Studies on Cytochrome c Peroxidase

Electron paramagnetic resonance absorption spectra cytochrome c peroxidase at 77°K exhibit well defined signal at g = ∼6.0, 4.3 (weak), 2.7, 2.2, ∼2.0 (weak), and 1. On the formation of Complex ES, by adding hydroperoxide to the enzyme, these electron paramagnetic resonance signals of the enzyme almost completely disappear and replaced by an intense narrow signal of a free radical type at g = 2.00. The spin concentration of this free radical is estimated to be about 1 eq to enzyme hematin unit. It is speculated that one of the 2 oxidizing equivalents of Complex ES may te retained in the form of a stable and reversible free radical of aromatic amino acid residue of the enzyme protein and the other in the hematin prosthetic group of the enzyme.