Reactivity of the Repair of Iron Centers Protein YtfE toward NO, and the Activation of Oxygen and Nitrite Molecules by Non-heme Diiron Complex

• Main Authors: Hsieh, Chang-Chih, 謝長志
• Other Authors: Liaw, Wen-Feng
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/11933382989294252408

博士 === 國立清華大學 === 化學系 === 104 === The protein structure of YtfE was solved by X-ray crystallography, and the detailed coordination environment of the diiron core was characterized and confirmed by EPR and 17O-labeling ESEEM measurements. Each iron in the diiron core was coordinated with one vacancy, two histidines, two bridged carboxylates of glutamates and one oxo-bridging in the distorted octahedron geometry. Two tunnels in YtfE able to transport small molecules such as nitric oxide, water and nitrous oxide were found. The experiments of affinity and reactivity of nitric oxide with reduced and mix-valence YtfE demonstrate that YtfE has moderate affinity for nitric oxide which can be reduced to nitrous oxide in the nitrosylated ([FeIII(NO)-FeIII(NO)]) YtfE state by adding reducing agent. The result suggests that YtfE acts as nitric oxide trapping-scavenger to protect itself and keep the primitive redox state for the repair function. Oxygen and nitrite molecules can be activated to form water and nitric oxide respectively by complex 1 ((LNHS)2Fe)2, and the reactions were studied by NMR, EPR, UV-vis, X-ray, ESI-MS, IR and DFT calculation. Both reactions do not need to add any extra proton source or the trigger for OAT. The intramolecular hydrogen bond interaction is considered to play an important role in the reactions by the results of DFT calculation. The formation of water and the oxidation of the organic ligand (LNHS)2 can be observed from in situ NMR experiment for oxygen activation, and the important intermediate (LNHS)2Fe-μ-1,2-O2-Fe(LNHS)2 (C) was confirmed by P-oxidation and hydride-transfer experiments. The proposed mechanism for oxygen activation by complex 1 mimics the catalytic mechanism of CcO well. Complex [(LNHS)2Fe(NO)2]- was generated in nitrite activation by complex 1 via an intermediate [(LNHS)2Fe-κ1-NO2]- (F), and [(LNS)Fe(NO)] or [(LNS)Fe(NO)]2 is the degradation product of [(LNHS)2Fe(NO)2]- in DMSO. Both complex 3 [Na][(LNS)2Fe] and [(LNHS)2Fe(NO)2]- are considered as the products in the nitrite reduction similar to the results of the early report by Fout’s group.