Time-resolved and cw Raman Studies of Conformational Heterogeneity and Relaxation in Photodissociated Liganded Myoglobins at Cryogenic Temperatures

Time resolved and cw resonance Raman studies comparing deoxymyoglobin and photodissociated liganded myoglobins over a wide range of temperatures (1.6-230K) have been used to address several fundamental issues. In addition to deoxy and carboxy sperm whale myoglobin, other myoglobins (elephant and tuna) and ligands (N-butyl isocyanide) were used to expose the sensitivity of specific heme Raman bands to distal and peripheral influences. On the basis of such studies, it is concluded that the shifted core marker band (v2) in the deoxy photoproduct is not due to a non-fully out of heme plane iron but is derived instead from ligand induced changes in the distal heme packet. A comparison of the cw and time resolved (10 ns) spectra at 160K indicates that the cryogenically trapped intermediates of photodissociated COMb may not be relevant in the higher temperature reaction. A potentially significant influence of the photodissociated ligand upon both structural relaxation and heme structure is indicated from a comparison of the temperature dependent changes in the spectra of the photoproduct derived from COMb and N-butyl isocyanide Mb. Studies of hysteresis and Raman hole burning effects are in progress. These studies are being used to examine the dynamics associated with conformational heterogeneity especially in the regime of the "glass transition" at equivalent to 180-200K.