Conjugation of Electrochemical and Enzymic Reactions

According to the c scheme, all reaction components (substrate, mediator, and enzyme) are present in a solubilized state. The reaction takes place in the bulk solution, while the electron transport is effected by a low-molecular weight carrier. According to schemes d and e, one of the components, either the mediator or enzyme, is immobilized, but electron transfer is brought about by the mediator. 

In order that a compound be used as a mediator, it must satisfy quite a number of requirements 1) the interaction stage between the mediator and the enzyme active center must be fast (the mediator must be a specific substrate of the enzyme) 2) the normal oxidation-reduction potential of the mediator must be close to that of the reaction concerned 3) the mediator should be subject to electrochemical oxidation (or reduction) on the electrode made from a given material under conditions close to reversible ones. By no means are all of the known mediators able to meet the above requirements. In Table 3 the characteristics of certain mediator compounds which have been used in bioelectrocatalysis are given. 

In the course of work on bioelectrocatalysis all three ways of using enzymes to accelerate electrochemical reactions have been taken into account. These research areas cover the following electrochemical reactions hydrogen, oxygen, and oxidation reactions of certain organic compounds. In each case, different methods were employed to achieve the conjugation of enzymatic and electrochemical reactions. 

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