Direct electrochemistry of redox enzymes as a tool for mechanistic studies.

This review regards the use of dynamic electrochemistry to study the mechanism of redox enzymes, with exclusive emphasis on the configuration where the protein is adsorbed onto an electrode and electron tranfer is direct. We still often come across the statement these days that redox enzymes are too large and too fragile to interact directly with a metallic electrode without being at least partly denatured. It is still held that since the active site of these enzymes is deeply buried in the protective protein matrix, direct electron exchange with an electrode can only occur under exceptional conditions. Yet 20 years have passed since it was shown that direct electron transfer (ET) can occur between an electrode and a large, catalytically active enzyme, and about one hundred examples have already been reported. The oxidoreductases that are most auspicious for achieving direct “wiring” interact with their soluble redox partner (cytochrome, ferredoxin, quinone, or redox dye) by an outer sphere ET which occurs at (or close to) the surface of the enzyme, where the electrode can also interact. Having redox enzymes directly connected to electrodes made it possible to exploit the naturally high efficiency of these biological systemsfordevelopingselectivethird-generationbiosensors, environmentally sound biofuel cells, heterogeneous catalysts, and even biomolecular electronic components. By combining dynamic electrochemistry and scanning probe microscopic techniques, it has now become possible to characterize the protein-electrode interface and electron exchange processes in great detail. Closer to our concerns, this configuration has recently proved useful for learning about the kinetic and molecular aspects of the catalytic mechanism of redox enzymessthis is the topic of the present review.