Methods for the regeneration of nicotinamide coenzymes

Oxidoreductase is the largest class of enzymes and has broad applications in biotechnology since a number of bioconversions involve oxidation/reduction reactions. Coenzymes are always required in oxidoreductase-catalyzed reactions, where nicotinamide coenzymes, NAD(P)H/NAD(P)+, are the most commonly used. They undergo reactions with substrates in biocatalytic processes by converting into their reductive or oxidative forms. The efficient and economical regeneration of nicotinamide coenzymes is therefore of particular significance for industrial applications due to their high cost and large usage. The principal methods used for the regeneration of nicotinamide coenzymes, including enzymatic, chemical, electrochemical and photochemical regeneration methods are surveyed with emphasis on the crucial issues and the state-of-art research relevant to each method. Screening and improving the performance of the enzymes, designing and implementing efficient regeneration routes as well as retaining/recycling coenzymes are the three key issues for the enzymatic method. Development of efficient catalysts with high selectivity is the top priority of the chemical regeneration method. For the electrochemical regeneration method, improvement of the electrode by modification of either the nano-materials or electron mediators is the major concern. The focus of the photochemical regeneration method lies in the exploitation of efficient visible-light photosensitizers.