The Crystal Structures of Cyanide Metmyoglobins Reconstituted with Iron(III) Complexes of Porphyrin, 5,10,15,20-Tetramethylporphyrin, and 5,10,15,20-Tetraethylporphyrin

The structures of three mimic myoglobinsreconstituted with synthesized iron(III) meso-substituted porphyrinshave been studied by X-ray crystallography. Although the overall structure of each globin was the same as that of the native, apart from a few terminal residues, the Cα atom of Arg45 in each crystal was displaced by 2.7 A from that in the native. This large displacement opens a channel for the ligand penetration, formed by His64, Thr67, Val68, and heme. The movement of each porphyrinwas estimated from the refined anisotropic temperature factors of its atoms, which showed that the root-mean-squaresamplitude of the vibration about the normal to the porphyrinplane was significantly larger than the globin’s movement.