title: X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin.
abstract: We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.
authors.affiliation: Physical Biosciences, LBNL, Cyclotron Road 1, Berkeley, California 94720, USA. funk@lbl.gov
authors.forename: Tobias
authors.initials: T
authors.lastname: Funk
authors.forename: Pierre
authors.initials: P
authors.lastname: Kennepohl
authors.forename: Angel J
authors.initials: AJ
authors.lastname: Di Bilio
authors.forename: William A
authors.initials: WA
authors.lastname: Wehbi
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Young
authors.forename: Stephan
authors.initials: S
authors.lastname: Friedrich
authors.forename: Elke
authors.initials: E
authors.lastname: Arenholz
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Cramer
mesh_terms: D001400:Azurin / Q000737:chemistry*; D002942:Circular Dichroism / Q000379:methods*; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D008024:Ligands; D008280:Magnetics; D008958:Models, Molecular; D008968:Molecular Conformation; D009532:Nickel / Q000737:chemistry*; D011550:Pseudomonas aeruginosa / Q000737:chemistry*; D014965:X-Rays
chemical_list: D008024:Ligands; D001400:Azurin; D003300:Copper; D009532:Nickel