Jacobs M H, van der Heide T, Driessen A J, Konings W N
Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
Proc Natl Acad Sci U S A. 1996 Nov 12;93(23):12786-90. doi: 10.1073/pnas.93.23.12786.
Growth of a glutamate transport-deficient mutant of Rhodobacter sphaeroides on glutamate as sole carbon and nitrogen source can be restored by the addition of millimolar amounts of Na+. Uptake of glutamate (Kt of 0.2 microM) by the mutant strictly requires Na+ (K(m) of 25 mM) and is inhibited by ionophores that collapse the proton motive force (pmf). The activity is osmotic-shock-sensitive and can be restored in spheroplasts by the addition of osmotic shock fluid. Transport of glutamate is also observed in membrane vesicles when Na+, a proton motive force, and purified glutamate binding protein are present. Both transport and binding is highly specific for glutamate. The Na(+)-dependent glutamate transporter of Rb. sphaeroides is an example of a secondary transport system that requires a periplasmic binding protein and may define a new family of bacterial transport proteins.
球形红细菌谷氨酸转运缺陷型突变体在以谷氨酸作为唯一碳源和氮源时的生长，可通过添加毫摩尔量的Na⁺得以恢复。该突变体对谷氨酸的摄取（Kt为0.2微摩尔）严格依赖Na⁺（K(m)为25毫摩尔），并受到能消除质子动力势（pmf）的离子载体的抑制。其活性对渗透压休克敏感，通过添加渗透压休克液可在原生质球中恢复。当存在Na⁺、质子动力势和纯化的谷氨酸结合蛋白时，在膜囊泡中也可观察到谷氨酸的转运。转运和结合对谷氨酸都具有高度特异性。球形红细菌的Na⁺依赖性谷氨酸转运体是一种次级转运系统的实例，该系统需要周质结合蛋白，可能定义了一个新的细菌转运蛋白家族。
