Aspartate transcarbamylase from Escherichia coli I. Inhibition by inorganic anions

Kjell Kleppe
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引用次数: 29

Abstract

  • 1.

    1. The effect of different inorganic anions on the catalytic activity of native and subunit aspartate transcarbamylase (carbamoylphosphate: l-aspartate carbamoltransferase, EC 2.1.3.2) has been investigated at pH 7.0 and 25°.

  • 2.

    2. Several inorganic anions were found to inhibit both native and subunit aspartate transcarbamylase. The order of effectiveness for the best inhibitors was: PPi > F > Pi > SO42−.

  • 3.

    3. For each ion except F, a strict competitive relationship was observed between the anion inhibitors and the substrate carbamyl phosphate.

  • 4.

    4. The concentration of l-aspartate also greatly influenced the magnitude of the inhibition. The inhibition increased with increasing concentration of l-aspartate.

  • 5.

    5. The effect of F was shown to be due to a displacement of the pH curve along the pH axis. F inhibited native asparatate transcarbamylase below pH 8 and activated it above this pH.

  • 6.

    6. Possible mechanisms of inhibition are discussed, and it is suggested that an inhibitor-l-aspartate complex is formed at the active site.

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大肠杆菌的天冬氨酸转氨基酶1 .无机阴离子的抑制作用
1.1. 研究了不同无机阴离子在pH 7.0和25°0.2.2条件下对天然和亚单位天冬氨酸氨基转移酶(氨基酰基磷酸酯:l-天冬氨酸氨基转移酶,EC 2.1.3.2)催化活性的影响。一些无机阴离子被发现抑制天然和亚基天冬氨酸转氨基酶。最佳抑制剂的有效性顺序为:PPi >F−祝辞π的在SO42−.3.3。除F−外,阴离子抑制剂与底物氨甲酰磷酸盐之间存在严格的竞争关系。l-天冬氨酸的浓度对抑制的程度也有很大影响。随着l-天冬氨酸浓度的增加,抑制作用增强。F−的影响是由于pH曲线沿pH轴的位移引起的。F−在pH低于8时抑制天然天冬氨酸转甲氨基酰基酶,在pH高于6.6时激活它。讨论了可能的抑制机制,认为在活性位点形成了抑制剂-l-天冬氨酸复合物。
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