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Journal Article

Cryoreduction of the NO-Adduct of Taurine:α-Ketoglutarate Dioxygenase (TauD) Yields an Elusive {FeNO}8 Species

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Ye, S., Price, J. C., Barr, E. W., Green, M. T., Bollinger Jr., J. M., Krebs, C., et al. (2010). Cryoreduction of the NO-Adduct of Taurine:α-Ketoglutarate Dioxygenase (TauD) Yields an Elusive {FeNO}8 Species. Journal of the American Chemical Society, 132(13), 4739-4751. doi:10.1021/ja909715g.

Cite as: http://hdl.handle.net/21.11116/0000-0008-0FCD-2
The Fe(II)- and α-ketoglutarate (αKG)-dependent enzymes are a functionally and mechanistically diverse group of mononuclear nonheme-iron enzymes that activate dioxygen to couple the decarboxylation of αKG, which yields succinate and CO2, to the oxidation of an aliphatic C−H bond of their substrates. Their mechanisms have been studied in detail by a combination of kinetic, spectroscopic, and computational methods. Two reaction intermediates have been trapped and characterized for several members of this enzyme family. The first intermediate is the C−H-cleaving Fe(IV)−oxo complex, which exhibits a large deuterium kinetic isotope effect on its decay. The second intermediate is a Fe(II):product complex. Reaction intermediates proposed to occur before the Fe(IV)−oxo intermediate do not accumulate and therefore cannot be characterized experimentally. One of these intermediates is the initial O2 adduct, which is a {FeO2}8 species in the notation introduced by Enemark and Feltham. Here, we report spectroscopic and computational studies on the stable NO-adduct of taurine:αKG dioxygenase (TauD), termed TauD−{FeNO}7, and its one-electron reduced form, TauD−{FeNO}8. The latter is isoelectronic with the proposed O2 adduct and was generated by low-temperature γ-irradiation of TauD−{FeNO}7. To our knowledge, TauD−{FeNO}8 is the first paramagnetic {FeNO}8 complex. The detailed analysis of experimental and computational results shows that TauD−{FeNO}8 has a triplet ground state. This has mechanistic implications that are discussed in this Article. Annealing of the triplet {FeNO}8 species presumably leads to an equally elusive {FeHNO}8 complex with a quintet ground state.