Kepes F
Biochimie. 1985 Jan;67(1):69-73. doi: 10.1016/s0300-9084(85)80231-5.
At the steady-state of accumulation of intracellular lactose by the beta-galactoside permease of Escherichia coli, the rate of efflux of the substrate is equal to its rate of influx. An original experimental method and a mathematical processing of the experimental data are proposed to evaluate the relative involvements of the permease-mediated pathway and of the diffusion component in this efflux. The method consists of inducing the lac operon of the bacteria, and then of removing the inducer and allowing the cells to grow further. The permease content and the membrane surface of diffusion are thus varying independently in such a "de-induction" experiment, along which lactose uptake has been monitored at different times. The analysis of the experimental data show that, under conditions of maximal induction, over 95% of the efflux passes through the energized permease. The relevant parameters of the efflux of lactose have been computed and their values allow the prediction of most classical observations, as well as the prediction, never checked, that under physiological conditions, the higher the external substrate concentration, the higher the permease-mediated efflux, according to a saturation kinetics.
在大肠杆菌的β-半乳糖苷通透酶使细胞内乳糖积累达到稳态时，底物的流出速率等于其流入速率。本文提出了一种原始的实验方法以及对实验数据的数学处理方法，以评估通透酶介导的途径和扩散成分在这种流出过程中的相对参与程度。该方法包括诱导细菌的乳糖操纵子，然后去除诱导剂并让细胞进一步生长。在这样的“去诱导”实验中，通透酶含量和扩散的膜表面积因此独立变化，在此过程中不同时间监测了乳糖摄取情况。实验数据分析表明，在最大诱导条件下，超过95%的流出通过有能量供应的通透酶。已计算出乳糖流出的相关参数，其值能够预测大多数经典观察结果，以及预测（从未验证过）在生理条件下，根据饱和动力学，外部底物浓度越高，通透酶介导的流出越高。
