Mössbauer and EPR studies of iron-containing proteins
Schulz, Charles Emil
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https://hdl.handle.net/2142/25547
Description
Title
Mössbauer and EPR studies of iron-containing proteins
Author(s)
Schulz, Charles Emil
Issue Date
1979
Doctoral Committee Chair(s)
Debrunner, Peter G.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Mossbauer
iron-containing proteins
rubredoxin
horseradish peroxidase
Electron Paramagnetic Resonance (EPR)
Language
en
Abstract
"We have studied the iron-sulfur protein rubredoxin (Rd) and the heme protein horseradish peroxidase (HRP) using Mossbauer spectroscopy (MS) and electron paramagnetic resonance (EPR). Both methods are sensitive probes of the electronic structure of the iron at the active site of the protein. In all cases studied, the observed spectra can be explained in terms of a spin Hamiltonian, which describes the ground electronic spin multiplet and the electron-nuclear interactions. In general, spin-phonon coupling must be taken into account explicitly, and in one case spin-spin interaction of the iron with a radical has been observed. Model parameters are deduced from comparison of experimental spectra with theoretical predictions. We have developed simulation algorithms for Mossbauer and for EPR spectra. For the latter, line shapes are calculated by a ""g-strain"" model which assumes a distribution of the spin Hamiltonian parameters.
Both oxidized and reduced Rd have fine structure parameters of rhombic symmetry. has an exceptionally slow spin-lattice relaxation, which is dominated by direct processes up. to 150K. We have studied HRP in the native state and as the reaction intermediates, compounds (1) and (11). The spin Hamiltonian of the high-spin ferric form of the native HRP has nearly axial symmetry and, as deduced from the temperature dependence of the spin fluctuation rate, an
exceptionally large fine structure splitting, D=20K. 80th (1) and (II) have the heme iron in the intermediate spin 8=1 ferryl state, with similar fine structure and hyperfine parameters. We demonstrate that the extra oxidizing equivalent of (I) is a radical, which couples weakly to the iron spin. Model calculations assuming a porphyrin cation yield the proper order of magnitude for dipole-dipole coupling, but an unexpectedly broad distribution in the exchange interaction is required to fit the EPR data."
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