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首页> 外文期刊>Biochemistry >Escherichia coli glutamine synthetase adenylyltransferase (ATase, EC 2.7.7.49): kinetic characterization of regulation by PII, PII-UMP, glutamine, and alpha-ketoglutarate.
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Escherichia coli glutamine synthetase adenylyltransferase (ATase, EC 2.7.7.49): kinetic characterization of regulation by PII, PII-UMP, glutamine, and alpha-ketoglutarate.

机译：大肠杆菌谷氨酰胺合成酶腺苷酸转移酶（ATase，EC 2.7.7.49）：由PII，PII-UMP，谷氨酰胺和α-酮戊二酸调节的动力学特征。

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摘要

Glutamine synthetase adenylyltranferase (ATase, EC 2.7.7.49) catalyzes the adenylylation and deadenylylation of glutamine synthetase (GS), regulating GS activity. The adenylyltransferase (AT) reaction is activated by glutamine and by the unmodified form of the PII signal transduction protein and is inhibited by the uridylylated form of PII, PII-UMP. Conversely, the adenylyl-removing (AR) reaction is activated by PII-UMP and is inhibited by glutamine and by PII. Both AT and AR reactions are regulated by alpha-ketoglutarate, which binds to PII and PII-UMP. Here, we present a kinetic analysis of the AT and AR activities and their regulation. Both AT and AR reactions used a sequential mechanism of rapid equilibrium random binding of substrates and products. Activators and inhibitors had little effect on the binding of substrates, instead exerting their effects on catalysis. Our results were consistent with PII, PII-UMP, and glutamine shifting the enzyme among at least six different enzyme forms, two of which were inactive, one of which exhibited AR activity, and three of which exhibited AT activity. In addition to a site for glutamine, the enzyme appeared to contain two distinct sites for PII and PII-UMP. The PII, PII-UMP, and glutamine sites were in communication so that the apparent activation and inhibition constants for regulators depended upon each other. The binding of PII was favored by glutamine and its level reduced by PII-UMP, whereas glutamine and PII-UMP competed for the enzyme. alpha-Ketoglutarate, which acts exclusively through its binding to PII and PII-UMP, did not alter the binding of PII or PII-UMP to the enzyme. Rather, alpha-ketoglutarate dramatically affected the extent of activation or inhibition of the enzyme by PII or PII-UMP. A working hypothesis for the regulation of the AT and AR activities, consistent with all data, is presented.
机译：谷氨酰胺合成酶腺苷酸转移酶（ATase，EC 2.7.7.49）催化谷氨酰胺合成酶（GS）的腺苷酸化和腺苷酸化，调节GS的活性。谷氨酰胺和未修饰形式的PII信号转导蛋白可激活腺苷酸转移酶（AT）反应，并被PII-PII-UMP的尿嘧啶化形式抑制。相反，脱腺苷基（AR）反应被PII-UMP激活，并被谷氨酰胺和PII抑制。 AT和AR反应均受与PII和PII-UMP结合的α-酮戊二酸调节。在这里，我们介绍了AT和AR活动及其调节的动力学分析。 AT反应和AR反应都使用了快速平衡底物和产物的随机结合的顺序机制。活化剂和抑制剂对底物的结合几乎没有影响，反而对催化起作用。我们的结果与PII，PII-UMP和谷氨酰胺在至少六种不同酶形式之间转移该酶是一致的，其中两种是无活性的，一种表现出AR活性，而三种表现出AT活性。除谷氨酰胺位点外，该酶似乎还包含两个不同的PII和PII-UMP位点。 PII，PII-UMP和谷氨酰胺位点是连通的，因此调节剂的表观活化和抑制常数彼此依赖。谷氨酰胺促进了PII的结合，而PII-UMP降低了其水平，而谷氨酰胺和PII-UMP竞争该酶。仅通过与PII和PII-UMP结合而起作用的α-酮戊二酸不会改变PII或PII-UMP与酶的结合。相反，α-酮戊二酸酯极大地影响了PII或PII-UMP对酶的激活或抑制程度。提出了与所有数据一致的AT和AR活动调节的可行假设。

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