STRUCTURAL FLUCTUATIONS OF MYOGLOBIN FROM NORMAL-MODES, MOSSBAUER, RAMAN, AND ABSORPTION-SPECTROSCOPY

A normal-mode analysis of carbon monoxymyoglobin (MbCO) and deoxymyogl obin (Mb) with 170 water molecules is performed for Fe-54 and Fe-57. A projection is defined that extracts iron out-of-plane vibrational mod es and is used to calculate spectra that can be compared with those fr om resonance Raman scattering. The calculated spectra and the isotopic shift Fe-57 versus Fe-54 agree with the experimental data, At low tem peratures the average mean square fluctuations (MSFs) of the protein b ackbone atoms agree with molecular dynamics simulation, Below 180 K th e MSFs of the heme iron agree with the data from Mossbauer spectroscop y. The MSFs of the iron atom relative to the heme are an order of magn itude smaller than the total MSFs of the iron atom. They agree with th e data from optical absorption spectroscopy. Thus the MSFs of the iron atom as measured by Mossbauer spectroscopy can be used to probe the o verall motion of the heme within the protein matrix, whereas the Gauss ian thermal line broadening of the Soret band and the resonance Raman bands can be used to detect local intramolecular iron-porphyrin motion s.