Ruhrmann J, Krämer R
Institut für Biotechnologie I, Forschungszentrum Jülich, Germany.
J Bacteriol. 1992 Dec;174(23):7579-84. doi: 10.1128/jb.174.23.7579-7584.1992.
The energetics of the anaerobic gram-negative bacterium Zymomonas mobilis, a well-known ethanol-producing organism, is based solely on synthesis of 1 mol of ATP per mol of glucose by the Entner-Doudoroff pathway. When grown in the presence of glucose as a carbon and energy source, Z. mobilis had a cytosolic ATP content of 3.5 to 4 mM. Because of effective pH homeostasis, the components of the proton motive force strongly depended on the external pH. At pH 5.5, i.e., around the optimal pH for growth, the proton motive force was about -135 mV and was composed of a pH gradient of 0.6 pH units (internal pH 6.1) and a membrane potential of about -100 mV. Measurement of these parameters was complicated since ionophores and lipophilic probes were ineffective in this organism. So far, only glucose transport by facilitated diffusion is well characterized for Z. mobilis. We investigated a constitutive secondary glutamate uptake system. Glutamate can be used as a nitrogen source for Z. mobilis. Transport of glutamate at pH 5.5 shows a relatively high Vmax of 40 mumol.min-1.g (dry mass) of cells-1 and a low affinity (Km = 1.05 mM). Glutamate is taken up by a symport with two H+ ions, leading to substantial accumulation in the cytosol at low pH values.
运动发酵单胞菌是一种著名的产乙醇厌氧革兰氏阴性菌，其能量代谢仅基于通过恩特纳-杜德洛夫途径每摩尔葡萄糖合成1摩尔ATP。当在以葡萄糖作为碳源和能源的条件下生长时，运动发酵单胞菌的胞质ATP含量为3.5至4 mM。由于有效的pH稳态，质子动力的组成成分强烈依赖于外部pH。在pH 5.5时，即接近生长的最佳pH时，质子动力约为-135 mV，由0.6个pH单位的pH梯度（内部pH 6.1）和约-100 mV的膜电位组成。由于离子载体和亲脂性探针在这种生物体中无效，这些参数的测量很复杂。到目前为止，对于运动发酵单胞菌，只有通过易化扩散进行的葡萄糖转运得到了很好的表征。我们研究了一种组成型继发性谷氨酸摄取系统。谷氨酸可以用作运动发酵单胞菌的氮源。在pH 5.5时谷氨酸的转运显示出相对较高的Vmax，为40 μmol·min-1·g（干重）细胞-1，且亲和力较低（Km = 1.05 mM）。谷氨酸通过与两个H+离子的协同转运被摄取，导致在低pH值下在胞质溶胶中大量积累。
