Jacobs M H, Driessen A J, Konings W N
Department of Microbiology, University of Groningen, Haren, The Netherlands.
J Bacteriol. 1995 Apr;177(7):1812-6. doi: 10.1128/jb.177.7.1812-1816.1995.
The mechanism of L-glutamate uptake was studied in Rhodobacter sphaeroides. Uptake of L-glutamate is mediated by a high-affinity (Kt of 1.2 microM), shock-sensitive transport system that is inhibited by vanadate and dependent on the internal pH. From the shock fluid, an L-glutamate-binding protein was isolated and purified. The protein binds L-glutamate (apparent Kd of 1.3 microM) and L-glutamine (Ki of 15 microM) with high affinity. The expression level of this binding protein is maximal at limiting concentrations of glutamine in the growth medium. The glutamate-binding protein restores the uptake of L-glutamate in spheroplasts. L-Aspartate is a strong competitive inhibitor of L-glutamate uptake (Ki of 3 microM) but competes only poorly with L-glutamate for binding to the binding protein (Ki of > 200 microM). The uptake of L-aspartate in R. sphaeroides also involves a binding protein which is distinct from the L-glutamate-binding protein. These data suggest that in R. sphaeroides, the L-glutamate- and L-aspartate-binding proteins interact with the same membrane transporter.
在球形红细菌中研究了L-谷氨酸的摄取机制。L-谷氨酸的摄取由一种高亲和力（Kt为1.2微摩尔）、对休克敏感的转运系统介导，该系统受钒酸盐抑制且依赖于内部pH值。从休克液中分离并纯化出一种L-谷氨酸结合蛋白。该蛋白以高亲和力结合L-谷氨酸（表观Kd为1.3微摩尔）和L-谷氨酰胺（Ki为15微摩尔）。在生长培养基中谷氨酰胺浓度有限时，这种结合蛋白的表达水平最高。谷氨酸结合蛋白可恢复原生质球对L-谷氨酸的摄取。L-天冬氨酸是L-谷氨酸摄取的强竞争性抑制剂（Ki为3微摩尔），但与L-谷氨酸竞争结合结合蛋白的能力较差（Ki大于200微摩尔）。球形红细菌中L-天冬氨酸的摄取也涉及一种与L-谷氨酸结合蛋白不同的结合蛋白。这些数据表明，在球形红细菌中，L-谷氨酸结合蛋白和L-天冬氨酸结合蛋白与同一膜转运体相互作用。
