X-ray Magnetic Circular Dichroism of Pseudomonas aeruginosa Nickel(II) Azurin
X-ray Magnetic Circular Dichroism of Pseudomonas aeruginosa Nickel(II) Azurin
Received May 19, 2003
Web Release Date: April 20, 2004
Tobias Funk,* Pierre Kennepohl, Angel J. Di Bilio, William A. Wehbi, Anthony T. Young, Stephan Friedrich, Elke Arenholz, Harry B. Gray,* and Stephen P. Cramer*
J. Am. Chem. Soc.
ACS Publications
Copyright ? 2004 American Chemical Society
Contribution from the Physical Biosciences, LBNL, Cyclotron Road 1, Berkeley, California 94720; Beckman Institute, California Institute of Technology, Pasadena, California 91125; Advanced Light Source, LBNL, Cyclotron Road 1, Berkeley, California 94720; Advanced Detector Group, LLNL, Livermore, California 94550; and Department of Applied Science, University of California at Davis, One Shields Avenue, Davis, California 95616
funk@lbl.gov; hbgray@caltech.edu; SPCramer@ucdavis.edu
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 L3-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) B. Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3dx2-y2 and 3dz2 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 3dx2-y2 having much greater ligand character.
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