COMPARISON OF THE ENZYMATIC-PROPERTIES OF THE 2 ESCHERICHIA-COLI LYSYL-TRANSFER-RNA SYNTHETASE SPECIES
COMPARISON OF THE ENZYMATIC-PROPERTIES OF THE 2 ESCHERICHIA-COLI LYSYL-TRANSFER-RNA SYNTHETASE SPECIES
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DOI：
10.1074/jbc.270.24.14439
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发表时间：
1995-06-16
影响因子：
4.8
通讯作者：
PLATEAU, P
中科院分区：
文献类型：
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作者：
BREVET, A;CHEN, J;PLATEAU, P
在大肠杆菌中，赖氨酰-tRNA 合成酶活性由组成型 lysS 基因或诱导型 lysU 编码。这两种相应的酶可以分别从 Delta lysU 和 Delta lysS 菌株中同质纯化。纯酶 LysS 和 LysU 的比较表明，在饱和底物存在的情况下，LysS 的活性大约是 lysS 的两倍。 LysU 参与 ATP-PPi 交换以及 tRNA(Lys) 氨酰化反应。此外，LysU-赖氨酸复合物的解离常数比LysS-赖氨酸复合物小8倍。与此差异一致，LysU的活性对尸胺的添加比LysS的活性更不敏感，尸胺是赖氨酸的脱羧产物，是赖氨酸与其合成酶结合的竞争性抑制剂。这一观察表明，在引起尸胺的生理条件下，LysU可能具有有用的作用。在细菌中积累。值得注意的是，这些条件也诱导 lysU 表达。在 Ap,A 合成中还比较了均质 LysU 和 LysS。 LysU 在产生这种二核苷酸时的活性仅比 LysS 高 8 倍，这使得热诱导型 LysU 物种不太可能优先参与应激大肠杆菌细胞内 Ap(4)A 的积累。通过确定 Delta lysU 以及 lysU(+) 菌株中 Ap(4)A 浓度（N = A、C、G 或 U）在48 摄氏度下 1 小时的温度变化。两种菌株的测量浓度值相同。
In Escherichia coli, lysyl-tRNA synthetase activity is encoded by either a constitutive lysS gene or an inducible one, lysU, The two corresponding enzymes could be purified at homogeneity from a Delta lysU and a Delta lysS strain, respectively, Comparison of the pure enzymes, LysS and LysU, indicates that, in the presence of saturating substrates, LysS is about twice more active than LysU in the ATP-PPi exchange as well as in the tRNA(Lys) aminoacylation reaction. Moreover, the dissociation constant of the LysU-lysine complex is 8-fold smaller than that of the LysS-lysine complex, In agreement with this difference, the activity of LysU is less sensitive than that of LysS to the addition of cadaverine, a decarboxylation product of lysine and a competitive inhibitor of lysine binding to its synthetase, This observation points tla a possible useful role of LysU, under physiological conditions causing cadaverine accumulation in the bacterium. Remarkably, these conditions also induce lysU expression.Homogeneous LysU and LysS were also compared in Ap,A synthesis. LysU is only 8-fold more active than LysS in the production of this dinucleotide, This makes unlikely that the heat-inducible LysU species could be preferentially involved in the accumulation of Ap(4)A inside stressed Escherichia coli cells, This conclusion could be strengthened by determining the concentrations of Ap(4)N (N = A, C, G, or U) in a Delta lysU as well as in a lysU(+) strain, before and after a 1-h temperature shift at 48 degrees C. The measured concentration values were the same in both strains.