INHIBITION OF ENZYMATIC INDOLE-3-ACETIC-ACID OXIDATION BY PHENOLS

The influence of natural and unnatural phenolic inhibitors on peroxidase-catalysed oxidation of indole-acetic acid (IAA) was investigated using chemiluminescent and spectrophotometric methods. The threshold effect under inhibition was observed for all studied phenolic compounds. The IAA oxidation stopped only if the concentration of inhibitor was more than some threshold value. The spontaneous reinitiation of the stopped reaction was also investigated. The system of chemical reactions, required for the description of threshold effect under inhibition and spontaneous reinitiation of stopped reaction, was proposed. Moreover, the effect of H2O2 on the inhibited IAA oxidation was studied. It was found that addition of H2O2 caused a reinitiation of stopped reaction. Threshold effect was observed for the reinitiation. The reinitiation took place only when the concentration of H2O2 was more than a threshold value which depended on the inhibitor concentration. The total quantity of H2O2 required for the reaction reinitiation on the addition of H2O2 a little at a time was more than that on addition by a single large portion. The results obtained are discussed in terms of free-radical chain reaction of enzymatic IAA oxidation.