Infrared spectroscopy of the nitrogenase MoFe protein under electrochemical control: potential-triggered CO binding

• Published in: Chemical science (Cambridge) 2017, Vol.8 (2), p.1500-1505
• Main Authors: Paengnakorn, P, Ash, P A, Shaw, S, Danyal, K, Chen, T, Dean, D R, Seefeldt, L C, Vincent, K A
• Format: Article
• Language: English
• Subjects: Attenuation; Binding; Carbon monoxide; Chemistry; Corrosion inhibitors; Infrared; Infrared spectroscopy; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Proteins; Reduction
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c6sc02860h

We demonstrate electrochemical control of the nitrogenase MoFe protein, in the absence of Fe protein or ATP, using europium(iii/ii) polyaminocarboxylate complexes as electron transfer mediators. This allows the potential dependence of proton reduction and inhibitor (CO) binding to the active site FeMo-cofactor to be established. Reduction of protons to H is catalyzed by the wild type MoFe protein and β-98 and β-99 variants of the MoFe protein at potentials more negative than -800 mV ( SHE), with greater electrocatalytic proton reduction rates observed for the variants compared to the wild type protein. Electrocatalytic proton reduction is strongly attenuated by carbon monoxide (CO), and the potential-dependence of CO binding to the FeMo-cofactor is determined by infrared (IR) spectroelectrochemistry. The vibrational wavenumbers for CO coordinated to the FeMo-cofactor are consistent with earlier IR studies on the MoFe protein with Fe protein/ATP as reductant showing that electrochemically generated states of the protein are closely related to states generated with the native Fe protein as electron donor.