Chemistry and Biology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario K1A OC6, Canada.
Plant Physiol. 1972 Jun;49(6):1012-8. doi: 10.1104/pp.49.6.1012.
The naturally occurring coumarin, scopoletin, has been found to modify horseradish peroxidase rapidly to give a stable, spectroscopically distinguishable form of the enzyme. Peroxidase treated with scopoletin is less active in reactions with molecular oxygen and indole-3-acetic acid. Kinetic data for the degradation of this growth regulator were obtained with a continuously monitored fluorometric procedure. Lineweaver-Burk plots of the reciprocal rate of degradation against the reciprocal substrate concentration were markedly curved in the presence of the inhibitor, scopoletin. Excess indole-3-acetate restored the scopoletin-treated enzyme to a reactive state. In the presence of molecular oxygen, concentrations of indole-3-acetic acid which were at least 10-fold greater than the inhibitor concentration led to the rapid oxidation of the coumarin and converted peroxidase to compound III as expected from previous studies. This form of the enzyme is the catalytically active species in the oxidative degradation of the growth regulator. The kinetically preferential reaction of scopoletin or related coumarins with peroxidase and the suppression of indole-3-acetic acid degradation may provide a possible control mechanism over the oxidative degradation of indole-3-acetate by this plant enzyme.
自然界中存在的香豆素，东莨菪内酯，已被发现可迅速修饰辣根过氧化物酶，形成一种稳定的、在光谱上可区分的酶形式。用东莨菪内酯处理过的过氧化物酶在与分子氧和吲哚-3-乙酸的反应中活性较低。通过连续监测荧光的程序获得了这种生长调节剂降解的动力学数据。在抑制剂东莨菪内酯存在下，降解的倒数速率与底物浓度的倒数的Lineweaver-Burk 图明显弯曲。过量的吲哚-3-乙酸将东莨菪内酯处理过的酶恢复到反应状态。在分子氧存在下，至少比抑制剂浓度大 10 倍的吲哚-3-乙酸浓度导致香豆素迅速氧化，并如先前的研究预期的那样将过氧化物酶转化为化合物 III。这种形式的酶是生长调节剂氧化降解中的催化活性物质。东莨菪内酯或相关香豆素与过氧化物酶的动力学优先反应以及对吲哚-3-乙酸降解的抑制作用，可能为植物酶对吲哚-3-乙酸的氧化降解提供了一种可能的控制机制。
