An electron paramagnetic resonance study of the high and low spin forms of chloroperoxidase.

摘要: The electron paramagnetic resonance spectra of chloroperoxidase, a heme protein isolated from the mold Caldariomyces fumago, and its complexes with variety substrates inhibitors have been investigated. At liquid helium temperatures, EPR spectrum native chloroperoxidase prepared at pH 1.5 is essentially that high spin ferric iron, while frozen solutions enzyme 5 exhibit low spectrum. 3.0, both forms are observed. These results indicate exists as pH-dependent equilibrium mixture temperature, increasing above causes transition form having g values 7.64,4.29, 1.78 to near 2.61, 2.26, 1.83. binding such ligands Br-, I-, F- in shift favors addition cyanide, azide, imidazole, 2-mercaptoethanol shifts almost completely towards forms. chloride has no major effect on spin-low equilibrium. Analysis for shows it exhibits an extremely large rhombic distortion (-20%). F-, C1-, I- not only alters but also rhombicity, indicating halide perturbs symmetry well. An analysis indicates electronic environment iron bears closer resemblance cytochrome P-450 than various nitrogen-, oxygen-, carbon-ligated myoglobin, hemoglobin, or horseradish peroxidase. However,