The relationship between oxidase activity, peroxidase activity, hydrogen peroxide, and phenolic compounds in the degradation of indole-3-acetic acid in vitro.

The peroxidase catalyzed degradation of indole-3-acetic acid (IAA) results in the formation of indole-3-methanol (IM) in the presence of phenolic compounds or in 3-hydroxymethyloxindole (HMOx) in their absence. Apparently the phenols compote with a methyleneindolenine intermediate for H2O2 which is produced by oxidase action preceding the peroxidase action in the course of IAA degradation. The substitution pattern of various phenolic compounds tested strongly effects the rate of the reaction. However, this substitution pattern does not appear to effect the type of the reaction or the products formed. We suggest that the function of the "oxindole pathway" is to detoxify excess H2O2 in the absence of phenolic cosubstrates. The results lead to a number of interesting aspects of IAA biochemistry and to the proposal of a new reaction scheme for the peroxidase catalyzed degradation of IAA.