Pachmann U, Zachau H G
Nucleic Acids Res. 1978 Mar;5(3):961-73. doi: 10.1093/nar/5.3.961.
Seryl tRNA synthetase from Saccharomyces Carlsbergensis C836 contains two sets of sites for tRNASer, L-serine, and Mg2+-ATP, both of which are involved in aminoacylation. This is based on the following experimental results: (a) at low serine concentrations, second order kinetics in tRNASer are observed; (b) biphasic kinetics result when the amino acid is the varied substrate indicating anticooperative binding of two serine molecules to the synthetase; (c) when two molecules of serine are bound the rate of aminoacylation increases strongly and becomes first order in tRNASer; (d) the involvement of more than one site for Mg2+ and ATP is deduced from systematic variations of the concentrations of Mg2+ and ATP. Implications of the anticooperative binding of the substrates for possible reaction mechanisms are discussed. The results indicate that under normal conditions, the activity of seryl tRNA synthetase is regulated mainly by tRNASer while at high serine concentrations regulation by the amino acid itself prevails.
卡尔斯伯酵母C836的丝氨酰tRNA合成酶含有两组用于tRNASer、L-丝氨酸和Mg2+-ATP的位点，二者均参与氨酰化反应。这是基于以下实验结果得出的：(a)在低丝氨酸浓度下，观察到tRNASer呈二级动力学；(b)当氨基酸作为可变底物时，会产生双相动力学，表明两个丝氨酸分子与合成酶的结合具有反协同性；(c)当两个丝氨酸分子结合时，氨酰化速率强烈增加并变为tRNASer的一级动力学；(d)从Mg2+和ATP浓度的系统变化推断出不止一个Mg2+和ATP位点的参与。讨论了底物反协同结合对可能反应机制的影响。结果表明，在正常条件下，丝氨酰tRNA合成酶的活性主要受tRNASer调节，而在高丝氨酸浓度下，氨基酸自身的调节起主导作用。
