• Haem peroxidases (or heme peroxidases) are haem-containing enzymes that use hydrogen peroxide as the electron acceptor to catalyse a number of oxidative reactions. (wikipedia.org)
  • Collectively, the data show that all three members of the class I heme peroxidases can support radical formation on the distal tryptophan and that the reactivity of this radical can be controlled either by the protein structure or by the nature of the compound I intermediate. (bris.ac.uk)
  • One oxidizing equivalent resides on iron, giving the oxyferryl intermediate, and in many peroxidases the porphyrin (R) is oxidized to the porphyrin pi-cation radical (R'). Compound I then oxidizes an organic substrate to give a substrate radical and Compound II, which can then oxidize a second substrate molecule. (wikipedia.org)
  • 2007) Biochemistry 46, 2174-2180] that reaction of APX with peroxide leads, over long time scales, to formation of a covalent link with the distal tryptophan (Trp41) in a mechanism that proceeds through initial formation of a compound I species bearing a porphyrin π-cation radical followed by radical formation on Trp41, as implicated in the KatG enzymes. (bris.ac.uk)
  • Formation of such a covalent link in CcP has never been reported, and we proposed that this could be because compound I in CcP uses Trp191 instead of a porphyrin π-cation radical. (bris.ac.uk)
  • To test this, we have examined the reactivity of the W191F variant of CcP with H 2 O 2 , in which formation of a porphyrin π-cation radical occurs. (bris.ac.uk)
  • Fe3+ + H2O + oxidized substrate In this mechanism, the enzyme reacts with one equivalent of H2O2 to give [Fe4+=O]R' (compound I). This is a two-electron oxidation/reduction reaction in which H2O2 is reduced to water, and the enzyme is oxidized. (wikipedia.org)
  • Fe3+ + H2O + oxidized substrate In this mechanism, the enzyme reacts with one equivalent of H2O2 to give [Fe4+=O]R' (compound I). This is a two-electron oxidation/reduction reaction in which H2O2 is reduced to water, and the enzyme is oxidized. (wikipedia.org)
  • The initial step for both catalytic processes is the heterolytic reduction of H2O2 to H2O, giving rise to a two-electron oxidation of the ferric enzyme to a ferryl-porphyrin π cation radical intermediate, compound I (i.e. (auburn.edu)
  • To complete the catalase reaction, compound I returns to the ferric state by oxidation of another H2O2 to form O2 and H2O. (auburn.edu)
  • However, the peroxidase reaction is completed by the subsequent reduction of compound I to compound II (i.e. (auburn.edu)
  • Conversely, catalase activity can sustain high concentrations of H2O2 without the enzyme inactivation. (auburn.edu)
  • Based on this mechanism, both activities should be mutually antagonistic and peroxidatic electron donors should inhibit the catalase activity. (auburn.edu)
  • Clearly, the catalase mechanism and the interrelationship between the catalase and peroxidase functions of KatG are much more complex than has been previously appreciated, and pH plays an important factor in both activities. (auburn.edu)
  • This is far less than the amount expected for normal peroxidatic turnover where two equivalents of oxidized donor is anticipated for every equivalent of H2O2 consumed. (auburn.edu)
  • intermediate dominated during electron donor-stimulated catalase activity of MtKatG, and this intermediate converted directly to the ferric state upon depletion of H2O2. (auburn.edu)
  • Catalase activity is optimal near neutral pH (i.e., pH ~ 7.5), whereas peroxidase activity is optimal under acidic conditions (i.e., pH ~ 4.5) and requires an exogenous electron donor. (auburn.edu)