The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli

Jean-Claude Patte, Paolo Truffa-Bachi, Georges N. Cohen
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引用次数: 91

Abstract

In Escherichia coli K12,

  • 1.

    1. A single mutation can lead to the concomitant modification or to the concomitant loss of the two activities, threonine-sensitive β-aspartokinase (ATP: L-aspartate 4-phosphotransferase, EC 2.7.2.4) and threonine-sensitive homoserine dehydrogenase (L-homoserine: NADP+ oxidoreductase, EC 1.1.1.3).

  • 2.

    2. The two activities cannot be separated and the ratio of the specific activities remains constant throughout a 600-fold purification.

  • 3.

    3. The substrates of one of the activities are inhibitors of the otther activity. The observed inhibitions are specific.

  • 4.

    4. The threonine-sensitive aspartokinase is protected against thermal inactivation by NADPH, a substrate of the homoserine dehydrogenase.

  • 5.

    5. The conclusion is drawn that the two activities under study are carried by a single protein molecule. The apparent molecular mass of this complex protein is changed in some mutants. There is no apparent correlation between the apparent molecular mass and the cooperativity of inhibitor molecules.

  • 6.

    6. The significance of these findings is discussed in terms of metabolic regulation and intracellular topology.

大肠杆菌对苏氨酸敏感的同型丝氨酸脱氢酶和天冬氨酸激酶活性
在大肠杆菌K12中,1.1。单个突变可导致苏氨酸敏感的β-天冬氨酸激酶(ATP: l -天冬氨酸4-磷酸转移酶,EC 2.7.2.4)和苏氨酸敏感的同型丝氨酸脱氢酶(l -同型丝氨酸:NADP+氧化还原酶,EC 1.1.1.3)的同时修饰或同时丧失。这两种活性不能分离,特定活性的比例在600倍的净化过程中保持不变。其中一种活性的底物是另一种活性的抑制剂。观察到的抑制是特定的。对苏氨酸敏感的天冬氨酸激酶可通过NADPH(同型丝氨酸脱氢酶的底物)防止热失活。结果表明,所研究的两种活性是由一个蛋白质分子携带的。这种复杂蛋白的表观分子质量在某些突变体中发生了变化。表观分子质量与抑制剂分子的协同性之间没有明显的相关性。这些发现的意义在代谢调节和细胞内拓扑方面进行了讨论。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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