Structure and dynamics of photodissociated myoglobin.

The low frequency resonance Raman spectra of photodissociated carbon monoxy myoglobin at cryogenic temperatures (4-77K) differ from those of deoxy myoglobin. From these data it was inferred that a 4K a photoproduct is generated with an expanded heme core, an iron atom that has not relaxed to its full out-of- plane position, and an iron-histidine bond which is perpendicular to the heme plane. As the temperature is increased toward 77K the core contracts and the iron takes on its full out- of-plane position. Full relaxation occurs at temperatures greater than 77K. Energy minimization calculations show that subsequent to photodissociation the carbon monoxide molecule moves away from the iron atom to a distance of about 4Angstroms.