title: The interstitial atom of the nitrogenase FeMo-cofactor: ENDOR and ESEEM evidence that it is not a nitrogen.
abstract: X-ray crystallographic study of the nitrogenase MoFe protein revealed electron density from an atom (denoted X) inside the active-site metal cluster, the [MoFe7S9:homocitrate] FeMo-cofactor. The electron density associated with X is consistent with a single N, O, or C atom. We now have tested whether X is an N or not by comparing the Q-band ENDOR and ESEEM signals from resting-state (S = 3/2) MoFe protein and NMF-extracted FeMo-co from bacteria grown with either 14N or 15N as the exclusive N source. All of the 14N or 15N signals associated with the protein are lost upon extraction of the FeMo-co. We interpret this as strong evidence that X is not an N.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Tran-Chin
authors.initials: TC
authors.lastname: Yang
authors.forename: Nathan K
authors.initials: NK
authors.lastname: Maeser
authors.forename: Mikhail
authors.initials: M
authors.lastname: Laryukhin
authors.forename: Hong-In
authors.initials: HI
authors.lastname: Lee
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Dean
authors.forename: Lance C
authors.initials: LC
authors.lastname: Seefeldt
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
mesh_terms: D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D008983:Molybdoferredoxin / Q000737:chemistry*; D009591:Nitrogenase / Q000737:chemistry*
chemical_list: D008983:Molybdoferredoxin; D009591:Nitrogenase