Studies on Cytochrome c Peroxidase

The reaction of ferrimyoglobin with H2O2 was investigated by a combination of spectrophotometric and electron paramagnetic resonance measurements and enzymic assay of of hydroperoxide by the cytochrome c peroxidase system. On the addition of an excess of H2O2 to ferrimyoglobin, approximately 1.5 moles of H2O2 were consumed per mole of the ferrimyoglobin peroxide compound formed, and the remaining H2O2 was slowly decomposed in the presence of the peroxide compound. George and Irvine's conclusion was confirmed that the peroxide compound retains only 1 oxidizing equivalent per hemin unit. Available evidence was consistent with the reaction mechanism of Equations 1, 2, and 3 (see text). Transient free radicals were formed not only during the active formation of the peroxide compound but also during the decomposition of hydroperoxide in the presence of the peroxide compound. Rate constants associated with the peroxide compound were compared with those of Complex ES (the peroxide compound) of cytochrome c peroxidase.