The recent increase of interest in photocatalysis spread to biocatalysis and triggered a rush for the development of light-dependent enzyme-mediated or enzyme-coupled processes. After several years of intense research on photobiocatalysis, it is time to evaluate the state of the field in a structured manner. In this Perspective, we suggest to group photobiocatalysis into distinct disciplines and provide principal guidelines and standards for the reporting of photobiocatalytic research results as well as advice on performing photobiocatalytic reactions. Overall, we assess that the field contributes to the diversity of biocatalytic reactions while offering the selectivity of enzymes to photocatalysis. We foresee that the ongoing excitement for light-dependent enzymatic processes will lead to the discovery of novel photobiocatalytic mechanisms to complement biocatalysis with new bond-forming reactions and will provide additional innovative strategies to utilize light as a possible benign energy source.@en

Biocatalytic asymmetric reduction of C=C and C=O bonds is highly attractive to produce valuable (chiral) chemicals for the fine and pharmaceutical industry, yet occurs at the expense of reduced nicotinamide adenine dinucleotide coenzyme NADPH that requires recycling. Established methods each have their challenges. Here we developed a light-driven approach based on photosystem I (PSI) by mimicking the natural electron transfer from PSI via ferredoxin (Fd) towards ferredoxin NADP+ reductase (FNR) in vitro. Illumination with red light led to reduction of NADP+ to NADPH with a turnover frequency of 2.55 s−1 (>9000 h−1) at pH 7.5. Light-driven NADPH regeneration by PSI-Fd-FNR was coupled with three oxidoreductases for asymmetric reduction of C=C and C=O bonds, reaching up to 99 % conversion with a turnover number of 3035, and retaining enantioselectivity. This study demonstrates the capacity of a PSI system to drive continuous NADPH-dependent biocatalytic conversions with light.@en

A recombinant enoate reductase was expressed in cyanobacteria and used for the light-catalyzed, enantioselective reduction of C=C bonds. The coupling of oxidoreductases to natural photosynthesis allows asymmetric syntheses fueled by the oxidation of water. Bypassing the addition of sacrificial cosubstrates as electron donors significantly improves the atom efficiency and avoids the formation of undesired side products. Crucial factors for product formation are the availability of NADPH and the amount of active enzyme in the cells. The efficiency of the reaction is comparable to typical whole-cell biotransformations in E. coli. Under optimized conditions, a solution of 100 mg prochiral 2-methylmaleimide was reduced to optically pure 2-methylsuccinimide (99 % ee, 80 % yield of isolated product). High product yields and excellent optical purities demonstrate the synthetic usefulness of light-catalyzed whole-cell biotransformations using recombinant cyanobacteria.@en