Compounds I of Catalase and Horse Radis

Two-electron oxidation of cobaltous octa- ethylporphyrin (Co(II)(Et),P) yields a stable 7r-cation radical (Co(III)(Et)sP)2', the optical spectrum of which exhibits spectral changes dependent upon the nature of the counterion. Comparison of these spectra with those of Compounds I of horseradish peroxidase and catalase leads us to propose that these Compounds I contain a 7r-cation radical of the heme prosthetic group. This proposal ex- plains the oxidation level, optical spectra, and stability of the primary compounds without recourse to properties such as stoichiometric mixtures of special porphyrins, stable Fe(V) porphyrins, or unique conformers of heme porphyrins. Explanations are advanced to account for the missing electron spin resonance signal of Compound I of horseradish peroxidase.