Enzymes cofactor-dependent

A number of mechanistically distinct enzymes can likewise be employed for the synthesis of product structures identical to those accessible from aldolase catalysis. Such alternative cofactor-dependent enzymes (e.g. transketolase) are emerging as useful catalysts in organic synthesis. As these operations often extend and/or... 

The use of water-miscible organic solvent-water mixtures is a particularly attractive method for use with cofactor-dependent enzymes due to its simphcity. The high water content can allow dissolution of both enzyme and cofactor, whilst the water-miscible solvent can provide a dual role in both substrate dissolution and as a cosubstrate for cofactor recycling (substrate-coupled cofactor recycling).The asymmetric reduction of a ketone intermediate of montelukast using an engineered ADH in the presence of 50 % v/v isopropanol offers a powerful demonstration of this methodology (Scheme 1.55). 

Multi-layer enzyme sensors offer the opportunity to separate the signals of different analytes. For this purpose a cofactor dependent enzyme converting the analyte A is fixed in front of a layer which contains enzymes converting both analytes B and A under the formation of an electrode-active product. Two procedures for separating the signals for both analytes have been established. 

Application of the Bioreduction System to Other Cofactor-Dependent Enzyme Reactions Discovery of New Functions of Old Yellow Enzymes... 

Lee CY, Johansson CJ. Purification of cofactor-dependent enzymes by affinity chromatography. Analyt. Biochem. 1977 77 90-102. 

Walker AT, Bruce NC (2004) Cofactor-dependent enzyme catalysis in functionalized ionic solvents. Chem Commun 22 2570-2571... 

The glycolytic pathway includes three such reactions glucose 6-phosphate isomer-ase (1,2-proton transfer), triose phosphate isomerase (1,2-proton transfer), and eno-lase (yS-elimination/dehydration). The tricarboxylic acid cycle includes four citrate synthase (Claisen condensation), aconitase (j5-elimination/dehydration followed by yS-addition/hydration), succinate dehydrogenase (hydride transfer initiated by a-proton abstraction), and fumarase (j5-elimination/dehydration). Many more reactions are found in diverse catabolic and anabolic pathways. Some enzyme-catalyzed proton abstraction reactions are facilitated by organic cofactors, e.g., pyridoxal phosphate-dependent enzymes such as amino acid racemases and transaminases and flavin cofactor-dependent enzymes such as acyl-C-A dehydrogenases others. 

Figure 10 Overview of BH4 biosynthesis and regeneration, including cofactor-dependent metabolic pathways. BH4-metabolizing enzymes are in biue, cofactor-dependent enzymes are in red (see also text for details and abbreviations of enzymes).

Photosensitized regeneration of the biologically active NAD(P)H cofactors allows their subsequent coupling to cofactor-dependent enzymes. As a result, a series of photosynthetic transformations have been driven [78,81] using various enzymes and their respective substrates by the general scheme outlined in Figure 18. Table 2 summarizes various photosynthetic... 

A number of oxidations and reductions have been carried out in microemulsions using enzymes such as cholesterol oxidase [64,108,109], bilirubin oxidase [110], horseradish peroxidase [111,112], and horse liver alcohol dehydrogenase (HLADH) [73,112-118]. It is noteworthy that cofactor-dependent enzymes also work well in different types of microemulsions. In fact, kinetic studies on the HLDAH-NADH (NADH stands for the reduced form of nicotinamide adenine dinucleotide) system showed that the presence of coenzyme was essential for the long-term stability of the enzyme in a microemulsion [113,115]. 

The large-scale industrial exploitation of cofactor-dependent enzymes has been considered an issue for a long time due to both the increased process complexity and the cost of the coenzymes to be added to the reaction mixture when they are not covalently bound to the biocatalyst. 

Instead, the orthogonal multienzymatic reactions are always cascade processes by definition. However, this type of multienzymatic processes has been largely investigated in the past especially for the development of enzymecofactor regeneration systems. These studies not only allowed the wide exploitation of cofactor-dependent enzymes, such as NAD(P)H-dependent dehydrogenases, by making their reactions economically feasible but were also useful in identifying relevant process options for the development of effective multienzymatic reaction systems (3). 

The integration of cofactor-dependent enzymes as anodic catalysis clearly faces a number of technical hurdles that must be considered and addressed. To some extent, the stability of the NAD" /NADH couple has been addressed by introduction of electropolymerized polymers that has directly led to extended bioanode lifetimes. 

Bardea A, Katz E, Bueckmann AF, WiUner I. NAD -dependent enzyme electrodes electrical contact of cofactor-dependent enzymes and electrodes. J Am Chem Soc 1997 119 9114-9119. 

The conclusion was that fixed-bed reactors employing covalently immobilized enzymes are the most advantageous for repeated transformations because of increased enzyme stability, high coenz3nme turnover number [12], and satisfiujtory mass transfer rates. These two-phase reactors demonstrated that cofactor-dependent enzymes can be used in flow systems with no need for macromolecular coenzymes and appear to be the most suitable for scaling up. Free enzymes, which are easier to handle, are preferable for occasional use and small-scale preparations. 

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