Direct electron transfer from graphite and functionalized gold electrodes to T1 and T2/T3 copper centers of bilirubin oxidase

Abstract

Direct electron transfer (DET) from bare spectrographic graphite (SPGE) or 3-mercaptopropionic acid-modified gold (MPA-gold) electrodes to Trachyderma tsunodae bilirubin oxidase (BOD) was studied under anaerobic and aerobic conditions by cyclic voltammetry and chronoamperometry. On cyclic voltammograms nonturnover Faradaic signals with midpoint potentials of about 700 mV and 400 mV were clearly observed corresponding to redox transformations of the T1 site and the T2/T3 cluster of the enzyme, respectively. The immobilized BOD was differently oriented on the two electrodes and its catalysis of O(2)-electroreduction was also massively different. On SPGE, where most of the enzyme was oriented with the T1 copper site proximal to the carbon with a quite slow ET process, well-pronounced DET-bioelectroreduction of O(2) was observed, starting already at >700 mV vs. NHE. In contrast, on MPA-gold most of the enzyme was oriented with its T2/T3 copper cluster proximal to the metal. Indeed, there was little DET-based catalysis of O(2)-electroreduction, even though the ET between the MPA-gold and the T2/T3 copper cluster of BOD was similar to that observed for the T1 site at SPGE. When BOD actively catalyzes the O(2)-electroreduction, the redox potential of its T1 site is 690 mV vs. NHE and that of one of its T2/T3 copper centers is 390 mV vs. NHE. The redox potential of the T2/T3 copper cluster of a resting form of BOD is suggested to be about 360 mV vs. NHE. These values, combined with the observed biocatalytic behavior, strongly suggest an uphill intra-molecular electron transfer from the T1 site to the T2/T3 cluster during the catalytic turnover of the enzyme.

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…[48] This suggests that the electrode can be recognized as the primary electron donor to the MCOs, and can provide direct access to the potential values for the T1 Cu centers (Table 1). [41,47,[49][50][51][52][53] The Cu II /Cu I transition of the T1 center for plant and fungal LACs are determined to be between + 0.22 and + 0.58 V vs. Ag/AgCl. [45] According to this potential, LACs are classified in low, middle, or high redox potential enzymes, the latter being the most interesting for applications in EBFCs.…”

“…[42][43] Noncatalytic voltametric signatures of MCOs in the absence of O 2 were difficult to assign, especially on gold electrodes, because of some discrepancy between the cyclic voltammetry (CV) potentials and the potential at which O 2 reduction occurred. [44][45][46][47] A mutant of Myrothecium verrucaria (Mv) BOD, displaying a lower Cu T1 redox potential, was however shown to catalyze O 2 reduction at a lower poten- CHEMELECTROCHEM REVIEWS www.chemelectrochem.org tial than the wild type. [48] This suggests that the electrode can be recognized as the primary electron donor to the MCOs, and can provide direct access to the potential values for the T1 Cu centers (Table 1).…”

“…Potential values for T2 and T3 centers are more difficult to evaluate because of the many intermediates with different geometries and oxidation states that are generated in the course of O 2 reduction. [47,52,[58][59][60] Some works however reported multiple noncatalytic redox waves for MCOs in the range + 0.2 to + 0.4 V vs. Ag/AgCl, most probably because of a different enzyme orientation depending on the electrode material. [47,[61][62] At least one of these processes might be attributed to a trinuclear cluster intermediate.…”

“…[47,52,[58][59][60] Some works however reported multiple noncatalytic redox waves for MCOs in the range + 0.2 to + 0.4 V vs. Ag/AgCl, most probably because of a different enzyme orientation depending on the electrode material. [47,[61][62] At least one of these processes might be attributed to a trinuclear cluster intermediate. [41,47,[63][64] An uphill intramolecular electron transfer was thus proposed, which was confirmed both by electrochemistry and quantum and molecular mechanical calculations.…”

Stable ‘Floating' Air Diffusion Biocathode Based on Direct Electron Transfer Reactions Between Carbon Particles and High Redox Potential Laccase

“…Detailed fundamental bioelectrochemical investigations of BMCO were performed using various planar electrodes [14]. It was discovered that carbon was superior, providing efficient O 2 bioelectroreduction at high potentials, whereas DET-based bioelectrocatalysis at metal electrodes seems to be much more complicated [20][21][22]. Thus, regarding the very efficient and stable BMCO-based biocathodes assembled and characterised so far, carbonaceous electrodes are preferred (e.g.…”