title: Horseradish peroxidase-catalyzed conversion of iodine to iodide in presence of EDTA and H2O2.
abstract: EDTA (4 mM) blocks the oxidation of iodide to I-3 (increase of extinction at 353 nm) by H2O2 catalyzed by horseradish peroxidase, which is reversed by the addition of an equimolar concentration of Zn2+. Addition of suboptimal concentration of EDTA (2 mM) not only decreases the rate of forward reaction of I-3 formation but also causes loss of extinction of the same when I-3 is generated. The loss of extinction of I-3 is proportional to the enzyme concentration and is blocked by azide, the inhibitor of the peroxidase. EDTA also causes bleaching of nonenzymatically formed I-3 (from iodide and H2O2) only in the presence of horseradish peroxidase, and the effect is reversed by the equimolar concentration of Zn2+. Both the bleaching of I-3 by EDTA and reversal of EDTA effect by Zn2+ are sensitive to azide. The decrease of extinction of I-3 (formed by dissolving iodine in KI solution) is dependent on EDTA, H2O2, and horseradish peroxidase. Molecular iodine is also bleached but at a slower rate than I-3. Evidence is presented to show that this bleaching of I-3 is due to enzymatic conversion of I-3 to iodide in presence of EDTA and H2O2 and this involves pseudocatalatic degradation of H2O2 to O2.
mesh_terms: D004492:Edetic Acid / Q000494:pharmacology*; D006735:Horseradish Peroxidase / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007454:Iodides / Q000032:analysis; D007455:Iodine / Q000378:metabolism*; D007700:Kinetics; D010544:Peroxidases / Q000378:metabolism*
chemical_list: D007454:Iodides; D007455:Iodine; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D010544:Peroxidases