Efficient Direct Electron Transfer for a Highly Oriented PQQ-GDH Immobilized Electrode for Bioanode

Abstract

A bioanode with improved enzyme orientation was developed to achieve an efficient enzyme reaction and electron transfer on an electrode surface. A highly stable PQQ-dependent glucose dehydrogenase (PQQ-GDH) isolated from a hyper-thermophilic archaeon was employed as an electron conversion element. PQQ-GDH is expected to maintain battery properties and to have a long battery life. To immobilize the enzyme onto the electrode with appropriate orientation, we introduced a His-tag to the N-terminal of PQQ-GDH by a genetic technique and utilized the affinity bond between His-tag and Cu atoms. The catalytic current density in the presence of substrate was 18.6 μA/cm2 without a mediator. The current density of the oriented electrode was approximately 90 times higher than that of the non-oriented electrode. By immobilizing the enzyme with orientation, the accessibility between the enzyme and substrate for enzyme reaction increased because the active site of PQQ-GDH is located opposite the electrode. Because enzymes have different orientations at the surface of the non-orientated electrode, the efficiency of the electrode was lower than that of the high-orientation electrode. The results of the present study present a potentially promising finding for application to practical bioelectric devices, such as bio-fuel cells and biosensors.