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

Shengfa Ye, John C. Price, Eric W. Barr, Michael T. Green, J. Martin Bollinger, Carsten Krebs, Frank Neese

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Abstract

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 O 2 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.

Original languageEnglish (US)
Pages (from-to)4739-4751
Number of pages13
JournalJournal of the American Chemical Society
Volume132
Issue number13
DOIs
StatePublished - Apr 7 2010

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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