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

The influence of natural and unnatural phenolic inhibitors on peroxida se-catalysed oxidation of indole-acetic acid (IAA) was investigated us ing chemiluminescent and spectrophotometric methods. The threshold eff ect under inhibition was observed for all studied phenolic compounds. The IAA oxidation stopped only if the concentration of inhibitor was m ore than some threshold value. The spontaneous reinitiation of the sto pped 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 thresh old value which depended on the inhibitor concentration. The total qua ntity of H2O2 required for the reaction reinitiation on the addition o f H2O2 a little at a time was more than that on addition by a single l arge portion. The results obtained are discussed in terms of free-radi cal chain reaction of enzymatic IAA oxidation.