Peroxidase-like activities of iron(III)-porphyrins: Kinetics of the reduction of a peroxidatically active derivative of deuteroferriheme by phenols

The kinetics of reduction of a peroxidatically active intermediate (formed by reaction of deuteroferriheme with hydrogen peroxide) by phenol and a series of substituted phenols have been studied by stopped-flow spectrophotometry. The complex effects of varying heme concentration have been interpreted in terms of the formation of a dimeric form of the intermediate by reaction of monomeric intermediate with unoxidized ferriheme monomer. Both the relative reactivity of phenols towards the two forms of the intermediate and the rate constants for reduction of intermediate are markedly influenced by phenol substituents. Effects of pH suggest that phenolate anions are the reactive forms of the reductants. Rate constants for the monomeric intermediate reactions (k_DFH) are related to those (k_HRP) for the corresponding reductions of horseradish peroxidase Compound I by the following relation: log k_DFH = 1.53 log k_HRP ? 3.74.