Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors

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• 作者：Tomokazu Shibata ; Yuki Kanai ; Ryu Nishimura ; Liyang Xu ; Yuki Moritaka ; Akihiro Suzuki ; Saburo Neya ; Mikio Nakamura ; Yasuhiko Yamamoto
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：December 5, 2016
• 年：2016
• 卷：55
• 期：23
• 页码：12128-12136
• 全文大小：534K
• ISSN：1520-510X

文摘

We introduced trifluoromethyl (CF₃) group(s) as heme side chain(s) of sperm whale myoglobin (Mb) in order to characterize the electronic nature of heme Fe(II) in deoxy Mb using ¹⁹F NMR spectroscopy. On the basis of the anti-Curie behavior of CF₃ signals, we found that the deoxy Mb is in thermal equilibrium between the ⁵B₂, (d_xy)²(d_xz)(d_yz)(d_z²)(d_x²–y²), and ⁵E, (d_xy)(d_xz)²(d_yz)(d_z²)(d_x²–y²), states of the heme Fe(II), i.e., ⁵B₂ ⇆ ⁵E. Analysis of the curvature in Curie plots has yielded for the first time ΔH and ΔS values of ∼−20 kJ mol^–1 and ∼−60 J K^–1 mol^–1, respectively, for the thermal equilibrium. Thus, the ⁵E state is slightly dominant over the ⁵B₂ one at 25 °C. These findings provide not only valuable information about the ground state electronic structure of the high-spin heme Fe(II) in deoxy native Mb but also an important clue for elucidating the mechanism responsible for acceleration of the spin-forbidden oxygenation of the protein.