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Positive cooperativity during Azotobacter vinelandii nitrogenase-catalyzed acetylene reduction
Steven Truscott1, Randy S Lewis2, G D Watt1
1Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84604, United States of America.
Biophysical Chemistry
|July 9, 2021
Summary
This study reveals how the nitrogenase enzyme
Area of Science:
- Biochemistry
- Enzymology
- Nitrogen Fixation Research
Background:
- The nitrogenase enzyme complex, crucial for biological nitrogen fixation, comprises a MoFe protein and an Fe protein.
- The MoFe protein contains P and FeMoco centers, acting as the substrate reduction site.
- The Fe protein serves as the specific reductant for the MoFe protein, utilizing ATP.
Purpose of the Study:
- To investigate the independent or cooperative function of the two symmetrical halves of the MoFe protein during nitrogenase catalysis.
- To elucidate the mechanism of inhibition by varying Fe protein ratios and its effect on different reduction reactions.
- To propose a mechanistic model explaining the observed cooperativity in acetylene reduction.
Main Methods:
- Formation of transition-state complexes between the MoFe protein and Fe protein of Azotobacter vinelandii with varying ratios.
- Measurement of specific activity for 2H+ reduction to H2 and acetylene reduction to ethylene.
- Development and application of a mechanistic model to analyze inhibition patterns and cooperativity.
Main Results:
- Specific activity decreased with increasing Fe protein/MoFe protein ratio.
- H+ reduction inhibition was linear, suggesting independent site function, while acetylene reduction inhibition showed non-linear behavior, indicating cooperativity.
- The mechanistic model predicted independent site function for H+ reduction and positive cooperativity for acetylene reduction.
Conclusions:
- The MoFe protein exhibits distinct catalytic behaviors for H+ and acetylene reduction.
- Acetylene reduction involves a cooperative mechanism between the two halves of the MoFe protein, unlike H+ reduction.
- A new paradigm for MoFe protein catalytic function is proposed, highlighting inter-site communication during nitrogenase catalysis.
Keywords:
Kinetic modelMoFe proteinNitrogenasePositive cooperativitySynchronous kineticsTransition-state complexMore Related Videos
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