The 1.13-Å structure of iron-free cytochrome c peroxidase

The iron-free cytochrome c peroxidase (CCP) crystal structure has been determined to 1.13 angstrom and compared with the 1.2-angstrom ferric-CCP structure. Quite unexpectedly, removal of the iron has no effect on porphyrin geometry and distortion, indicating that protein porphyrin interactions and not iron coordination or formation of the axial His - Fe bond determines porphyrin conformation. However, there are changes in solvent structure in the distal pocket, which lead to changes in the distal His52 acid - base catalyst. The observed ability of His52 to move in response to small changes in solvent structure is very likely important for its role as a catalyst in assisting in the heterolytic fission of the peroxide O - O bond.