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Science 11 June 2004:
Vol. 304. no. 5677, pp. 1653 - 1656
DOI: 10.1126/science.1096897
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Reports

Oxoiron(IV) in Chloroperoxidase Compound II Is Basic: Implications for P450 Chemistry

Michael T. Green,1* John H. Dawson,2 Harry B. Gray3

With the use of x-ray absorption spectroscopy, we have found that the Fe-O bond in chloroperoxidase compound II (CPO-II) is much longer than expected for an oxoiron(IV) (ferryl) unit; notably, the experimentally determined bond length of 1.82(1) Å accords closely with density functional calculations on a protonated ferryl (FeIV-OH, 1.81 Å). The basicity of the CPO-II ferryl [pKa > 8.2 (where Ka is the acid dissociation constant)] is attributable to strong electron donation by the axial thiolate. We suggest that the CPO-II protonated ferryl is a good model for the rebound intermediate in the P450 oxygenation cycle;with elevated pKa values after one-electron reduction, thiolate-ligated ferryl radicals are competent to oxygenate saturated hydrocarbons at potentials that can be tolerated by folded polypeptide hosts.

1 Department of Chemistry, Pennsylvania State University, PA 16802, USA.
2 Department of Chemistry and Biochemistry, University of South Carolina, SC 29208, USA.
3 Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.

* To whom correspondence should be addressed. E-mail: mtg10{at}psu.edu

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