Conformational substate distribution in low spin ferric myoglobin as studied by electron paramagnetic resonance

Electron paramagnetic resonance of low spin ferric myoglobin frozen solutions have been analyzed in terms of Gaussian distributions of the tetragonal and rhombic splitting parameters Δ andV. These distributions have been interpreted as arising from the frozen disorder resulting from the presence of a conformational substate distribution of the protein molecules. The parameters characterizing the Δ andV distributions, extracted by computer simulation, are shown to be affected by the solvent composition and by the cooling rate at which the samples are submitted. The results are discussed in relation to the behaviour of the high spin ferric myoglobin samples in the same conditions.