An electron paramagnetic resonance study of conformational substate distribution in high spin heme-proteins

The electron paramagnetic resonance spectra of high spin ferric horse myoglobin and human hemoglobin have been analyzed by computer simulation in terms of a distribution of the metal ion crystal field energies Δ₁ and Δ₂. The widths of these distributions have been put into relation 0 to the distribution of the conformational substates which may be sampled by the biomolecules during their physiological activity and become eventually arrested at low temperature. These distributions are found to be dependent upon both the solvent used and the cooling history to which the samples were submitted. The results are discussed in connection with the physical analogies displayed by these biomolecules and the glassy systems in general.