Proposed Model for the Peroxidase-Catalyzed Oxidation of Indole-3-acetic Acid in the Presence of the Inhibitor Ferulic Acid 1

Linear increments in ferulic acid concentration produce logarithmic increases in the ferulic acid-induced lag periods prior to the peroxidase-catalyzed oxidation of indole-3-acetic acid in a system containing 2,4-dichlorophenol and MnCl(2) in acetate buffer at pH 5.6. Maintaining the ratio of indole-3-acetic acid to ferulic acid constant at 100 while linearly raising the ferulic acid concentration results in linear increases in the lag period. Both indole-3-acetic acid and ferulic acid are substrates of horseradish peroxidase in the presence of H(2)O(2), and indole-3-acetic acid competitively inhibits the oxidation of ferulic acid. A model for the enzymatic oxidation of indole-3-acetic acid catalyzed by peroxidase is proposed.