The reaction of hemin with H₂O₂

The kinetics of formation of the dominant intermediate (C_II) formed between hemin and H₂O₂ has been studied by the stopped‐flow method. C_II is preceded by a precursor (C_I) for which a steady state is established at an early stage of the reaction. The formation of C_I from hemin and H₂O₂ causes only a marginal change in the optical absorbance (A). The transition C_I°C_II is accompanied by a substantial decrease of A in the Soret region. Relevant rate constants (or combinations of them) and the molar absorption coefficients of the intermediates at 400 nm have been determined. The absorption spectrum of C_II in the Soret region has been evaluated. Aspects of the catalysis of decomposition of H₂O₂ by hemin in relation to the Fe³⁺ ion and catalase are discussed.