Abstract

Nitrogenases are responsible for biological nitrogen fixation, a crucial step in the biogeochemical nitrogen cycle. These enzymes utilize a two-component protein system and a series of iron–sulfur clusters to perform this reaction, culminating at the FeMco active site (M = Mo, V, Fe), which is capable of binding and reducing N2 to 2NH3. In this review, we summarize how different spectroscopic approaches have shed light on various aspects of these enzymes, including their structure, mechanism, alternative reactivity, and maturation. Synthetic model chemistry and theory have also played significant roles in developing our present understanding of these systems and are discussed in the context of their contributions to interpreting the nature of nitrogenases. Despite years of significant progress, there is still much to be learned from these enzymes through spectroscopic means, and we highlight where further spectroscopic investigations are needed.

Highlights

  • The conversion of atmospheric dinitrogen (N2) to bioavailable ammonia (NH3) is essential for life on earth and is a critical step in the biogeochemical nitrogen cycle

  • While N2 is abundant in the atmosphere, it is largely inert and must be fixed in a form that can be utilized by organisms for incorporation into amino acids, the building blocks of proteins, and nucleic acids, the building block of deoxyribonucleic acid (DNA)

  • In the context of N2ase research, extended X-ray absorption fine structure (EXAFS) has been vital in providing M−L distance parameters, which were crucial in the earliest structural determination of FeMoco and continue to play a role in the identification and description of intermediates.[163,166,196−209] a major limitation of EXAFS is that the extracted distances reflect the average for all photoabsorbers of a given type

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Summary

Similarities and Differences between FeMoco and FeVco

Fe N2ase: Oxidized and Turnover States 5.2.3. The Iron Protein of Alternative Nitrogenases 6. The Assembly of [Fe4S4] Clusters on NifU 6.3. Synthesis of the 8Fe Precursor of FeMoco on NifB 6.4. Processing of the L-cluster by NifEN 6.5. P-Cluster Maturation and the Role of NifH 6.6. Transfer of FeMoco to MoFe: Yet Another. Differences in Cofactor Maturation for VFe and FeFe 6.9. Corresponding Author Authors Notes Biographies Acknowledgments Abbreviations Used References

INTRODUCTION
SPECTROSCOPIC METHODS
Special Topic
Vibrational Spectroscopy
Optical Spectroscopy
X-ray Spectroscopy
Theory and its Correlation with Spectroscopy
CHARACTERIZING N2ASES THROUGH MODEL CHEMISTRY
F-Cluster
P-Clusters
FeMoco
Mo N2ASE
FeP and the F-Cluster
The P-Cluster
Photoinduced Reductive Elimination from
Beyond E4
Acetylene Reduction
Propargyl Alcohol Reduction
4.10. CO Reduction
4.11. Cyanide
ALTERNATIVE N2ASES
V N2ase
Fe N2ase
W N2ase
The Iron Protein of Alternative Nitrogenases
CLUSTER BIOSYNTHESIS
Overview
Synthesis of the 8Fe Precursor of FeMoco on NifB
Processing of the L-cluster by NifEN
P-Cluster Maturation and the Role of NifH
Transfer of FeMoco to MoFe
Spectroscopic Properties of Additional Maturases
Differences in Cofactor Maturation for VFe and FeFe
SUMMARY AND OUTLOOK
Findings
Comparison of Redox and EPR Properties of the Molybdenum
Full Text
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