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Published June 11, 2004 | public
Journal Article

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

Abstract

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 (Fe^(IV)-OH, 1.81 Å). The basicity of the CPO-II ferryl [pK_a > 8.2 (where K_a 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 pK_a 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.

Additional Information

© 2004 American Association for the Advancement of Science. 18 February 2004; Accepted 21 April 2004. We thank M. Bollinger, I. Dmochowski, J. Labinger, M. Machczynski, M. McGuirl, A. Tezcan, and J. Winkler for helpful discussions; G. George, I. Pickering, M. Latimer, B. Butler, A. Soo Hoo, S. Debeer George, D. Durkin, and other SSRL staff members for assistance with XAS measurements; and L. Hager for a CPO sample used in the initial experiments. Supported by NIH (GM26730 to J.H.D. and DK19038 to H.B.G.), NSF, and the Arnold and Mabel Beckman Foundation.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023