The Role of 2,4-Dichlorophenol in the Destruction of Indoleacetic Acid by Peroxidase.

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Abstract
Commercial dehydrated horseradish has been found to have a high peroxidase activity as measured by the oxidation of pyrogallol and other standard substrates, but it failed to effect the destruction of IAA (indole-3-acetic acid). On the addition of DCP (2,4 dichlorophenol) the peroxidase system destroyed IAA at rates equal to those previously reported with the peroxidase system. It is thus demonstrated that the DCP cofactor, previously shown to be required in an IAA oxidase is effective in the peroxidase portion of the enzyme system. Aqueous extracts of the leaves of Xanthium pensylvanicum were found to have a high peroxidase activity on the usual peroxidase substrates but failed to destroy IAA. The addition of the Xanthium peroxidase extract to horseradish peroxidase resulted in an inhibition of IAA destruction by the horseradish system. Partial purification of the Xanthium peroxidase removed the inhibitor, but the Xanthium enzyme failed to destroy IAA, even on addition of DCP, manganese and boiled horseradish enzyme. It is suggested that the peroxidases from the two sources differ in substrate specificity.