Anthraquinone 2-carboxylic acid as an electron shuttling mediator and attached electron relay for horseradish peroxidase

Horseradish peroxidase (HRP)-modified electrodes are among the most frequently used detectors for measuring the amount of H2O2 as well as organic hydroperoxides. The major requirement for the construction of HRP-modified electrodes is to establish a fast and efficient electron transfer contact between the electrode surface and the redox center of peroxidase. To establish such a communication, we examined anthraquinone 2-carboxylic acid (AQ) as a novel electron shuttling mediator and attached electron relay for HRP. Cyclic voltammetric results showed that dissolved AQ molecules are able to shuttle electrons between the heme site of HRP and the glassy carbon electrode. Covalent attachment of AQ molecules to the lysine residues of HRP established a direct electrical communication between the modified enzyme and the conventional electrode. In both cases, the glassy carbon electrode exhibited high current responses to H2O2. Moreover, the chemical modification of HRP with AQ enhanced the catalytic activity of the enzyme by 11%.