Conclusions and Outlooks
Electrochemistry of redox enzymes is rapidly evolving, and can be employed to
construct a broadly applicable technology. Increasing attention in this area is driven
by remarkable progress in designing electrode surfaces efficient for the interfacial electron transfer between redox enzymes and electrodes, protein-engineering
of redox enzymes, and also important applications to biosensors, biofuel cells, and
bioreactors.
The concept of the coupling of specific redox enzyme reactions with non-specific
electrode reactions seems to be simple at first glance. However, deep understanding of
redox enzymes and interfacial electron transfer is absolutely necessary for improvement of the performance and application of the bioelectrocatalysis. Loose substrate
specificity of one of substrates of redox enzymes (excepting NAD(P)-dependent
dehydrogenases) is essential for the coupling. Charge transfer at electrodes is the electron transfer, while that of NAD(P)(H), sugars, organic acids, alcohols, aldehydes,
and other organic compounds is the hydride ion transfer. Flavins, quinones, and
phenothiazines intermediate between the electron and hydride ion transfers thanks
to the two-step single-electron transfer characteristics, and then can communicate
with electrodes as in the case of metal ion-based redox cofactors in redox enzymes
and metal ion-containing redox compounds.
In MET-type bioelectrocatalysis, the LFER concept is very important in the selection of mediators, since the interfacial electrode reaction is non-specific in essence.
Further development of redox polymers that can immobilize and electrochemically
communicate with redox enzymes is desired for practical applications.
Recent progress in the understanding and improvement of DET-type bioelectrocatalysis is remarkable. Since redox enzymes are huge in size compared with
metal-based catalysts, orientation effects of redox enzymes often appear on DET-type
signals. The effects are not convenient for DET-type bioelectrocatalysis. Significance
of mesoporous structures of electrodes has become known to minimize the effects,
as called curveture effect. Several modification of electrode surfaces and mutations
of redox enzymes have also been examined to control the orientation of enzymes
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7
133
Electrochemistry of redox enzymes is rapidly evolving, and can be employed to
construct a broadly applicable technology. Increasing attention in this area is driven
by remarkable progress in designing electrode surfaces efficient for the interfacial electron transfer between redox enzymes and electrodes, protein-engineering
of redox enzymes, and also important applications to biosensors, biofuel cells, and
bioreactors.
The concept of the coupling of specific redox enzyme reactions with non-specific
electrode reactions seems to be simple at first glance. However, deep understanding of
redox enzymes and interfacial electron transfer is absolutely necessary for improvement of the performance and application of the bioelectrocatalysis. Loose substrate
specificity of one of substrates of redox enzymes (excepting NAD(P)-dependent
dehydrogenases) is essential for the coupling. Charge transfer at electrodes is the electron transfer, while that of NAD(P)(H), sugars, organic acids, alcohols, aldehydes,
and other organic compounds is the hydride ion transfer. Flavins, quinones, and
phenothiazines intermediate between the electron and hydride ion transfers thanks
to the two-step single-electron transfer characteristics, and then can communicate
with electrodes as in the case of metal ion-based redox cofactors in redox enzymes
and metal ion-containing redox compounds.
In MET-type bioelectrocatalysis, the LFER concept is very important in the selection of mediators, since the interfacial electrode reaction is non-specific in essence.
Further development of redox polymers that can immobilize and electrochemically
communicate with redox enzymes is desired for practical applications.
Recent progress in the understanding and improvement of DET-type bioelectrocatalysis is remarkable. Since redox enzymes are huge in size compared with
metal-based catalysts, orientation effects of redox enzymes often appear on DET-type
signals. The effects are not convenient for DET-type bioelectrocatalysis. Significance
of mesoporous structures of electrodes has become known to minimize the effects,
as called curveture effect. Several modification of electrode surfaces and mutations
of redox enzymes have also been examined to control the orientation of enzymes
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7
133