The destruction of indoleacetic acid. III. Relationships between peroxidase action and indoleacetic acid oxidation

Abstract

The indoleacetic acid (IAA)-oxidizing enzyme preparation from Omphalia flavida exhibits peroxidase activity on pyrogallol with an optimum at pH 3.5-3.7, like that for the IAA-oxidizing activity. It shows no polyphenolase activity. Peroxidase and IAA-oxidizing activities run parallel both during thermal inactivation and in course of purification of the enzyme, and are therefore considered to be due to one enzyme.IAA inhibits peroxidation of pyrogallol by the enzyme, 50% inhibition being obtained at about 7 x 10-6 M. The inhibition appears to be specific to substrates of the oxygen-consuming activity of the enzyme. IAA destruction is inhibited at the same time, even though an excess of H2O2 is present. IAA is not destroyed at an appreciable rate in the absence of O2, even if substrate amounts of H2O2 are present, whereas pyrogallol peroxidation is not influenced by the absence of O2. IAA oxidation is light-reversibly inhibited by CO; the inhibition is affected by O2 concentration. A possible interpretation of the results is that the reaction depends upon a free-radical mechanism involving the formation of ferrous peroxidase.