Bioelectrocatalyzed Synthesis by Wired Enzyme Assemblies

The coupling of enzymatic and electrochemical reactions has provided efficient tools, not only for analytical but also for synthetic purposes. In the latter field, the possibilities of enzymatic electrocatalysis, for example, the coupling of glucose oxidation (catalyzed either by GOx or GDH) to the electrochemical regeneration of a co-substrate (benzoquinone or NAD+) have been demonstrated [362-364]. An electroenzymatic reactor has also been developed [363-364] to demonstrate the production of biochemicals on a laboratory scale. NAD(P)+ derivatives immobilized by covalent attachment to polymer matrices or protein backbones have been used in enzyme reactors [365, 366]. Another important coenzyme ubiquinone can be regenerated at an electrode [367, 371] and applied to drive secondary enzymatic reactions with the participation of membrane enzymes (e.g. fumarate reductase). 

A biosynthetic multienzyme reaction of particular interest involves carbon dioxide fixation with the production of methanol [373, 374]. FDH catalyzes the reduction of carbon dioxide to formate, and methanol dehydrogenase (M DH) catalyzes the reduction of formate to methanol. Both of these enzymes require NAD+/NADH-cofactor, and in the presence of the reduced dimethyl viologen mediator (MV +), they can drive a sequence of enzymatic reactions. The cascade of biocatalytic reactions results in the reduction of GO2 to formate catalyzed by FDH, followed by the reduction of formate to methanol catalyzed by MDH. A more complex system composed of immobilized cells of Parococcus deni-trijicans has been demonstrated for the reduction of nitrate and nitrite [375]. 

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