Journal
ELECTROCHIMICA ACTA
Volume 429, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2022.140987
Keywords
Multicopper oxidase; Copper efflux oxidase; Direct electron transfer; Bioelectrochemistry; Cu2+ effects
Categories
Funding
- JSPS Overseas Challenge Program for Young Researchers
- National Research Agency (ANR, France) [ANR-21-CE44-0024]
- CNRS, France
- Agence Nationale de la Recherche (ANR) [ANR-21-CE44-0024] Funding Source: Agence Nationale de la Recherche (ANR)
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This study investigated the effects of Cu2+ on the bioelectrocatalytic reduction of O2 by CueO, and found that Cu2+ decreased the activity of CueO and caused inactivation and reactivation processes. Kinetic analysis and pseudo-steady-state analysis revealed the relationship between Cu2+ and the enzymatic activity.
Copper efflux oxidases (CueOs) are key enzymes in copper homeostasis systems. The mechanisms involved are however largely unknown. CueO-type enzymes share a typical structural feature composed of Methionine-rich (Met-rich) domains that are proposed to be involved in copper homeostasis. Bioelectrocatalysis using CueO-type enzymes in the presence of Cu2+ recently highlighted a new Cu2+-dependent catalytic pathway related to a cuprous oxidase activity. In this work, we further investigated the effects of Cu2+ on direct electron transfer (DET)-type bioelectrocatalytic reduction of O2 by CueO at NH2-functionalized multi-walled carbon nanotubes. The DET-type bioelectrocatalytic activity of CueO decreased at low potential in the presence of Cu2+, showing unique peak-shaped voltammograms that we attribute to inactivation and reactivation processes. Chro-noamperometry was used to kinetically analyze these processes, and the results suggested linear free energy relationships between the inactivation/reactivation rate constant and the electrode potential. Pseudo -steady-state analysis also indicated that Cu2+ uncompetitively inhibited the enzymatic activity. A detailed model for the Cu2+-dependent reductive inactivation of CueO was proposed to explain the electrochemical data, and the related thermodynamic and kinetic parameters. A CueO variant with truncated copper-binding alpha helices and bilirubin oxidase free of Met-rich domains also showed such reductive inactivation process, which suggests that multicopper oxidases contain copper-binding sites that lead to inactivation.
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