Dynamics of hemoglobin investigated by Mössbauer spectroscopy.

Abstract Mossbauer Spectra of 57Fe enriched horse hemoglobin and sperm whale myoglobin were measured in the temperature range from 80 K to 260 K. An analysis of the temperature dependence of the recoiless fraction (the Lamb-Mossbauer factor) shows it to be sensitive to conformational fluctuations which affect the mean square displacement of the iron. We have found that the protein conformation has a dramatic effect on these measurements. For hemoglobin greater conformational fluctuations at lower temperatures are observed for carbonmonoxyhemoglobin in the liganded conformation than for deoxyhemoglobin in the unliganded conformation. On the other hand, the Lamb-Mossbauer factor is insensitive to the binding of ligands to myoglobin and shows conformational fluctuations similar to deoxyhemoglobin even in the liganded state. It is also shown that a reversible complex with the distal histidine is formed in frozen deoxyhemoglobin solutions above 200 K where the Lamb-Mossbauer factor shows the excitation of new ...