SODIUM-DEPENDENT GLUTAMATE TRANSPORT IN MEMBRANE-VESICLES OF ESCHERICHIA-COLI K-12
SODIUM-DEPENDENT GLUTAMATE TRANSPORT IN MEMBRANE-VESICLES OF ESCHERICHIA-COLI K-12
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DOI：
10.1016/0014-5793(75)81099-4
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发表时间：
1975-01-01
期刊：
影响因子：
3.5
通讯作者：
KABACK, HR
中科院分区：
文献类型：
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作者：
KAHANE, S;MARCUS, M;KABACK, HR
突变体E.利用谷氨酸作为主要碳源的大肠杆菌K12比不能在该氨基酸上生长的野生型菌株更有效地转运谷氨酸[1 -4]。在一种这样的突变体（菌株CS 7）中的谷氨酸转运已被证明需要钠，这增加了转运系统对谷氨酸的表观亲和力，但不影响其能力[5]。也有报道E.大肠杆菌K-12表现出载体介导的谷氨酸一级外排;然而，外排速率不因增加谷氨酸摄取速率的突变而改变[6- 81]。最近，已从菌株CS 7中分离出特异性谷氨酸结合蛋白，并纯化至均一性[9，10]。的K，L谷氨酸结合到这种蛋白质和Ki值的某些谷氨酸类似物是类似的适当的动力学值在完整的细胞中获得的谷氨酸转运。此外，具有增加的谷氨酸转运活性的突变体具有几乎两倍于野生型亲本的谷氨酸结合蛋白[9，10]。虽然这些发现暗示了谷氨酸结合蛋白在转运中的作用，但从利用谷氨酸的突变体制备的膜囊泡转运谷氨酸比野生型制剂好10倍以上，但没有可检测到的结合蛋白[1]。本研究表明，谷氨酸转运在膜囊泡的菌株CS 7也需要钠，而没有这样的要求是显而易见的谷氨酸结合纯化的结合蛋白。
Mutants of E. coli Kl 2 which utilize glutamate as a major carbon source transport glutamate more effectively than wild type strains which are unable to grow on this amino acid [l-4]. Glutamate transport in one such mutant, strain CS7, has been shown to require sodium which increases the apparent affinity of the transport system for glutamate, but does not affect its capacity [5]. It has also been reported that E. coli K-12 exhibits carrier-mediated, first-order efflux of glutamate; however, the efflux rate is not altered by mutations which increase the rate of glutamate uptake [6-81.Recently, a specific glutamate-binding protein has been isolated from strain CS7, and purified to homogeneity [9, 10]. The K, for Lglutamate binding to this protein and the Ki values for certain glutamate analogues are similar to the appropriate kinetic values obtained for glutamate transport in intact cells. Moreover, mutants with increased glutamate transport activity have almost twice as much glutamate-binding protein as the wild-type parent [9, 10]. Although these findings implicate the glutamate-binding protein in transport, membrane vesicles prepared from glutamateutilizing mutants transport glutamate more than 1 O-times better than wild-type preparations, but have no detectable binding protein [1 l]. The present study demonstrates that glutamate transport in membrane vesicles of strain CS7 also requires sodium, while no such requirement is apparent for glutamate binding to purified binding protein.