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Title: Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2

Abstract

Of the three forms of nitrogenase (Mo-nitrogenase, V-nitrogenase, and Fe-nitrogenase), Fe-nitrogenase has the poorest ratio of N2 reduction relative to H2 evolution. Current work on the Mo-nitrogenase has revealed that reductive elimination of two bridging Fe–H–Fe hydrides on the active site FeMo-cofactor to yield H2 is a key feature in the N2 reduction mechanism. The N2 reduction mechanism for the Fe-nitrogenase active site FeFe-cofactor was unknown. Here, we have purified both component proteins of the Fe-nitrogenase system, the electron-delivery Fe protein (AnfH) plus the catalytic FeFe protein (AnfDGK), and established its mechanism of N2 reduction. Inductively coupled plasma optical emission spectroscopy and mass spectrometry illustrate that the FeFe protein component does not contain significant amounts of Mo or V, thus ruling out a requirement of these metals for N2 reduction. The fully functioning Fe-nitrogenase system was found to have specific activities for N2 reduction (1 atm) of 181 ± 5 nmol NH3 min–1 mg–1 FeFe protein, for proton reduction (in the absence of N2) of 1085 ± 41 nmol H2 min–1 mg–1 FeFe protein, and for acetylene reduction (0.3 atm) of 306 ± 3 nmol C2H4 min–1 mg–1 FeFe protein. Under turnover conditions, N2 reduction is inhibited by H2 andmore » the enzyme catalyzes the formation of HD when presented with N2 and D2. These observations are explained by the accumulation of four reducing equivalents as two metal-bound hydrides and two protons at the FeFe-cofactor, with activation for N2 reduction occurring by reductive elimination of H2.« less

Authors:
ORCiD logo [1];  [2];  [1];  [2];  [3];  [3]; ORCiD logo [2];  [4]; ORCiD logo [2]; ORCiD logo [1]
  1. Utah State Univ., Logan, UT (United States)
  2. Northwestern Univ., Evanston, IL (United States)
  3. Montana State Univ., Bozeman, MT (United States)
  4. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)
Publication Date:
Research Org.:
Montana State Univ., Bozeman, MT (United States). Energy Frontier Resarch Center (EFRC) Center for Biological Electron Transfer and Catalysis (BETCy)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1470112
Grant/Contract Number:  
SC0012518
Resource Type:
Accepted Manuscript
Journal Name:
Biochemistry
Additional Journal Information:
Journal Volume: 57; Journal Issue: 5; Related Information: BETCy partners with Montana State University (lead); Arizona State University; National Renewable Energy Laboratory; University of Georgia; University of Kentucky; University of Washington; Utah State University; Journal ID: ISSN 0006-2960
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Alternative nitrogenase; catalysis; N2 reduction; nitrogen fixation

Citation Formats

Harris, Derek F., Lukoyanov, Dmitriy A., Shaw, Sudipta, Compton, Phil, Tokmina-Lukaszewska, Monika, Bothner, Brian, Kelleher, Neil, Dean, Dennis R., Hoffman, Brian M., and Seefeldt, Lance C. Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2. United States: N. p., 2017. Web. doi:10.1021/acs.biochem.7b01142.
Harris, Derek F., Lukoyanov, Dmitriy A., Shaw, Sudipta, Compton, Phil, Tokmina-Lukaszewska, Monika, Bothner, Brian, Kelleher, Neil, Dean, Dennis R., Hoffman, Brian M., & Seefeldt, Lance C. Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2. United States. doi:10.1021/acs.biochem.7b01142.
Harris, Derek F., Lukoyanov, Dmitriy A., Shaw, Sudipta, Compton, Phil, Tokmina-Lukaszewska, Monika, Bothner, Brian, Kelleher, Neil, Dean, Dennis R., Hoffman, Brian M., and Seefeldt, Lance C. Thu . "Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2". United States. doi:10.1021/acs.biochem.7b01142. https://www.osti.gov/servlets/purl/1470112.
@article{osti_1470112,
title = {Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2},
author = {Harris, Derek F. and Lukoyanov, Dmitriy A. and Shaw, Sudipta and Compton, Phil and Tokmina-Lukaszewska, Monika and Bothner, Brian and Kelleher, Neil and Dean, Dennis R. and Hoffman, Brian M. and Seefeldt, Lance C.},
abstractNote = {Of the three forms of nitrogenase (Mo-nitrogenase, V-nitrogenase, and Fe-nitrogenase), Fe-nitrogenase has the poorest ratio of N2 reduction relative to H2 evolution. Current work on the Mo-nitrogenase has revealed that reductive elimination of two bridging Fe–H–Fe hydrides on the active site FeMo-cofactor to yield H2 is a key feature in the N2 reduction mechanism. The N2 reduction mechanism for the Fe-nitrogenase active site FeFe-cofactor was unknown. Here, we have purified both component proteins of the Fe-nitrogenase system, the electron-delivery Fe protein (AnfH) plus the catalytic FeFe protein (AnfDGK), and established its mechanism of N2 reduction. Inductively coupled plasma optical emission spectroscopy and mass spectrometry illustrate that the FeFe protein component does not contain significant amounts of Mo or V, thus ruling out a requirement of these metals for N2 reduction. The fully functioning Fe-nitrogenase system was found to have specific activities for N2 reduction (1 atm) of 181 ± 5 nmol NH3 min–1 mg–1 FeFe protein, for proton reduction (in the absence of N2) of 1085 ± 41 nmol H2 min–1 mg–1 FeFe protein, and for acetylene reduction (0.3 atm) of 306 ± 3 nmol C2H4 min–1 mg–1 FeFe protein. Under turnover conditions, N2 reduction is inhibited by H2 and the enzyme catalyzes the formation of HD when presented with N2 and D2. These observations are explained by the accumulation of four reducing equivalents as two metal-bound hydrides and two protons at the FeFe-cofactor, with activation for N2 reduction occurring by reductive elimination of H2.},
doi = {10.1021/acs.biochem.7b01142},
journal = {Biochemistry},
number = 5,
volume = 57,
place = {United States},
year = {2017},
month = {12}
}

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Works referenced in this record:

The Mechanism Of N2 Reduction Catalyzed By Fe-Nitrogenase Involves Reductive Elimination Of H2
dataset, January 2017


The Mechanism Of N2 Reduction Catalyzed By Fe-Nitrogenase Involves Reductive Elimination Of H2
dataset, January 2017


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