Enhanced direct electron transfer-type bioelectrocatalysis of bilirubin oxidase on negatively charged aromatic compound-modified carbon electrode

• Negatively charged aromatic character on electrodes increases DET-type bioelectrocatalytic current of BOD.
• Electrostatic interaction between enzyme and electrode induces an orientation suitable for bioelectrocatalysis of BOD.
• The modification causes an increase in the electron transfer rate constant and a decrease in randomness of orientation.
• The basic idea is applicable to copper efflux oxidase in an opposed sign.

Effects of chemical modification of mesoporous Ketjen Black (KB) electrodes on direct electron transfer (DET)-type bioelectrocatalytic reduction of dioxygen by bilirubin oxidase (BOD) were investigated under air-saturated neutral conditions. Several amines were electrochemically oxidized at KB-modified electrode to generate nitrogen–carbon bond. The modification with negatively charged aromatic amines such as 4-aminobenzoic acid (4-ABA) drastically increased the catalytic current density compared with that by positively charged and non-charged aromatic compounds and negatively charged non-aromatic compound. Considering the basic amino acid residues around the type I site of BOD, it can be concluded that weakly negative charge on electrode surface induces a favorable orientation of BOD for the DET-type catalysis via the electrostatic interaction, while the π–π interaction is also essential for effective orientation of BOD on the electrode surface. The 4-ABA-modification leads to an increase in the heterogeneous electron transfer rate constant and a decrease in the randomness of the orientation as well as a slight increase in the surface concentration of BOD.

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