Destruction of indoleacetic acid. IV. Kinetics of enzymic oxidation.

Kinetics of enzymic oxidation of indoleacetic acid (ISA) are interpreted as indicating that the reaction has an autocatalytic, cyclical mechanism invol\-ing unst,ablc intermcdiatcs whose formation and disappearance are important in determining the over-all reaction rate. The kinetics do not supporl the idea that IAA oxidation occurs mainly by reaction with Mnt3, nor that the reaction is an electron transfer from IAA to 0, catalyzed by a pcroxidase-HsOrMn+’ complex, nor t,hat Mn is essential to the reaction. H,O, is probably not a major reaction intermediate. One-electron oxidation of IAA by peroxidasc giving a free radical, followed by spontaneous reaction of the radical with oxygen to give a peroxy oxidant which can rcoxitlize the peroxidase to a peroxide complex, appears to be a likcl\mechanism.