Electrochemically-driven enzyme cascades: Recent developments in design, control, and modelling

The study of single redox enzymes by electrochemistry is well-established, using both mediated and direct electron exchange between the enzyme and electrode. Moving beyond single enzymes, electrochemically driven multienzyme cascades can achieve more complex transformations, and in this review, we highlight recent advances. Electrochemical control of multiple enzymes is discussed, with examples including, electrode surface modification and engineering of the enzymes to facilitate direct electron exchange with the electrode, and new developments made by the entrapment of enzymes in a highly porous electrode called the electrochemical leaf. Examples that harness the power of direct control of the potential and the ability to monitor cascade activity as electrical current, include synthesis, deracemization, and measurement of drug binding kinetics. Redox cofactors (e.g. NADP(H)) can be electrochemically regenerated by a variety of enzymes, but non-redox cofactors are less amenable to electrochemical regeneration, and we highlight enzyme cascades for adenosine triphosphate (ATP) regeneration designed with an electrochemical step to generate the required phosphate donor. Finally, we cover approaches to model electrochemically driven cascades, which predicted local environments (e.g. pH) that are difficult to measure directly and yielded guidelines for the rational design of immobilized enzyme cascade electrodes.