Coupling of the Catalytic Reactions of Formate Dehydrogenase and Hydrogenase in Solution: Insights from in situ IR Spectroscopy and Computations.

Sophisticated enzymatic systems have evolved in nature to efficiently couple distinct biochemical reactions in form of cascades. As such, they serve as reference models to understand the indirect interactions of catalytic centers. Herein, we studied, in solution, the coupling of the reactions from membrane‐bound [NiFe] hydrogenase (MBH) from <italic>Cupriavidus necator</italic> (reversible H2 splitting into H+ and e−) and the molybdenum‐dependent formate dehydrogenase from <italic>Rhodobacter capsulatus</italic> (reversible formate to CO2 interconversion). To follow their interplay via the characteristic absorptions from the MBH's active site or the respective substrate and product bands of FDH, we utilized in situ IR spectrocopy and GC(‐MS), in the absence and presence of soluble redox mediators. Coarse‐grained molecular dynamics (CGMD) computations revealed the lack of productive enzyme complexes for direct electron transfer (ET). Thus, the observed minor amounts of H2 or formate were produced from transient interactions between the two enzymes. On the contrary, the significantly increased product formation in the presence of methyl viologen can be related to the putative multiple interaction sites of the redox mediator with FDH identified by CGMD. Our study represents a proof‐of‐concept approach that can be used in the future to develop novel coupled biocatalytic systems by identifying potential ET pathways. [ABSTRACT FROM AUTHOR]