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.
描述了纯化
吲哚-3-基乙酰
葡萄糖:肌醇
吲哚-3-基乙酰转移酶(
IAA-肌醇合成酶)的过程。这种酶催化 1-0-indol-3-ylacetyl-β-d-glucose 与肌醇之间的
吲哚-3-ylacetate 转移,形成
吲哚-3-ylacetyl-myo-肌醇和
葡萄糖。描述了一种基于
己糖激酶或
葡萄糖氧化酶的检测系统。该酶已纯化约 16,000 倍,等电点为 pH 6.1,在对原生蛋白进行
丙烯酰胺凝胶电泳时会产生三条无催化活性的条带。该酶在肌醇中显示出最大的转移酶活性,但在酰肌醇和
肌苷-2 中也显示出一定的转移酶活性。以肌醇-半
乳糖、
环己醇、
甘露醇或
甘油为酰基受体时,
IAA 不会发生转移。该酶对 1-0-indol-3-ylacetyl-β-d-glucose 的亲和力为 K m = 30 微摩尔,对肌醇的亲和力为 K m = 4 毫摩尔。该酶不能催化
葡萄糖与
IAA-
葡萄糖的交换结合,这表明反应机理是
IAA 葡萄糖与该酶结合,随后酰基被肌醇的羟基
水解裂解,形成
IAA 肌醇酯。