Indole‐3‐methanol as an intermediate in the oxidation of indole‐3‐acetic acid by peroxidase

During oxidation of indole‐3‐acetic acid catalyzed by horseradish peroxidase, indole‐3‐aldehyde and 3‐hydroxymethayloxindole cease to be produced a few minutes after initiation of the reaction even though IAA is still being consumed. At the same time an increased accumulation of indole‐3‐methanol is observed and the ratio of oxygen to indole‐3‐acetic acid consumed becomes less than unity. Indole‐3‐niethanol can be a substrate for horseradish peroxidase provided that H2O2 is present. In this reaction, indole‐3‐aldehyde but not 3‐hydroxymethyloxindole is formed. H2O2 is not merely an activating agent for the enzyme but also a true oxidant because it is consumed stoichiometrically (1 mol of H2O2 per mol of indole‐3‐methanol) and the reaction is independent of the presence of oxygen. Indole‐3‐methanol is proposed as an intermediate in the process of oxidation of indole‐3‐acetic acid into indole‐3‐al‐denyde, the second step of which requires peroxide as an oxidant.