Direct enzymatic bioelectrocatalysis: differentiating between myth and reality

Abstract

Enzymatic bioelectrocatalysis is being increasingly exploited to better understand oxidoreductase enzymes, to develop minimalistic yet specific biosensor platforms, and to develop alternative energy conversion devices and bioelectrosynthetic devices for the production of energy and/or important chemical commodities. In some cases, these enzymes are able to electronically communicate with an appropriately designed electrode surface without the requirement of an electron mediator to shuttle electrons between the enzyme and electrode. This phenomenon has been termed direct electron transfer or direct bioelectrocatalysis. While many thorough studies have extensively investigated this fascinating feat, it is sometimes difficult to differentiate desirable enzymatic bioelectrocatalysis from electrocatalysis deriving from inactivated enzyme that may have also released its catalytic cofactor. This article will review direct bioelectrocatalysis of several oxidoreductases, with an emphasis on experiments that provide support for direct bioelectrocatalysis versus denatured enzyme or dissociated cofactor. Finally, this review will conclude with a series of proposed control experiments that could be adopted to discern successful direct electronic communication of an enzyme from its denatured counterpart.

Electrocatalytic Properties of Immobilized Heme Proteins: Basic Principles and Applications

“…[1][2][3][4][5] Redox enzymes and modified electron transfer (ET) proteins (in some cases even whole cells or biofilms) immobilized on conductive surfaces were shown to yield efficient and selective bioelectrocatalysis often with better performances than conventional electrodes. Therefore, they are excellent candidates for application in the field of electrocatalysis.…”

“…[1][2][3][4][5][6][7][8] Under these conditions, these species can yield efficient and selective bioelectrocatalysis based on direct electron transfer processes. [1][2][3][4][5][6][7][8] Under these conditions, these species can yield efficient and selective bioelectrocatalysis based on direct electron transfer processes.…”

Controlling Redox Enzyme Orientation at Planar Electrodes

“…Theoretically, using cyclic voltammetry and chronoamperometry, kinetic parameters of the catalysis can be quantified. However, the type of kinetic data which can be obtained is linked to the type of interaction between the enzyme and the electrode, and especially to the enzyme's orientation [136]. Enzyme/electrode interaction is of utmost importance because the ET rate is exponentially dependent on the distance between the redox active center and the electrochemical interface, as predicted by the Marcus theory [24,137].…”

“…This advanced analysis is mostly observed, however, on nanostructured electrodes, such as carbon nanotube-or gold nanoparticle-modified electrodes, that are able to enhance the loading of enzymes, thus increasing the detection signals. Interestingly, studying the MET/DET ratio appears to be relevant for the evaluation of the distribution of the orientation of the enzymes on the electrode [136]. In addition, being a relative value, the MET/DET ratio is free from errors caused by the variation of adsorbed enzyme amount [30].…”

Flexible and transparent biological electric power sources based on nanostructured electrodes

“…(Price and Stevens, 1982;Toone and Editor, 2007). They transfer at least one electron between two or more substrates, mediated by a cofactor (Milton and Minteer, 2017). The cofactors vary the oxidation state while catalysis is taking place, and there are several possible cofactors for oxidoreductases .…”