title: Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors.
abstract: 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 using19F NMR spectroscopy. On the basis of the anti-Curie behavior of CF3signals, we found that the deoxy Mb is in thermal equilibrium between the5B2, (dxy)2(dxz)(dyz)(dz2)(dx2-y2), and5E, (dxy)(dxz)2(dyz)(dz2)(dx2-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-1and ∼-60 J K-1mol-1, respectively, for the thermal equilibrium. Thus, the5E state is slightly dominant over the5B2one 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.
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kanai
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Ryu
authors.initials: R
authors.lastname: Nishimura
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Liyang
authors.initials: L
authors.lastname: Xu
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Moritaka
authors.affiliation: Department of Materials Engineering, Nagaoka National College of Technology , Nagaoka 940-8532, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Suzuki
authors.affiliation: Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University , Chuoh-Inohana, Chiba 260-8675, Japan.
authors.forename: Saburo
authors.initials: S
authors.lastname: Neya
authors.affiliation: Department of Chemistry, Faculty of Science, Toho University , Funabashi, Chiba 274-8510, Japan.
authors.forename: Mikio
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Chemistry, University of Tsukuba , Tsukuba 305-8571, Japan.|Life Science Center of Tsukuba Advanced Research Alliance, University of Tsukuba , Tsukuba 305-8577, Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Yamamoto
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009211:Myoglobin / Q000737:chemistry*; D013696:Temperature
chemical_list: D056831:Coordination Complexes; D005296:Ferrous Compounds; D008024:Ligands; D009211:Myoglobin; C055547:deoxymyoglobin; D006418:Heme