Enzymatic X-ray absorption spectroelectrochemistry

Understanding the redox properties and catalytic behavior of proteins is critical for harnessing their functions in biocatalysis and to promote efficient bio-inspired catalysts design. Enzymatic X-ray absorption spectroelectrochemistry (XA-SEC) combines the insights of X-ray absorption spectroscopy with the precision of electrochemical methods to elucidate enzymes' redox properties and catalytic behavior. Here we describe how to perform enzymatic XA-SEC experiments. The procedure begins with the preparation of the carbon-based working electrode to enhance enzyme immobilization. We exemplify with the efficient immobilization of bilirubin oxidase from Myrothecium verrucaria on the electrode surface, utilizing nanomaterials to enhance biomaterial loading and electron-transfer at the enzyme-electrode interface. Next, we guide researchers through setting up a standard three-electrode electrochemical cell, ensuring proper electrical connections and electrolyte preparation. Our Protocol details the Cu K-edge X-ray absorption spectroscopy measurement procedure at the synchrotron light sources, with in situ electrochemical control. Real-time redox processes are monitored through direct electron transfer analysis, providing valuable thermodynamic and kinetic information. It is important to determine the stability and activity of the analyzed protein under X-ray beam exposure; our approach typically results in stable electrochemical and spectroscopic signals for long experimental runs, showcasing the enzyme's robust performance and efficient protein immobilization. The method's ability to correlate XA-SEC data with direct electron transfer and substrate-biding analysis provides a powerful tool for advancing our understanding of enzymatic electrocatalysis and opens new avenues for developing sustainable bioelectrochemical technologies.