A Nuclear Resonance Vibrational Spectroscopic Study of Oxy Myoglobins Reconstituted with Chemically Modified Heme Cofactors: Insights into the Fe-O 2 Bonding and Internal Dynamics of the Protein.

The molecular mechanism of O-2 binding to hemoglobin (Hb) and myoglobin (Mb) is a long-standing issue in the field of bioinorganic and biophysical chemistry. The nature of Fe-O-2 bond in oxy Hb and Mb had been extensively investigated by resonance Raman spectroscopy, which assigned the Fe-O-2 stretching bands at similar to 570 cm(-1). However, resonance Raman assignment of the vibrational mode had been elusive due to the spectroscopic selection rule and to the limited information available about the ground-state molecular structure. Thus, nuclear resonance vibrational spectroscopy was applied to oxy Mbs reconstituted with Fe-57-labeled native heme cofactor and two chemically modified ones. This advanced spectroscopy in conjunction with DFT analyses gave new insights into the nature of the Fe-O-2 bond of oxy heme by revealing the effect of heme peripheral substitutions on the vibrational dynamics of heme Fe atom, where the main Fe-O-2 stretching band of the native protein was characterized at similar to 420 cm(-1).