TEMPERATURE-DEPENDENCE OF THE G=6 EPR LINEWIDTH IN HIGH-SPIN FEIII MYOGLOBIN SAMPLES

The temperature dependence of the g = 6 line of high spin FeIII aqueou s mixed water-glycerol myoglobin samples has been investigated by EPR spectroscopy. The trend with the temperature of the linewidth has been analyzed by taking into account both a temperature-independent contri bution from the frozen structural heterogeneity (conformational substa te distribution) and the relaxation processes. The temperature-depende nt line broadening process due to the spin-lattice relaxation has been singled out by simulation of the experimental data and put into relat ionship to the density of the vibrational states. The effect on the vi brational modes of the protein-solvent system, as induced by the addit ion of large amount of the glass-making solvent, glycerol, is discusse d.