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Nitrite, a new substrate for nitrogenase.

S A Vaughn1, B K Burgess

  • 1Department of Molecular Biology and Biochemistry, University of California, Irvine 92717.

Biochemistry
|January 24, 1989
PubMed
Summary

Azotobacter vinelandii nitrogenase (Av1 and Av2) does not react with nitrate. However, nitrite irreversibly inhibits the Fe protein and reversibly diverts electrons, demonstrating nitrogenase

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Area of Science:

  • Biochemistry
  • Microbiology
  • Enzymology

Background:

  • Nitrogenase is a crucial enzyme for nitrogen fixation in microorganisms.
  • Azotobacter vinelandii nitrogenase consists of two component proteins: Av1 and Av2.
  • Understanding the reactivity of nitrogenase with other nitrogen compounds is essential.

Purpose of the Study:

  • To investigate the reactivity of purified Azotobacter vinelandii nitrogenase (Av1 and Av2) components with nitrate and nitrite.
  • To elucidate the mechanisms of inhibition and electron diversion by nitrite.

Main Methods:

  • Purification of Azotobacter vinelandii nitrogenase component proteins (Av1 and Av2).
  • Assays for H2 evolution and C2H2 reduction in the presence of nitrate and nitrite.
  • Analysis of nitrite inhibition components (irreversible and reversible) and the effect of MgATP and CO.

Main Results:

  • Nitrate showed no effect on H2 evolution or C2H2 reduction by nitrogenase.
  • Nitrite dramatically inhibited H2 evolution through both irreversible and reversible mechanisms.
  • Irreversible inhibition was attributed to nitrite inactivation of the Fe protein, enhanced by MgATP.
  • Reversible inhibition involved electron diversion to the six-electron reduction of nitrite to ammonia.

Conclusions:

  • Azotobacter vinelandii nitrogenase does not interact with nitrate.
  • Nitrite acts as an inhibitor of nitrogenase activity.
  • Nitrogenase possesses nitrite reductase activity, reducing nitrite to ammonia.

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