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

Journal Article · · Biochemistry

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.

Research Organization:
Montana State Univ., Bozeman, MT (United States). Energy Frontier Resarch Center (EFRC) Center for Biological Electron Transfer and Catalysis (BETCy)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0012518
OSTI ID:
1470112
Journal Information:
Biochemistry, Journal Name: Biochemistry Journal Issue: 5 Vol. 57; ISSN 0006-2960
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (5)

Reduction and Condensation of Aldehydes by the Isolated Cofactor of Nitrogenase journal October 2018
Exploring the alternatives of biological nitrogen fixation journal January 2018
Theory-guided materials design: two-dimensional MXenes in electro- and photocatalysis journal January 2019
Facile, cost-effective plasma synthesis of self-supportive FeS x on Fe foam for efficient electrochemical reduction of N 2 under ambient conditions journal January 2019
Reconstructing the evolutionary history of nitrogenases: Evidence for ancestral molybdenum‐cofactor utilization journal February 2020

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