Nitrogenase and nitrogenase reductase associate and dissociate with each catalytic cycle

Area of Science:

• Biochemistry
• Enzymology
• Nitrogen Fixation Research

Background:

• Nitrogenase enzyme complex catalyzes nitrogen fixation.
• Interactions between nitrogenase (MoFe protein) and nitrogenase reductase (Fe protein) are crucial for electron transfer.
• Current nomenclature may not fully reflect functional roles.

Purpose of the Study:

• To investigate the dissociation kinetics of nitrogenase and nitrogenase reductase after electron transfer.
• To elucidate the relationship between ATP hydrolysis, electron transfer, and substrate reduction.
• To propose revised nomenclature for the nitrogenase complex components.

Main Methods:

• Kinetic analysis of hydrogen evolution following electron transfer.
• Measurement of ATP hydrolysis rates.
• Analysis of protein-protein interactions during the catalytic cycle.

Main Results:

• A lag phase, equivalent to nitrogenase turnover time, precedes hydrogen evolution, indicating protein dissociation after each electron transfer.
• Random association between nitrogenase reductase and nitrogenase facilitates electron distribution.
• ATP hydrolysis occurs without a lag, coupled to electron transfer, not substrate reduction.

Conclusions:

• Nitrogenase and nitrogenase reductase dissociate after each electron transfer event.
• ATP hydrolysis is directly coupled to electron transfer from nitrogenase reductase to nitrogenase.
• The study supports renaming the MoFe protein as nitrogenase and the Fe protein as nitrogenase reductase for clarity.