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Title: Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E 2 (2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis

Abstract

Early studies in which nitrogenase was freeze-trapped during enzymatic turnover revealed the presence of high-spin (S = 3/2) electron paramagnetic resonance (EPR) signals from the active-site FeMo-cofactor (FeMo-co) in electron-reduced intermediates of the MoFe protein. Historically denoted as 1b and 1c, each of the signals is describable as a fictitious spin system, S' = 1/2, with anisotropic g' tensor, 1b with g' = [4.21, 3.76, ?] and 1c with g' = [4.69, ~3.20, ?]. A clear discrepancy between the magnetic properties of 1b and 1c and the kinetic analysis of their appearance during pre-steady-state turnover left their identities in doubt, however. We subsequently associated 1b with the state having accumulated 2[e/H+], denoted as E2(2H), and suggested that the reducing equivalents are stored on the catalytic FeMo-co cluster as an iron hydride, likely an [Fe–H–Fe] hydride bridge. Intra-EPR cavity photolysis (450 nm; temperature-independent from 4 to 12 K) of the E2(2H)/1b state now corroborates the identification of this state as storing two reducing equivalents as a hydride. Photolysis converts E2(2H)/1b to a state with the same EPR spectrum, and thus the same cofactor structure as pre-steady-state turnover 1c, but with a different active-site environment. Upon annealing of the photogenerated state atmore » temperature T = 145 K, it relaxes back to E2(2H)/1b. This implies that the 1c signal comes from an E2(2H) hydride isomer of E2(2H)/1b that stores its two reducing equivalents either as a hydride bridge between a different pair of iron atoms or an Fe–H terminal hydride.« less

Authors:
 [1];  [2]; ORCiD logo [2];  [3]; ORCiD logo [2]; ORCiD logo [1]
  1. Departments of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, United States
  2. Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
  3. Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
Publication Date:
Research Org.:
Utah State Univ., Logan, UT (United States); Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Northwestern Univ., Evanston, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Inst. of Health (NIH) (United States)
OSTI Identifier:
1429515
Alternate Identifier(s):
OSTI ID: 1508781
Grant/Contract Number:  
SC0010687; SC0010834; GM111097
Resource Type:
Journal Article: Published Article
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Name: Inorganic Chemistry Journal Volume: 57 Journal Issue: 12; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Lukoyanov, Dmitriy A., Khadka, Nimesh, Yang, Zhi-Yong, Dean, Dennis R., Seefeldt, Lance C., and Hoffman, Brian M. Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E 2 (2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis. United States: N. p., 2018. Web. doi:10.1021/acs.inorgchem.8b00271.
Lukoyanov, Dmitriy A., Khadka, Nimesh, Yang, Zhi-Yong, Dean, Dennis R., Seefeldt, Lance C., & Hoffman, Brian M. Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E 2 (2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis. United States. https://doi.org/10.1021/acs.inorgchem.8b00271
Lukoyanov, Dmitriy A., Khadka, Nimesh, Yang, Zhi-Yong, Dean, Dennis R., Seefeldt, Lance C., and Hoffman, Brian M. 2018. "Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E 2 (2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis". United States. https://doi.org/10.1021/acs.inorgchem.8b00271.
@article{osti_1429515,
title = {Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E 2 (2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis},
author = {Lukoyanov, Dmitriy A. and Khadka, Nimesh and Yang, Zhi-Yong and Dean, Dennis R. and Seefeldt, Lance C. and Hoffman, Brian M.},
abstractNote = {Early studies in which nitrogenase was freeze-trapped during enzymatic turnover revealed the presence of high-spin (S = 3/2) electron paramagnetic resonance (EPR) signals from the active-site FeMo-cofactor (FeMo-co) in electron-reduced intermediates of the MoFe protein. Historically denoted as 1b and 1c, each of the signals is describable as a fictitious spin system, S' = 1/2, with anisotropic g' tensor, 1b with g' = [4.21, 3.76, ?] and 1c with g' = [4.69, ~3.20, ?]. A clear discrepancy between the magnetic properties of 1b and 1c and the kinetic analysis of their appearance during pre-steady-state turnover left their identities in doubt, however. We subsequently associated 1b with the state having accumulated 2[e–/H+], denoted as E2(2H), and suggested that the reducing equivalents are stored on the catalytic FeMo-co cluster as an iron hydride, likely an [Fe–H–Fe] hydride bridge. Intra-EPR cavity photolysis (450 nm; temperature-independent from 4 to 12 K) of the E2(2H)/1b state now corroborates the identification of this state as storing two reducing equivalents as a hydride. Photolysis converts E2(2H)/1b to a state with the same EPR spectrum, and thus the same cofactor structure as pre-steady-state turnover 1c, but with a different active-site environment. Upon annealing of the photogenerated state at temperature T = 145 K, it relaxes back to E2(2H)/1b. This implies that the 1c signal comes from an E2(2H) hydride isomer of E2(2H)/1b that stores its two reducing equivalents either as a hydride bridge between a different pair of iron atoms or an Fe–H terminal hydride.},
doi = {10.1021/acs.inorgchem.8b00271},
url = {https://www.osti.gov/biblio/1429515}, journal = {Inorganic Chemistry},
issn = {0020-1669},
number = 12,
volume = 57,
place = {United States},
year = {Sat Mar 24 00:00:00 EDT 2018},
month = {Sat Mar 24 00:00:00 EDT 2018}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at https://doi.org/10.1021/acs.inorgchem.8b00271

Citation Metrics:
Cited by: 17 works
Citation information provided by
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Figures / Tables:

Figure 1 Figure 1: Electron accumulation phase of the Lowe−Thorneley kinetic scheme for nitrogen fixation, including hydride protonation relaxation reactions that link the Kramers (half-integer spin) intermediates depicted below. En represents the MoFe protein state in which the catalytic FeMo-co cluster has accumulated n electrons from the Fe protein cycle plus nmore » protons. The n = 4 state is activated by reductive elimination (re) of H2 to bind N2 and cleave the N≡N bond.« less

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Works referencing / citing this record:

A model for dinitrogen binding in the E 4 state of nitrogenase
journal, January 2019


Critical computational analysis illuminates the reductive-elimination mechanism that activates nitrogenase for N 2 reduction
journal, October 2018


Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.