Cryogenic stabilization of myoglobin photoproducts.

The low frequency resonance Raman spectra of photodissociated carbon monoxy myoglobin at cryogenic temperatures (4-77K) differ from those of deoxy myoglobin. Intensity differences occur in several low frequency porphyrin modes and intensity and frequency differences occur in the iron-histidine stretching mode. This mode appears at about 225 cm(-1) in deoxy myoglobin. At the lowest temperature studied, ~ 4K, the frequency of the iron-histidine stretching mode in the photoproduct is ~ 233 cm(-1) and the intensity is very low. When the temperature of the photoproduct is increased, the intensity of the mode increases but its frequency is unchanged. The differences between the photoproduct and the deoxy preparation persist to 77K, the highest temperatures studied and are independent of whether samples are frozen in phosphate buffer or a 50/50 ethylene glycol/phosphate buffer mixture.