A crystallographic study of deoxy cobalt (II) mesoporphyrin IX myoglobin.

The crystal structures of acid metmyoglobin and deoxy cobalt(II)mesoporphyrin IX myoglobin were compared by a difference Fourier analysis at 2.5 A resolution. No large differences in protein conformation were observed. The greatest density of structural differences was found in the heme region. There was a loss of the histidine-bound sulfate ion and of the metal-bound water molecule, as well as a shift in the position of the prosthetic group with associated changes in the adjacent globin. The structural changes resulting from the substitution of ethyl for the vinyl side chains of the porphyrin were clearly observed. There was also a suggestion of a conformational change of the porphyrin ring. It was not clear whether there was any change of the metal position relative to the porphyrin plane or proximal histidine.