Kinetics and thermodynamics of the reaction of peroxides with manganese-reconstituted horseradish peroxidase: a stopped-flow transient kinetic investigation

Abstract

The reaction of manganese-reconstituted horseradish peroxidase (MnHRP) with peroxides of different nature has been investigated by stopped-flow kinetics in order to understand the nature of the active site of the enzyme, the differences in the mechanism of the formation of MnHRP–I with different peroxides and possible resolution of the intermediate(s) involved. The reaction of m-ClC₆H₄CO₃H with MnHRP shows that only the unionised species of the peracid reacts. tert-Butyl hydroperoxide reacted with MnHRP, although it does not with native HRP. The reaction shows saturation kinetics at room temperature for the formation of MnHRP–I at high concentrations of Bu^tO₂H. This observation provides direct evidence for a reversible binding step of the enzyme and peroxide before the product formation. The thermodynamic parameters for the formation of MnHRP–I are similar to those for HRP–I formation, indicating that the mode of formation of both peroxide compounds may be similar.