Electrochemical regeneration of oxidoreductases for cell-free biocatalytic redox reactions

Oxidoreductases represent a highly interesting and versatile class of biocatalysts for specific reduction, oxidation, and oxyfunctionalization reactions. Since oxidoreductases depend on cofactors and coenzymes to supply or withdraw redox equivalents released during the catalytic process, their application in cell-free environments requires external supply with these redox equivalents. Next to enzymatic approaches, a variety of non-enzymatic regeneration strategies have been developed. This review focuses on electrochemical methods for the in situ regeneration of nicotinamide cofactors as well as flavin- and heme-coenzymes, developed for synthetic application. The fields of electrochemical biosensors as well as biofuel cells are not discussed in detail. Electrochemical approaches bear much promise and in some cases are more efficient and more versatile than enzymatic regeneration approaches.