Kinetics and mechanism of catalase action. Formation of the intermediate complex

The kinetics of formation of the intermediate complex between catalase and H₂O₂ has been reexamined. It has been shown that the kinetics consists of a rapid and of a subsequent slow phase. At the maximum of the transient decrement of the optical absorption, the system was found to be in a terminal state with regard to the rapid phase. On this basis, the formation curve of the intermediate complex was calculated. From the parameters of the curve the maximal saturation of catalase hematins (from horse erythrocytes) by H₂O₂ is 35%. The absolute spectrum of the intermediate complex was established. The variation of the previously calculated rate constant of formation of the intermediate complex was shown to be due to the inapplicability of the pre-steady-state approximation to the rate data. By applying a more general approach and by the use of a computer, the individual rate constants of the peroxidatic scheme were calculated (relevant to micromolar solutions of catalase) k₁ = (3.0 ± 0.2) × 10⁶ M^?1 sec^?1k₄ = (5.6 ± 0.3) × 10⁶ M^?1 sec^?1 These values are 2.2 times higher in a nanomolar solution.