Transitioning enzyme catalysis towards photocatalysis.

Enzyme biocatalysis is being industrialized at a phenomenal rate. Biocatalysis offers routes to chemical transformations that avoid the use of expensive metal catalysts, high temperatures and pressures, while providing impressive enantio-, regio- and chemo-selectivities. Working individually or as cascades, in live cells or cell-free preparations, to manufacture everyday chemicals, materials, healthcare products, fuels and pharmaceuticals and in diagnostic and industrial sensing applications, enzymes are key enablers in a circular bioeconomy. An ability to exploit and tailor biocatalysts rapidly and predictably requires knowledge of structure-mechanism relationships and the physical chemistry of enzyme action. This knowledge has advanced since our millennium article on this topic (Sutcliffe and Scrutton . 2000. 358, 367-386). Here, we discuss an emerging frontier-enzyme photobiocatalysis. Photoenzymes are rarely found in nature. This limits 'difficult-to-achieve' reactions in biology that are generally accessible to chemical photocatalysts. We discuss here the emergence of photobiocatalysis as a new frontier. We review knowledge of natural photoenzymes and identify challenges and limitations in their use as photobiocatalysts. We consider emerging reports on repurposing natural enzymes as photobiocatalysts. We also discuss prospects for de novo design of photobiocatalysts which as a general concept would transform catalysis science.This article is part of the theme issue 'Science into the next millennium: 25 years on'.