Fuelling Unspecific Peroxygenases with In‐Situ Generated H₂O₂ Using Enzyme Fusions

Unspecific peroxygenases (UPO) have been widely studied for different reactions as they are often considered as the dream biocatalyst. UPOs only require H 2 O 2 to perform C─H oxyfunctionalization reactions. However, excessive supply of peroxides can also lead to enzyme inactivation. Therefore, strategies to slowly supply the peroxide are being investigated. Here, we report a bifunctional biocatalyst that is comprised of a formate dehydrogenase and an azoreductase with a peptide linker in‐between. It was shown that the fusion constructs can be used as an in situ H 2 O 2 generator to fuel the unspecific peroxygenase from Collariella viriscens ( Cvi UPO). Fusion protein can also inherently produce H 2 O 2 but addition of free FMN led to 10‐fold production of peroxides. Moreover, it was found that by coupling the fusion protein with Cvi UPO, supply level and delivery of H 2 O 2 can affect C─H oxyfunctionalization reaction and even enantioselectivity. Ethylbenzene and thioanisole were used as model substrates to demonstrate the importance of H 2 O 2 delivery. Cvi UPO was not active with ethylbenzene even with just 1 mM H 2 O 2 but coupled reactions with the FDH‐AzoRo fusion showed improved activities with preferences for the R ‐enantiomer. This study demonstrates how the rate and the delivery of peroxides are crucial to enantioselective reactions.