Isoleucyl transfer ribonucleic acid synthetase. The role of magnesium in amino acid activation.
Isoleucyl transfer ribonucleic acid synthetase. The role of magnesium in amino acid activation.
复制标题
异亮氨酰转移核糖核酸合成酶。
DOI：
10.1021/bi00818a005
复制
发表时间：
1970
期刊：
影响因子：
2.9
通讯作者：
P. Schimmel
中科院分区：
文献类型：
--
作者：
F. Cole;P. Schimmel
框架X。Colef和Paul R.研究了镁对tRNA合成酶氨基酸活化反应速率的影响。反应如文中所示。在pH 8，0，0.4 m Na+，25，用来自大肠杆菌B的异亮氨酰tRNA合成酶测量方程式1a的平衡速度V。研究了V在ATP，焦磷酸盐和镁浓度的排列变化，使用standardATP-[8 2 P]焦磷酸盐同位素交换反应。发现镁可充当式Ia的活化剂和抑制剂两者。在不存在镁的情况下，未检测到反应。在给定的ATP和焦磷酸盐水平下，增加镁的浓度会增加氨基酸活化的速率，直到达到最大速率。此时，速率对镁水平的进一步小幅增加不敏感，但高浓度（10 mM）会导致速率下降。此外，底物ATP和焦磷酸盐能激活或抑制反应，部分取决于镁的浓度，然后将测得的速率与实验条件下存在的各种离子形式的ATP和焦磷酸盐的浓度相关联。开发了用于计算各种ATP和焦磷酸盐物质的浓度的方程，作为以下的函数：
Frames X. Colef and Paul R. Schimmel abstract: The effect of magnesium on the rate of the amino acid activation reaction oftRNA synthetases has been investi-gated. Thereaction is eq la of the text. Measurements of the equilibrium velocity, V, of eq la were conducted with isoleucyl tRNA synthetase from Escherichia coli B, at pH 8, 0, 0.4 m Na+, 25. V was investigated over a permutational variation of ATP, pyrophosphate, and magnesium concentrations, using the standardATP-[8 2P] pyrophosphate isotope-exchange reaction. It was found that magnesium can serve as both an activator and an inhibitor of eq la. There is no detectable re-action in the absence of magnesium. At a given level of ATP and pyrophosphate, increasing concentrations of magnesium give increased rates of amino acid activation until a maximal rate is achieved. At this point the rate is insensitive to further small increases in the level of magnesium, but high concen-trations (10 mM) cause a drop in rate. Furthermore, thesubstrates ATP and pyrophosphate can activate or inhibit the reaction depending, in part, on the concentration of magnesium.The measured rates are then correlated with the con-centrations of the variousionic forms of ATP and pyrophos-phate which exist under the conditions of the experiments. Equations are developed for calculating the concentrations of the various ATP and pyrophosphate species as a function of