Direct electrochemical studies of biological ET reactions with redox enzymes enable the development of highly efficient bioelectrocatalysts of interest. The obligatory condition for these studies is the existence of a direct electronic communication between the electrode and the enzyme redox active sites. When enzyme-electrode interactions provide this, then direct bioelectrocatalysis can be studied under conditions when the electrode replaces the natural redox partner of the enzyme. However, direct ET of the enzymes at the electrodes is sometimes not attained or accompanied by the loss of enzymatic activity, as in the case of multicofactor-containing enzymes, which successful operation at the electrode requires internal ET between their active sites in addition to the electrode-enzyme ET reaction. Mimicking the natural environment of these enzymes by the modified electrodes is then of particular interest. Therewith, a simulation of the molecular surfaces of the enzyme biological partners by self-assembled monolayers of alkanethiols may provide the necessary amount/orientation of the enzyme molecules for direct ET reaction with the electrode, as well as a conformation appropriate for efficient intramolecular ET.
It is discussed how the choice of the electrode material/electrode modification and solution composition affect ET reactions of heme-containing enzymes. Direct ET reactions between the electrodes and cytochrome c, a model ET enzyme, as well as direct bioelectrocatalysis of H2O2 reduction based on direct ET from the electrode to the heme active site of horseradish peroxidase, one of the most studied members of the family of the heme enzymes, are covered in detail. It is also reported how the choice of alkanethiols of different polarity/hydrophobicity and charge might provide the surface properties of the electrodes necessary for adsorption and orientation of the multicofactor heme-containing enzymes favourable for efficient electrode-assisted biocatalysis.