Irreversible inactivation of lactoperoxidase in the course of iodide oxidation

Inhibition of peroxidase-catalyzed iodination by thioamides: experimental and theoretical study of the antithyroid activity of thioamides

“…Iodide anion (I À ) is easily oxidized by H 2 O 2 in a 2e À transfer reaction either non-enzymatically or enzymatically in the presence of peroxidase, according to the following equation: 27 …”

“…17 Also I À is needed in excess since below a concentration of 10 mM no I 3 À or I 2 production could be detected spectroscopically. 17,27 Hence, a 100% production of I 3 À is equivalent to a concentration of 50 mM of I 3 À which is the maximum amount of H 2 O 2 consumed in this reaction. The amount of I 3 À present was calculated from the spectra using the fact that the molar ratio between H 2 O 2 degradation and I 3 À formation was 1 : 1 (eqn (2)).…”

“…Symmetry transformations used to generate equivalent atoms: It should be noticed that the use of the mixture of CH 2 Cl 2 and MeOH solvents help in protecting the iron porphyrin 30 and in maintaining the tri-iodide mixture equilibrium (3) thus preventing the extinction coefficient from varying. 27 The assay system contained KI = 10 mM (160 ml of 0.125 M KI), [H 2 O 2 ] = 50 mM (10 ml of 30% w/v HO), [FeTPPCl] = 5 mM (10 ml of 10 À3 M FeTPPCl), [L] = 5 mM (10 ml of 10 À3 M thioamide). The volume was adjusted to the total of 2 ml in the cell.…”

“…The amount of I 3 À present was calculated from the spectra using the fact that the molar ratio between H 2 O 2 degradation and I 3 À formation was 1 : 1 (eqn ( 2)). 17,27 Hence, a 100% production of I 3 À is equivalent to a concentration of 50 mM of I 3 À which is the maximum amount of H 2 O 2 consumed in this reaction. The percent inhibition was calculated from the difference between the reference (98%) and the percent of I 3 À formed in the presence of the thioamide ligands.…”