A collaborative effort led by researchers of the DeBeer department has shed light on the catalytic mechanism of molybdenum nitrogenase, an enzyme crucial to the biological nitrogen cycle. Nitrogenase plays a key role in converting atmospheric nitrogen (N₂) into ammonia (NH₃) under ambient conditions—a process of immense agronomic and environmental importance. Unlike the energy-intensive Haber-Bosch process, nitrogenase achieves this feat using minimal energy. Despite significant progress in understanding the enzyme's catalytic mechanism, there are still a lot of open questions, especially concerning electron and proton transfer dynamics.
In this groundbreaking study, the molybdenum-based nitrogenase protein (MoFe) was covalently attached to gold electrodes, enabling researchers to use a mild mediator to mimic the natural electron flow to its active site, FeMoco. Using advanced spectroelectrochemical techniques, the team experimentally observed, for the first time, both terminal and bridging S-H stretching frequencies. These observations provide direct evidence of protonation of FeMoco’s bridging sulfides during enzymatic turnover—an essential step in the catalytic cycle.
Key findings also include insights into CO inhibition, where the team characterized CO binding and unbinding dynamics at the enzyme's active site under electrochemical conditions.
This work highlights the synergy between experimental and theoretical approaches, utilizing surface-enhanced infrared absorption spectroscopy (SEIRA) coupled with quantum mechanical/molecular mechanical (QM/MM) calculations. The findings are expected to inspire future studies on alternative nitrogenases, such as vanadium- and iron-based systems, and their application in sustainable nitrogen fixation and biohybrid catalysis.
The open access paper was recently published in the Journal of the American Chemical Society.
Lead Authors: Kushal Sengupta, Olaf Rüdiger, Serena DeBeer
Original Paper: Kushal Sengupta, Justin P. Joyce, Laure Decamps, Liqun Kang, Ragnar Bjornsson, Olaf Rüdiger, and Serena DeBeer. Investigating the Molybdenum Nitrogenase Mechanistic Cycle Using Spectroelectrochemistry (2025) Journal of the American Chemical Society Article ASAP DOI: 10.1021/jacs.4c16047 Link