Brown H M, Purves W K
J Biol Chem. 1976 Feb 25;251(4):907-13.
In a continuing study of the biosynthetic pathway and regulatory mechanisms governing indole-3-acetic acid (auxin) formation, we report the isolation and initial characterization of three distinct indole-3-acetaldehyde reductases from cucumber seedlings. These enzymes catalyze the reduction of indole-3-acetaldehyde to indole-3-ethanol with the concomitant oxidation of NAD(P)H to NAD(P)+. Two of the reductases are specific for NADPH as second substrate, while the third is specific for NADH. The enzymes show a strong specificity for indoleacetaldehyde, with apparent Km values of 73mum, 130mum, and 400mum being calculated for the two NADPH-specific reductases and the NADH-specific reductase, respectively. Under no conditions of substrate concentration, incubation time, or assay method could the reverse reaction be observed. Chromatography on a calibrated Sephadex gel column led to estimated molecualr weights of 52,000 and 17,000 for the NADPH-specific reductases, while a value of 33,000 was obtained for the NADH-specific reductase. Both NADPH-specific reductases showed a pH optimum of 5.2 with a secondary optimum at 7.0, and both enzymes were activated by increasing ionic strength. The NADH-specific reductase showed a pH optimum of 7.0 with a secondary optimum at 6.1 and was slightly inhibited by increasing ionic strength.
在一项关于吲哚 - 3 - 乙酸（生长素）生物合成途径及调控机制的持续研究中，我们报告了从黄瓜幼苗中分离出三种不同的吲哚 - 3 - 乙醛还原酶并对其进行初步表征。这些酶催化吲哚 - 3 - 乙醛还原为吲哚 - 3 - 乙醇，同时将NAD(P)H氧化为NAD(P)+。其中两种还原酶对NADPH作为第二底物具有特异性，而第三种对NADH具有特异性。这些酶对吲哚乙醛表现出很强的特异性，两种NADPH特异性还原酶和NADH特异性还原酶的表观Km值分别计算为73μM、130μM和400μM。在任何底物浓度、孵育时间或测定方法的条件下均未观察到逆反应。在校准的Sephadex凝胶柱上进行色谱分析得出，NADPH特异性还原酶的估计分子量为52,000和17,000，而NADH特异性还原酶的值为33,000。两种NADPH特异性还原酶的最适pH值均为5.2，在7.0处有一个次要最适值，并且两种酶都通过增加离子强度而被激活。NADH特异性还原酶的最适pH值为7.0，在6.1处有一个次要最适值，并且随着离子强度的增加略有抑制。
