In the field of green chemistry, light – an attractive natural agent – has received particular attention for driving biocatalytic reactions. Moreover, the implementation of light to drive (chemo)enzymatic cascade reactions opens up a golden window of opportunities. However, there are limitations to many current examples, mostly associated with incompatibility between the enzyme and the photocatalyst. Additionally, the formation of reactive radicals upon illumination and the loss of catalytic activities in the presence of required additives are common observations. As outlined in this review, the main question is how to overcome current challenges to the exploitation of light to drive (chemo)enzymatic transformations. First, we highlight general concepts in photo‐biocatalysis, then give various examples of photo‐chemoenzymatic (PCE) cascades, further summarize current synthetic examples of PCE cascades and discuss strategies to address the limitations.

In this study, we coupled a well‐established whole‐cell system based on E. coli via light‐harvesting complexes to Rieske oxygenase (RO)‐catalyzed hydroxylations in vivo. Although these enzymes represent very promising biocatalysts, their practical applicability is hampered by their dependency on NAD(P)H as well as their multicomponent nature and intrinsic instability in cell‐free systems. In order to explore the boundaries of E. coli as chassis for artificial photosynthesis, and due to the reported instability of ROs, we used these challenging enzymes as a model system. The light‐driven approach relies on light‐harvesting complexes such as eosin Y, 5(6)‐carboxyeosin, and rose bengal and sacrificial electron donors (EDTA, MOPS, and MES) that were easily taken up by the cells. The obtained product formations of up to 1.3 g L−1 and rates of up to 1.6 mm h−1 demonstrate that this is a comparable approach to typical whole‐cell transformations in E. coli. The applicability of this photocatalytic synthesis has been demonstrated and represents the first example of a photoinduced RO system.

In dieser Studie wurde ein auf E. coli basierendes Ganzzellsystem über Lichtsammelkomplexe an Rieske‐Oxygenasen(RO)‐katalysierte Hydroxylierungen in vivo angekoppelt. Obwohl diese Enzyme vielversprechende Biokatalysatoren darstellen, wird ihre praktische Anwendbarkeit durch ihre Abhängigkeit von NAD(P)H sowie ihre Mehrkomponentennatur und intrinsische Instabilität in zellfreien Systemen beeinträchtigt. Um die Grenzen von E. coli als Chassis für künstliche Photosynthese zu erforschen, sowie aufgrund der berichteten Instabilität von ROs, haben wir diese herausfordernden Enzyme als Modellsystem verwendet. Der Licht‐getriebene Ansatz beruht auf Lichtsammelkomplexen wie beispielsweise Eosin Y, 5(6)‐Carboxyeosin oder Rose Bengal und Elektronendonoren (EDTA, MOPS oder MES), die von den Zellen leicht aufgenommen werden können. Die erzielten Produktbildungen von bis zu 1.3 g L−1 und Raten von bis zu 1.6 mm h−1 zeigen, dass dies ein vergleichbarer Ansatz zu typischen Ganzzelltransformationen in E. coli ist. Die Anwendbarkeit dieser photokatalytischen Synthese wurde demonstriert und ist das erste Beispiel eines photoinduzierten RO‐Systems.

Enzymes that depend on sophisticated electron transfer via ferredoxins (Fds) exhibit outstanding catalytic capabilities, but despite decades of research, many of them are still not well understood or exploited for synthetic applications. This review aims to provide a general overview of the most important Fddependent enzymes and the electron transfer processes involved. While several examples are discussed, we focus in particular on the family of Rieske non-heme iron-dependent oxygenases (ROs). In addition to illustrating their electron transfer principles and catalytic potential, the current state of knowledge on structure-function relationships and the mode of interaction between the redox partner proteins is reviewed. Moreover, we highlight several key catalyzed transformations, but also take a deeper dive into their engineerability for biocatalytic applications. The overall findings from these case studies highlight the catalytic capabilities of these biocatalysts and could stimulate future interest in developing additional Fddependent enzyme classes for synthetic applications.