title: Energy distributions at the high-spin ferric sites in myoglobin crystals.
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.
authors.affiliation: Department of Physics and Biophysics Program, University of Virginia, Charlottesville 22901.
authors.forename: F G
authors.initials: FG
authors.lastname: Fiamingo
authors.forename: A S
authors.initials: AS
authors.lastname: Brill
authors.forename: D A
authors.initials: DA
authors.lastname: Hampton
authors.forename: R
authors.initials: R
authors.lastname: Thorkildsen
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000378:metabolism; D007501:Iron; D008433:Mathematics; D008872:Microwaves; D008962:Models, Theoretical; D009211:Myoglobin / Q000378:metabolism*; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D009211:Myoglobin; D006418:Heme; D007501:Iron