biotechnology, or sport medicine. In particular, blood lactate levels are indicative of various pathological states, including shock, respiratory insufficiencies, and heart and liver diseases. Silica sol-gel encapsulation of the lactate dehydrogenase and its cofactor was employed as a disposable sensor for L-lactate51. The sensor utilized the changes in absorbance or fluorescence from reduced cofactor nicotinamide adenine dinucleotide (NADH) upon exposure to L-lactate. 

Dehydrogenases, which represent a majority of redox enzymes, are mostly NAD (Nicotinamide Adenine Dinucleotide, see Fig. 12.9) dependent. This cofactor is not directly bound to the enzyme but its presence in the medium is necessary because it acts as a carrier of two electrons and one proton, and it activates the biocatalytic function of the enzyme. 

Since long retention times are often applied in the anaerobic phase of the SBR, it can be concluded that reduction of many azo dyes is a relatively a slow process. Reactor studies indicate that, however, by using redox mediators, which are compounds that accelerate electron transfer from a primary electron donor (co-substrate) to a terminal electron acceptor (azo dye), azo dye reduction can be increased [39,40]. By this way, higher decolorization rates can be achieved in SBRs operated with a low hydraulic retention time [41,42]. Flavin enzyme cofactors, such as flavin adenide dinucleotide, flavin adenide mononucleotide, and riboflavin, as well as several quinone compounds, such as anthraquinone-2,6-disulfonate, anthraquinone-2,6-disulfonate, and lawsone, have been found as redox mediators [43—46]. 

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