The Peroxidase Activity of Deuterohemin

The reaction of hydrogen peroxide with deuterohemin and the reaction of the products with peroxidase substrates in neutral aqueous solution have been investigated. Qualitative observations indicate that, prior to oxidative degradation of the porphyrin ring system, a peroxidatic hemeperoxide complex is formed which can react with hydrogen donors to regenerate free deuterohemin. Quantitative data support this conclusion and show that this complex formation can account for the peroxidase activity of deuterohemin. The kinetics of formation of this complex and its reaction with peroxidase substrates have been studied and indicate that the principal difference between the catalytic mechanisms of deuterohemin and peroxidase is the very much more rapid rate of formation of the primary active complex in peroxidase. The overall rate of conversion of the primary active complex to the free catalyst is approximately the same in both enzyme and model systems, although in the latter case no intermediate analogous to compound II of peroxidase is formed.The mechanism of action of peroxidases and the nature of their active peroxide complexes is discussed in the light of these findings.