Spectroscopic studies of the anaerobic enzyme-substrate complex of catechol 1,2-dioxygenase

Geoff P. Horsman, Andrew Jirasek, Frédéric H. Vaillancourt, Christopher J. Barbosa, Andrzej A. Jarzecki, Changliang Xu, Yasmina Mekmouche, Thomas G. Spiro, John D. Lipscomb, Michael W. Blades, Robin F.B. Turner, Lindsay D. Eltis

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


The basis of the respective regiospecificities of intradiol and extradiol dioxygenase is poorly understood and may be linked to the protonation state of the bidentate-bound catechol in the enzyme/substrate complex. Previous ultraviolet resonance Raman (UVRR) and UV-visible (UV-vis) difference spectroscopic studies demonstrated that, in extradiol dioxygenases, the catechol is bound to the Fe(II) as a monoanion. In this study, we use the same approaches to demonstrate that, in catechol 1,2-dioxygenase (C12O), an intradiol enzyme, the catechol binds to the Fe(III) as a dianion. Specifically, features at 290 nm and 1550 cm-1 in the UV-vis and UVRR difference spectra, respectively, are assigned to dianionic catechol based on spectra of the model compound, ferric tris(catecholate). The UVRR spectroscopic band assignments are corroborated by density functional theory (DFT) calculations. In addition, negative features at 240 nm in UV-vis difference spectra and at 1600, 1210, and 1175 cm-1 in UVRR difference spectra match those of a tyrosinate model compound, consistent with protonation of the axial tyrosinate ligand when it is displaced from the ferric ion coordination sphere upon substrate binding. The DFT calculations ascribe the asymmetry of the bound dianionic substrate to the trans donor effect of an equatorially ligated tyrosinate ligand. In addition, the computations suggest that trans donation from the tyrosinate ligand may facilitate charge transfer from the substrate to yield the iron-bound semiquinone transition state, which is capable of reacting with dioxygen. In illustrating the importance of ligand trans effects in a biological system, the current study demonstrates the power of combining difference UVRR and optical spectroscopies to probe metal ligation in solution.

Original languageEnglish (US)
Pages (from-to)16882-16891
Number of pages10
JournalJournal of the American Chemical Society
Issue number48
StatePublished - Dec 7 2005


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