Catalytic Promiscuity of Horseradish Peroxidase: Aerobic Oxidative Regeneration of Oxidized Nicotinamide Cofactors

NAD(P)+ regeneration is of great importance for dehydrogenase (DH)‐catalyzed oxidations. In this work, we report horseradish peroxidase (HRP)‐catalyzed aerobic oxidation of the reduced nicotinamide cofactors, including natural and non‐natural ones, into the oxidized form at neutral and alkaline pH enabled by external amino acids (AAs). HRP showed promiscuous yet extremely low oxidase activity toward NADH at pH 7 in the absence of both AAs and mediators, as evidenced by the observation of compound III. The mechanistic study revealed that AAs as decoy molecules (likely act as acid‐base catalysts) and mediators significantly promoted the formation of compound III as well as its decay back to the ground state. The applicability of the aerobic cofactor regeneration method was demonstrated by the HRP total turnover number up to 88 000 as well as high yields (91–99 %) in bi‐enzymatic synthesis of carboxylic acids. The present work offers an alternative method to recycle NAD(P)+. Also, it may open up possibilities for HRP‐catalyzed aerobic oxidations. A novel enzymatic aerobic oxidative regeneration method for NAD(P)+ was developed, based on the promiscuous oxidase activity of horseradish peroxidase.