Some limitation in the use of the I- method for measuring the peroxidase activity from bovine thyroid gland.

Studied for measuring the peroxidase activity from thyroid gland have usually been achieved on the basis of the H2O2 oxidation of I- to I3- catalyzed by peroxidase. The activity assay has been found to depend on several factors such as the relative order of reagent addition, protein content of the enzyme preparation, presence of detergent and the pH of the reaction medium. At below 7.0 pH, the contribution of the non-enzymic transformation of I- to total activity became quite significant, to the extent that at below 6.5 pH, the chemical reaction predominates over the enzymic one. At values above 7.0 pH, a very rapid decomposition of the product was observed. Guaiacol oxidation has been considered to be a more reliable method than the iodide one, especially when the substrate concentration and temperature vary, and when the activity of relatively rich in protein samples, as well as of some other substances that might interfere with the I3- formation, are going to be measured.