Abstract
The chemical substitution of ferrous protoporphyrin IX with cobaltous protoporphyrin IX in myoglobin (Mb) and hemoglobin (Hb) has allowed for the detailed investigation of modes of interaction among molecular oxygen, the prothetic group, and the apoprotein moiety in these oxygen carrying hemoproteins.
We have compared the ligand orientation of oxy meso-CoMb with that of oxy proto-CoMb by single crystal EPR spectroscopy at ambient and cryogenic temperatures. Single orientation was found at ambient temperature, but upon freezing two unequivalent orientations of O-O axis were found in both cobalt myoglobin single crystals.
On the otherhand, two different ν(O-O) stretching vibrations were observed in oxy CoMb by resonance Raman spectroscopy at ambient temperature. We have demonstrated that metal-ligand geometry in these Co (II) complexes in unfrozen fluid and frozen solid states is altered by chemical modification at 2, 4-porphyrin peripheral groups.
