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  • Title: Energy distributions at the high-spin ferric sites in myoglobin crystals.
    Author: Fiamingo FG, Brill AS, Hampton DA, Thorkildsen R.
    Journal: Biophys J; 1989 Jan; 55(1):67-77. PubMed ID: 2539208.
    Abstract:
    The orientation and temperature dependence (4.2-2.5 K) of electron paramagnetic resonance (EPR) power saturation and spin-lattice relaxation rate, and the orientation dependence of signal linewidth, were measured in single crystals of the aquo complex of ferric sperm whale skeletal muscle myoglobin. The spin-packet linewidth was found to be temperature independent and to vary by a factor of seven within the heme plane. An analysis is presented which enables one to arrive at (a) hyperfine component line-widths and, from the in-plane angular variation of the latter, at (b) the widths of distributions in energy differences between low-lying electronic levels and (c) the angular spread in the in-plane principal g-directions. The values of the energy level distributions in crystals obtained from the measurements and analysis reported here are compared with those obtained by a different method for the same protein complex in frozen solution. The spread in the rhombic energy splitting is significantly greater in solution than in the crystal.
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