Speth A R, Hund H K, Lingens F
Institut für Mikrobiologie, Universität Hohenheim, Stuttgart.
Biol Chem Hoppe Seyler. 1989 Jun;370(6):591-9. doi: 10.1515/bchm3.1989.370.1.591.
The enzymes of the terminal steps of the phenylalanine and tyrosine biosynthesis were partially purified and characterized in Microtetraspora glauca, a spore-forming member of the order Actinomycetales. This bacterium relies exclusively on the phenylpyruvate route for phenylalanine synthesis, no arogenate dehydratase activity being found. Prephenate dehydratase is subject to feedback inhibition by phenylalanine, tyrosine and tryptophan, each acting as competitive inhibitor by increasing the Km of 72 microM for prephenate. Based on the results of gel chromatography on Sephadex G-200, the molecular mass of about 110,000 Da is not altered by any of the effectors. The enzyme is quite sensitive to inhibition by 4-hydroxymercuribenzoate. Microtetraspora glauca can utilize arogenate and 4-hydroxyphenylpyruvate as intermediates in tyrosine biosynthesis. Prephenate and arogenate dehydrogenase activities copurifying from ion exchange columns with coincident profiles were detected. From gel-filtration columns the two activities eluted at an identical molecular-mass position of about 68,000 Da. The existence of a single protein exhibiting substrate ambiguity is consistent with the findings, that both dehydrogenases have similar chromatographic properties, exhibit cofactor requirement for NAD and are inhibited to the same extent by tyrosine and 4-hydroxymercuribenzoate.
在放线菌目产孢成员蓝灰小多孢菌中，苯丙氨酸和酪氨酸生物合成终末步骤的酶被部分纯化并进行了特性分析。该细菌完全依赖苯丙酮酸途径合成苯丙氨酸，未发现预苯酸脱水酶活性。预苯酸脱水酶受到苯丙氨酸、酪氨酸和色氨酸的反馈抑制，每种氨基酸均通过增加对预苯酸72微摩尔的米氏常数而作为竞争性抑制剂起作用。基于在葡聚糖凝胶G - 200上的凝胶色谱结果，约110,000道尔顿的分子量不受任何效应物影响。该酶对4 - 羟基汞苯甲酸的抑制相当敏感。蓝灰小多孢菌可利用预苯酸和4 - 羟基苯丙酮酸作为酪氨酸生物合成的中间产物。检测到从离子交换柱共纯化的预苯酸和预苯酸脱氢酶活性具有一致的图谱。从凝胶过滤柱上，这两种活性在约68,000道尔顿的相同分子量位置洗脱。存在一种表现出底物模糊性的单一蛋白质与以下发现一致，即两种脱氢酶具有相似的色谱特性，对NAD有辅因子需求，并且受到酪氨酸和4 - 羟基汞苯甲酸的抑制程度相同。
