PHOSPHORIBOSYL ANTHRANILATE ISOMERASE CATALYZES A REVERSIBLE AMADORI REACTION
PHOSPHORIBOSYL ANTHRANILATE ISOMERASE CATALYZES A REVERSIBLE AMADORI REACTION
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DOI：
10.1021/bi00016a014
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发表时间：
1995-04-25
期刊：
影响因子：
2.9
通讯作者：
KIRSCHNER, K
中科院分区：
文献类型：
--
作者：
HOMMEL, U;EBERHARD, M;KIRSCHNER, K
稳态和瞬态动力学的数据表明，从大肠杆菌的天然双功能酶的功能磷酸核糖邻氨基苯甲酸异构酶结构域具有类似的性质，其人工切除的结构域。来自酿酒酵母（Saccharomyces cerevisiae）的天然单功能酶具有显著高于右箭头（cat）的（k）值和显著高于右箭头/K-M（PRA）的（k）值。磷酸核糖基氨基苯甲酸酯的单一周转的主要产物是荧光的，但它缓慢异构化为非荧光的稳定产物。后者是吲哚甘油磷酸合酶的感受态底物，吲哚甘油磷酸合酶催化色氨酸生物合成的后续步骤。异构化的特点是由一个独立的磷酸核糖邻氨基苯甲酸异构酶的单指数衰减。由于荧光，初级产品和nonfluorescent，稳定的产品，烯醇和酮化合物，分别暂定分配，色氨酸的生物合成似乎是由未催化的烯醇/酮互变异构的速率限制。一个正式的动力学机制的磷酸核糖基邻氨基苯甲酸异构酶催化的反应提出的是一致的磷酸核糖基邻氨基苯甲酸异构酶的三种变体的酶和配体结合特性相结合。
Data from steady state and transient kinetics show that the functional phosphoribosyl anthranilate isomerase domain of the naturally bifunctional enzyme from Escherichia coli has properties similar to those of its artificially excised domain. The naturally monofunctional enzyme from Saccharomyces cerevisiae has significantly higher values of both (k) over right arrow(cat) and (k) over right arrow/K-M(PRA). The primary product of a single turnover of phosphoribosylanthranilate is fluorescent, but it slowly isomerizes to the nonfluorescent stable product. The latter is the competent substrate of indoleglycerol phosphate synthase, which catalyzes the subsequent step of tryptophan biosynthesis. The isomerization is characterized by a monoexponential decay independent of phosphoribosyl anthranilate isomerase. Due to a tentative assignment of the fluorescent, primary product and the nonfluorescent, stable product to an enol and a keto compound, respectively, tryptophan biosynthesis appears to be rate-limited by an uncatalyzed enol/keto tautomerization. A formal kinetic mechanism of the reaction catalyzed by phosphoribosyl anthranilate isomerase is proposed that is consistent with the combined enzymic and ligand binding properties of the three variants of phosphoribosyl anthranilate isomerase.