Direct Heterogeneous Electron Transfer Reactions of Bacillus halodurans Bacterial Blue Multicopper Oxidase

Abstract

Direct electron transfer reactions of Bacillus halodurans bacterial multicopper oxidase on bare spectrographic graphite, as well as bare and thiol-modified gold electrodes were studied using cyclic voltammetry, potentiometry, amperometry, and spectroelectrochemistry. The redox potential of the T1 site of the enzyme was measured using mediatorless redox titration and found to be 325 mV AE 10 mV vs. NHE. From measurements with a mercaptopropionic acid-modified gold electrode under aerobic conditions a midpoint potential of 360 mV vs. NHE for the T2/T3 copper cluster is deduced. Differing from most other characterized laccases of fungal and plant origins this bacterial enzyme exhibits bioelectrocatalytic activity at neutral pH and tolerates high chloride concentrations (200 mM), conditions that usually strongly inhibit catalysis. Moreover, it has the very high affinity towards molecular oxygen both in solution and in the adsorbed state (K M 50 mM).

The Thermophilic CotA Laccase from Bacillus subtilis: Bioelectrocatalytic Evaluation of O2 Reduction in the Direct and Mediated Electron Transfer Regime

“…In presence of O 2 , an unambiguous reduction current could be recorded. This result indicates that CotA laccase is, like many other laccases [21,22,36,37], able to transfer electrons directly from the T1 Cu-site to the electrode surface. The redox potential of the T1 Cu-site (at 25 8C, pH 7.6) was previously determined by spectroscopic redox titration to be 245 mV [38] or 315 mV vs. Ag/AgCl 3 M KCl [39].…”

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.…”

“…Bacillus pumilus (Bp) [71] Bacterium BOD temp., urate, Cl À 32/391 Bacillus halodurans [53] Bacterium BOD 0.115 [c] n.d. Magnaporthe oryzae [72] Fungus BOD urea 429/664 Bacillus subtilis [318][319] Bacterium BOD temp. 124/322 Rhus vernicifera [56] Plant LAC 0.22 [b] 103/560 [320] Trametes hirsute (Th) [56] Fungus LAC 0.57 [b] 220/210 Sreptomyces coelicolor (Sc) [57] Bacterium LAC 0.47 (pH 5.5) [c] 3600/5.8 [321] E. coli [329] Bacterium CcO aa3 0.2/n.d.…”

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

“…Later this occurrence was identified in many other redox enzymes including different BMCO, e.g. ascorbate oxidase [8,9] and bilirubin oxidase [10,11], as well as fungal [12][13][14][15], plant [12,16] and bacterial [17,18] Lcs. BMCO contain four copper ions which are historically classified into three types according to their spectroscopic characteristics, viz.…”