Publications Details
Calcium-Dependent Conformation of a Heme and Fingerprint Peptide of the Di-Heme Cytochrome c Peroxidase from Paracoccus Pantotrophus
The structural changes in the heme macrocycle and substituents caused by binding of Ca{sup 2+} to the diheme cytochrome c peroxidase from Paracoccuspantotrophus were clarified by resonance Raman spectroscopy of the inactive filly oxidized form of the enzyme. The changes in the macrocycle vibrational modes are consistent with a Ca{sup 2+}-dependent increase in the out-of-plane distortion of the low-potential heme, the proposed peroxidatic heme. Most of the increase in out-of-plane distortion occurs when the high affinity site I is occupied, but a small further increase in distortion occurs when site II is also occupied by Ca{sup 2+}or Mg{sup 2+}. This increase in the heme distortion also explains the red shift in the Soret absorption band that occurs upon Ca{sup 2+} binding. Changes also occur in the low frequency substituent modes of the heme, indicating that a structural change in the covalently attached fingerprint pentapeptide of the LP heme occurs upon CM{sup 2+} binding to site I. These structural changes, possibly enhanced in the semi-reduced form of the enzyme, may lead to loss of the sixth ligand at the peroxidatic heme and activation of the enzyme.