Iron(IV)hydroxide pKa and the role of thiolate ligation in C-H bond activation by cytochrome P450

Timothy H. Yosca, Jonathan Rittle, Courtney M. Krest, Elizabeth L. Onderko, Alexey Silakov, Julio C. Calixto, Rachel K. Behan, Michael T. Green

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Abstract

Cytochrome P450 enzymes activate oxygen at heme iron centers to oxidize relatively inert substrate carbon-hydrogen bonds. Cysteine thiolate coordination to iron is posited to increase the pKa (where Ka is the acid dissociation constant) of compound II, an iron(IV)hydroxide complex, correspondingly lowering the one-electron reduction potential of compound I, the active catalytic intermediate, and decreasing the driving force for deleterious auto-oxidation of tyrosine and tryptophan residues in the enzyme's framework. Here, we report on the preparation of an iron(IV)hydroxide complex in a P450 enzyme (CYP158) in ≥90% yield. Using rapid mixing technologies in conjunction with Mössbauer, ultraviolet/visible, and x-ray absorption spectroscopies, we determine a pKa value for this compound of 11.9. Marcus theory analysis indicates that this elevated pKa results in a >10,000-fold reduction in the rate constant for oxidations of the protein framework, making these processes noncompetitive with substrate oxidation.

Original languageEnglish (US)
Pages (from-to)825-829
Number of pages5
JournalScience
Volume342
Issue number6160
DOIs
StatePublished - Jan 1 2013

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All Science Journal Classification (ASJC) codes

  • General

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Yosca, T. H., Rittle, J., Krest, C. M., Onderko, E. L., Silakov, A., Calixto, J. C., Behan, R. K., & Green, M. T. (2013). Iron(IV)hydroxide pKa and the role of thiolate ligation in C-H bond activation by cytochrome P450. Science, 342(6160), 825-829. https://doi.org/10.1126/science.1244373