Investigating the Molybdenum Nitrogenase Mechanistic Cycle Using Spectroelectrochemistry

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Electrochemistry

Background:

• Molybdenum nitrogenase is vital for biological nitrogen fixation, converting N2 to NH3.
• The precise catalytic mechanisms, including electron and proton transfer, are not fully understood.

Purpose of the Study:

• To investigate the catalytic mechanism of molybdenum nitrogenase using a biohybrid electrochemical system.
• To elucidate the role of specific amino acid residues and intermediates in nitrogenase catalysis.

Main Methods:

• Covalent attachment of molybdenum nitrogenase (MoFe) to gold electrodes.
• Utilizing surface-enhanced infrared absorption spectroscopy (SEIRA) coupled with electrochemistry.
• Performing quantum mechanics/molecular mechanics (QM/MM) calculations.

Main Results:

• Observed terminal and bridging S-H stretching frequencies during nitrogenase turnover, indicating protonation of bridging sulfides in FeMoco.
• Provided direct experimental evidence for the role of these protonated sulfides in catalysis.
• Investigated CO inhibition, revealing CO binding and unbinding dynamics under electrochemical conditions.

Conclusions:

• The study provides novel insights into the mechanistic cycle of molybdenum nitrogenase.
• Established a foundation for studying other nitrogenases, such as vanadium and iron nitrogenases.
• Demonstrated the utility of biohybrid electrochemical systems for mechanistic studies of metalloenzymes.