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The two-state issue in the mixed-valence binuclear cu-a center in cytochrome c oxidase and n2o reductase

Academic Article
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Overview

authors

  • Gorelsky, S. I.
  • Xie, X. J.
  • Chen, Y.
  • Fee, James
  • Solomon, E. I.

publication date

  • December 2006

journal

  • Journal of the American Chemical Society  Journal

abstract

  • For the CuA site in the protein, sigmau* and piu are the ground and lowest energy excited-states, respectively. EPR data on CuA proteins show a low g parallel value of 2.19 which derives from spin-orbital coupling between sigmau* and piu which requires an energy gap between sigmau* and piu of 3000-4500 cm-1. On the other hand, from paramagnetic NMR studies, it has been observed that the first excited-state is thermally accessible and the energy gap between the ground state and the thermally accessible state is approximately 350 cm-1. This study addressed this apparent discrepancy and evaluated the roles of the two electronic states, sigmau* and piu, in electron transfer (ET) of CuA. The potential energy surface calculations show that both NMR and EPR results are consistent with the electronic/geometric structure of CuA. The anti-Curie behavior observed in paramagnetic NMR studies of CuA results from the thermal equilibrium between the sigmau* and piu states which are at very close energies in their respective equilibrium geometries. Alternatively, the EPR g-value analysis involves the sigmau* ground state in the geometry with a short dCu-Cu where the piu state is a Frank-Condon excited-state with the energy of 3200 cm-1. The protein environment plays a role in maintaining CuA in the sigmau* state as a lowest-energy state with the lowest reorganization energy and high-covalent coupling to the Cys and His ligands for efficient intra- and intermolecular ET with a low-driving force.

subject areas

  • Copper
  • Electron Transport Complex IV
  • Models, Chemical
  • Oxidation-Reduction
  • Oxidoreductases
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Identity

International Standard Serial Number (ISSN)

  • 0002-7863

Digital Object Identifier (DOI)

  • 10.1021/ja067583i

PubMed ID

  • 17177365
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Additional Document Info

start page

  • 16452

end page

  • 16453

volume

  • 128

issue

  • 51

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