Cryoreduction of the NO-adduct of taurine:alpha-ketoglutarate dioxygenase (TauD) yields an elusive {FeNO}(8) species.
The Fe(II)- and alpha-ketoglutarate (alphaKG)-dependent enzymes are a functionally and mechanistically diverse group of mononuclear nonheme-iron enzymes that activate dioxygen to couple the decarboxylation of alphaKG, which yields succinate and CO(2), 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 O(2) adduct, which is a {FeO(2)}(8) species in the notation introduced by Enemark and Feltham. Here, we report spectroscopic and computational studies on the stable NO-adduct of taurine:alphaKG 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 gamma-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.
Ye
Shengfa
S
Institute of Physical and Theoretical Chemistry, Universität Bonn, D-53115 Bonn, Germany.
Price
John C
JC
Barr
Eric W
EW
Green
Michael T
MT
Bollinger
J Martin
JM
Krebs
Carsten
C
Neese
Frank
F
D002245:Carbon Dioxide / Q000138:chemical synthesis / Q000737:chemistry; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008280:Magnetics; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000378:metabolism; D008968:Molecular Conformation; D009569:Nitric Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D015204:Spectroscopy, Mossbauer; D013237:Stereoisomerism; D019802:Succinic Acid / Q000138:chemical synthesis / Q000737:chemistry
D005290:Ferric Compounds; D005296:Ferrous Compounds; D002245:Carbon Dioxide; D009569:Nitric Oxide; D019802:Succinic Acid; D007501:Iron; D006899:Mixed Function Oxygenases; C433064:taurine-alpha-ketoglutarate dioxygenase