DISTRIBUTION OF THE IRON HEME DISPLACEMENT AS RESULTING FROM MYOGLOBIN CONFORMATIONAL SUBSTATES - AN AOM APPROACH TO THE INTERPRETATION OF THE EPR-SPECTRA

The electron paramagnetic resonance (EPR) low-temperature spectra of high spin ferric myoglobin samples in different solvent composition have been analyzed in terms of a distribution of the energy differences DELTA1 and DELTA2 for the iron low-lying electronic states. The widths of these distributions, which are found to be dependent on the solvent composition, have been correlated to the presence of a frozen ensemble of conformational substrates. A dedicated analysis based on the angular overlap method (AOM) has allowed us to work out a quantitative relationship between the DELTA1 and DELTA2 distributions and the spread of the iron heme displacement; this being a structural parameter relevant for the biological functionality of the protein. The observed dependence of the iron-heme displacement distribution on the solvent composition is discussed.