Indoleacetic Acid Oxidases in Resting Cereal Grains

Peroxidases oxidizing indoleacetic acid (IAA) are present in the resting grains of barley, rye and wheat. The grains also contain small molecular inhibitors of the enzymes. A partly purified preparation of barley seed proteins was shown to contain at least two IAA oxidases about pI 5 and pI 10, mol. weight 30,000 and with a pH optimum 5.1–5.7. The enzymes require Mn²⁺, 2,4-dichlorophenol and orthophosphate for the maximum activity. Attempts to separate IAA oxidase and peroxidase activities of the enzymes were unsuccessful.