SECOND TRANSPORT-SYSTEM FOR L-ARABINOSE IN ESCHERICHIA-COLI B/R CONTROLLED BY ARAC GENE
SECOND TRANSPORT-SYSTEM FOR L-ARABINOSE IN ESCHERICHIA-COLI B/R CONTROLLED BY ARAC GENE
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DOI：
10.1128/jb.111.2.606-613.1972
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发表时间：
1972-01-01
影响因子：
3.2
通讯作者：
HOGG, RW
中科院分区：
文献类型：
--
作者：
BROWN, CE;HOGG, RW
大肠杆菌B/r具有两个l-阿拉伯糖主动转运系统，这两个系统都受l-阿拉伯糖操纵子调控基因araC的调控。对l-阿拉伯糖具有较高亲和力的系统对l-阿拉伯糖的初始摄取的aKm为8.3 × 10− 6 m;较低亲和力的系统的aKm为1.0 × 10− 4 m。这两种系统也可以通过它们对作为初始摄取的竞争性抑制剂的类似物的反应的差异来区分。d-半乳糖强烈地抑制高亲和力系统对d-阿拉伯糖的摄取，但仅微弱地抑制低亲和力系统对d-岩藻糖、d-木糖、和β-甲基-L-阿拉伯糖苷竞争性地抑制两种系统对L-阿拉伯糖的摄取，抑制程度大致相同。来苏糖不抑制任一系统。基于动力学证据和缺乏这两个系统中的一个或另一个的突变体的性质，已经得出结论，高亲和力摄取系统涉及β-阿拉伯糖结合蛋白。动力学研究表明，高亲和力系统摄取l-阿拉伯糖的Km与结合蛋白结合l-阿拉伯糖的Km相似，并且两者对所测试的抑制底物具有相似的Ki值。对β-阿拉伯糖转运缺陷突变体的研究表明，先前描述的β-阿拉伯糖转运缺陷突变体缺乏低亲和力系统，但保留了高亲和力系统，并具有正常水平的β-阿拉伯糖结合蛋白。在本通信中描述的仅缺乏高亲和力系统的突变体或者不含可检测的1-阿拉伯糖结合蛋白，或者具有结合1-阿拉伯糖的能力降低的免疫交叉反应物质。这些观察结果支持了结合蛋白在l-阿拉伯糖摄取中的作用。
Escherichia coliB/r possesses two active transport systems forl-arabinose, both of which are regulated byaraC, the regulatory gene for thel-arabinose operon. The system with the higher affinity forl-arabinose has aKmfor initial uptake ofl-arabinose of 8.3 × 10−6m; the system of lower affinity has aKmof 1.0 × 10−4m. The two systems can also be distinguished by differences in their response to analogues that act as competitive inhibitors of initial uptake.d-Galactose strongly inhibitsl-arabinose uptake by the high affinity system but only weakly inhibits such uptake by the low affinity system.d-Fucose,d-xylose, and β-methyl-l-arabinoside competitively inhibit the uptake ofl-arabinose by both systems to approximately the same extent.d-Glucose andl-lyxose do not inhibit either system. On the basis of kinetic evidence and the properties of mutants lacking one or the other of the two systems, it has been concluded that the high affinity uptake system involves thel-arabinose binding protein. Kinetic studies have shown that theKmforl-arabinose uptake by the high affinity system resembles theKmfor binding ofl-arabinose by the binding protein, and both have similarKivalues for the inhibitory substrates tested. A consideration ofl-arabinose transport-deficient mutants has demonstrated that the previously describedaraEmutants lack the low affinity system but retain the high affinity system and have normal levels of thel-arabinose binding protein. Mutants described in this communication which lack only the high affinity system either contain no detectablel-arabinose binding protein or possess an immunologically cross-reacting material that is reduced in its ability to bindl-arabinose. These observations support a role for the binding protein inl-arabinose uptake.