Destruction of indoleacetic acid : IV. Kinetics of enzymic oxidation

Abstract

Kinetics of enzymic oxidation of indoleacetic acid (IAA) are interpreted as indicating that the reaction has an autocatalytic, cyclical mechanism involving unstable intermediates whose formation and disappearance are important in determining the over-all reaction rate. The kinetics do not support the idea that IAA oxidation occurs mainly by reaction with Mn+3, nor that the reaction is an electron transfer from IAA to O2 catalyzed by a pcroxidase-H2O2-Mn+2 complex, nor that Mn is essential to the reaction. H2O2 is probably not a major reaction intermediate. One-electron oxidation of IAA by peroxidase giving a free radical, followed by spontaneous reaction of the radical with oxygen to give a peroxy oxidant which can reoxidize the peroxidase to a peroxide complex, appears to be a likely mechanism.