Resonance Raman detection of structural dynamics at the active site in hemoglobin

The iron-histidine stretching mode in deoxyhemoglobin displays a large change in frequency and width upon lowering the temperature from 300 to 10 K. The temperature dependence of the data indicates the presence of dynamic processes. The dynamics of this mode in frozen hemoglobins can be qualitatively and quantitatively described as a vibrational dephasing via anharmonic coupling to other vibrations of the heme-imidazole system. The effects that occur at the melting transition in the low frequency modes cannot be quantitatively addressed at this point but may be indicative of the introduction of additional degrees of freedom predicated on protein influences that reflect differences in protein quaternary structure.