Partial Purification and Characterization of Indol-3-Ylacetylglucosemyo-Inositol Indol-3-Ylacetyltransferase (Indoleacetic Acid-Inositol Synthase) 1

A procedure is described for the purification of the enzyme indol-3-ylacetylglucose: myo -inositol indol-3-ylacetyltransferase (IAA- myo -inositol synthase). This enzyme catalyzes the transfer of indol-3-ylacetate from 1-0-indol-3-ylacetyl-β- d -glucose to myo -inositol to form indol-3-ylacetyl- myo -inositol and glucose. A hexokinase or glucose oxidase based assay system is described. The enzyme has been purified approximately 16,000-fold, has an isoelectric point of pH 6.1 and yields three catalytically inactive bands upon acrylamide gel electrophoresis of the native protein. The enzyme shows maximum transferase activity with myo -inositol but shows some transferase activity with scyllo-inositol and myo -inosose-2. No transfer of IAA occurs with myo -inositol- d -galactopyranose, cyclohexanol, mannitol, or glycerol as acyl acceptor. The affinity of the enzyme for 1-0-indol-3-ylacetyl-β- d -glucose is, K m = 30 micromolar, and for myo -inositol is, K m = 4 millimolar. The enzyme does not catalyze the exchange incorporation of glucose into IAA-glucose indicating the reaction mechanism involves binding of IAA glucose to the enzyme with subsequent hydrolytic cleavage of the acyl moiety by the hydroxyl of myo -inositol to form IAA myo -inositol ester.