title: Electron-paramagnetic-resonance and magnetic-circular-dichroism studies of the binding of cyanide and thiols to the thiols to the iron-molybdenum cofactor from Klebsiella pneumoniae nitrogenase.
abstract: FeMoco, a low-M(r) metal cluster of probable composition Fe7MoS9 complexed with homocitrate, has been extracted with N-methylformamide from the MoFe protein of the nitrogenase enzyme from Klebsiella pneumoniae. The binding of cyanide and thiols to the FeMoco cluster in its paramagnetic S = 3/2 oxidation level has been studied by low-temperature e.p.r. and magnetic-circular-dichroism (m.c.d.) spectroscopies. Cyanide binds to isolated FeMoco at more than one site, and causes changes in the g values form g = 4.6, 3.2, 2.0 to g = 4.29, 3.82, 2.02 E.p.r. competition studies indicate that one cyanide can be displaced by thiolate from one type of site. The form of the low-temperature m.c.d. spectrum is little changed by ligand binding, thus the basic cluster structure remains intact. However, when benzenethiol is bound, a new intense band (lambda 387 nm) is observed, indicating the generation of an increased ligand-to-cluster charge-transfer interaction.
authors.affiliation: School of Chemical Sciences, University of East Anglia, Norwich U.K.
authors.forename: A J
authors.initials: AJ
authors.lastname: Richards
authors.forename: D J
authors.initials: DJ
authors.lastname: Lowe
authors.forename: R L
authors.initials: RL
authors.lastname: Richards
authors.forename: A J
authors.initials: AJ
authors.lastname: Thomson
authors.forename: B E
authors.initials: BE
authors.lastname: Smith
mesh_terms: D002942:Circular Dichroism; D003486:Cyanides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D008280:Magnetics; D008983:Molybdoferredoxin / Q000737:chemistry*; D009591:Nitrogenase / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D003486:Cyanides; D008983:Molybdoferredoxin; D013438:Sulfhydryl Compounds; D009591:Nitrogenase