The Fe-V Cofactor of Vanadium Nitrogenase Contains an Interstitial Carbon Atom

The first direct evidence is provided for the presence of an interstitial carbide in the FeV cofactor of Azotobacter vinelandii vanadium nitrogenase. As for our identification of the central carbide in the FeMo cofactor, we employed Fe Kβ valence‐to‐core X‐ray emission spectroscopy and density functional theory calculations, and herein report the highly similar spectra of both variants of the cofactor‐containing protein. The identification of an analogous carbide, and thus an atomically homologous active site in vanadium nitrogenase, highlights the importance and influence of both the interstitial carbide and the identity of the heteroatom on the electronic structure and catalytic activity of the enzyme. Stuck in the middle: The first experimental evidence for the presence of an interstitial carbide in the active‐site FeV cofactor in vanadium nitrogenase is presented. The presence of the carbide was identified using valence‐to‐core X‐ray emission spectroscopy. The carbide is analogous to that of the FeMo cofactor of molybdenum nitrogenase, and is only the second reported carbide ligand in biology.