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 myoglobins reconstituted with synthesized iron(III) meso-substituted porphyrins have 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 C(alpha) atom of Arg45 in each crystal was displaced by 2.7 angstrom 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 porphyrin was estimated from the refined anisotropic temperature factors of its atoms, which showed that the root-mean-square amplitude of the vibration about the normal to the porphyrin plane was significantly larger than the globin's movement.