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 »
- Authors:
-
- Departments of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, United States
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
- 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}
}
Web of Science
Figures / Tables:
Works referencing / citing this record:
Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies: Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies
journal, February 2019
- Hong, Dae Ho; Murray, Leslie J.
- European Journal of Inorganic Chemistry, Vol. 2019, Issue 15
A model for dinitrogen binding in the E 4 state of nitrogenase
journal, January 2019
- Thorhallsson, Albert Th.; Benediktsson, Bardi; Bjornsson, Ragnar
- Chemical Science, Vol. 10, Issue 48
Critical computational analysis illuminates the reductive-elimination mechanism that activates nitrogenase for N 2 reduction
journal, October 2018
- Raugei, Simone; Seefeldt, Lance C.; Hoffman, Brian M.
- Proceedings of the National Academy of Sciences, Vol. 115, Issue 45
Figures / Tables found in this record: