Electron Transfer in the Mediatorless Method of Bioelectrocatalysis

The observations listed above enable us to conclude that under the conditions of mediatorless bioelectrocatalysis, the adsorbed enzymes are functioning in a state close to the native one. Therefore, there is no basis for the assumption that the orbitals of the metal atom or of any other groups in the active center overlap with those of the electroconductive substrate. In the presence of such a direct overlap we would expect a significant change in the functioning mechanism of the active center. Moreover, the active center of the enzymes lies, as a rule, rather deep in the hydrophobic space of the protein globule.  

Therefore, it appears reasonable to assume the existence of the tunneling mechanism of electron transfer between the electrode and the enzyme active center. The possibility of a sub-barrier electron transfer at large distances (10-20 A) has been shown, at least theoretically, for electrochemical systems and is widely used to discuss electron transport in biological systems.  

For different models of the tunneling mechanism of electron transfer the rate of this process is given by the expression 

Nonetheless, the concepts of tunneling for electron transfer are quite promising for the interpretation of certain effects of bioelectrocatalysis. 

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