Light has received increased attention for various chemical reactions but also in combination with biocatalytic reactions. Because currently only a few enzymatic reactions are known, which per se require light, most transformations involving light and a biocatalyst exploit light either for providing the cosubstrate or cofactor in an appropriate redox state for the biotransformation. In selected cases, a promiscuous activity of known enzymes in the presence of light could be induced. In other approaches, light-induced chemical reactions have been combined with a biocatalytic step, or light-induced biocatalytic reactions were combined with chemical reactions in a linear cascade. Finally, enzymes with a light switchable moiety have been investigated to turn off/on or tune the actual reaction. This Review gives an overview of the various approaches for using light in biocatalysis.

Photobiocatalysis is an alternative approach in synthesis that has received much attention in the recent years. Due to the youth of the topic, only few reactor systems are commercially available. To allow a parallel parameter‐screening approach as often used in the optimization of biocatalytic processes, a photoreactor was developed that can illuminate up to 24 samples at well‐defined reaction conditions. The device‘s optical features and temperature regulation have been thoroughly characterized and its application was demonstrated in four examples, specifically three photobiocatalytic and one photocatalytic process: (i) Light‐dependent decarboxylation using a photodecarboxylase; (ii) Reduction of protochlorophyllide using a protochlorophyllide oxidoreductase; (iii) Photosynthetic oxygen production performed by cyanobacteria; and (iv) (−)‐Riboflavin‐catalyzed (E/Z)‐isomerization of cinnamic acid derivatives.

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The recent increase of interest in photocatalysis spread to biocatalysis and triggered a rush for the development of lightdependent 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. Over-all, 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.

Many biocatalytic redox reactions depend on the cofactor NAD(P)H, which may be provided by dedicated recycling systems. Exploiting light and water for NADPH-regeneration as it is performed, e.g. by cyanobacteria, is conceptually very appealing due to its high atom economy. However, the current use of cyanobacteria is limited, e.g. by challenging and timeconsuming heterologous enzyme expression in cyanobacteria as well as limitations of substrate or product transport through the cell wall. Here we establish a transmembrane electron shuttling system propelled by the cyanobacterial photosynthesis to drive extracellular NAD(P)H-dependent redox reactions. The modular photo-electron shuttling (MPS) overcomes the need for cloning and problems associated with enzyme-or substrate-toxicity and substrate uptake. The MPS was demonstrated on four classes of enzymes with 19 enzymes and various types of substrates, reaching conversions of up to 99 % and giving products with > 99 % optical purity.

Many aldehydes are volatile compounds with distinct and characteristic olfactory properties. The aldehydic functional group is reactive and, as such, an invaluable chemical multi‐tool to make all sorts of products. Owing to the reactivity, the selective synthesis of aldehydic is a challenging task. Nature has evolved a number of enzymatic reactions to produce aldehydes, and this review provides an overview of aldehyde‐forming reactions in biological systems and beyond. Whereas some of these biotransformations are still in their infancy in terms of synthetic applicability, others are developed to an extent that allows their implementation as industrial biocatalysts.

Many biocatalytic redox reactions depend on the cofactor NAD(P)H, which may be provided by dedicated recycling systems. Exploiting light and water for NADPH‐regeneration as it is performed, e.g. by cyanobacteria, is conceptually very appealing due to its high atom economy. However, the current use of cyanobacteria is limited, e.g. by challenging and time‐consuming heterologous enzyme expression in cyanobacteria as well as limitations of substrate or product transport through the cell wall. Here we establish a transmembrane electron shuttling system propelled by the cyanobacterial photosynthesis to drive extracellular NAD(P)H‐dependent redox reactions. The modular photo‐electron shuttling (MPS) overcomes the need for cloning and problems associated with enzyme‐ or substrate‐toxicity and substrate uptake. The MPS was demonstrated on four classes of enzymes with 19 enzymes and various types of substrates, reaching conversions of up to 99 % and giving products with >99 % optical purity.