Nichols W W, Young S N
Biochem J. 1985 Jun 1;228(2):505-12. doi: 10.1042/bj2280505.
The transport of [3H]dihydrostreptomycin into the cytoplasm of Escherichia coli was distinguished, by its respiration-dependent nature, from binding within the cell envelope. 1. Of the radiolabel in the cytoplasm, 70-90% was dissolved in, or quickly equilibrated with, the cytoplasmic aqueous phase because this proportion rapidly left cells treated with toluene or with butan-1-ol. 2. After a period of respiration-dependent uptake of [3H]dihydrostreptomycin, cells were washed repeatedly by centrifugation and resuspension. Radiolabel did not leave the cells at any appreciable rate. 3. Uptake of dihydrostreptomycin (at an exogenous concentration of 1 mg of base/ml) was monitored for 2h to an apparent equilibrium. Then the specific radioactivity of exogenous dihydrostreptomycin was raised without significantly altering its chemical concentration. There was no exchange of radiolabel between the exogenous pool and the cytoplasmic pool. 4. Dihydrostreptomycin was not taken up by respiring, cytoplasm-free membrane vesicles which accumulated L-proline in control experiments. These data support the view that respiration-dependent uptake of dihydrostreptomycin by E. coli is not simply a secondary translocation process such as uniport.
[3H]双氢链霉素向大肠杆菌细胞质的转运，因其对呼吸的依赖性，与在细胞包膜内的结合有所不同。1. 细胞质中的放射性标记物，70 - 90%溶解于细胞质水相或与之快速达到平衡，因为这一比例的放射性标记物会迅速从经甲苯或丁醇处理的细胞中逸出。2. 在经历一段对呼吸有依赖性的[3H]双氢链霉素摄取过程后，通过离心和重悬对细胞进行反复洗涤。放射性标记物不会以任何可观的速率从细胞中逸出。3. 监测双氢链霉素（外源浓度为1 mg碱基/ml）的摄取2小时直至明显达到平衡。然后提高外源双氢链霉素的比放射性，而不显著改变其化学浓度。外源库与细胞质库之间没有放射性标记物的交换。4. 在对照实验中积累L - 脯氨酸的有呼吸作用但无细胞质的膜囊泡不会摄取双氢链霉素。这些数据支持这样一种观点，即大肠杆菌对双氢链霉素的呼吸依赖性摄取并非简单的二级转运过程，如单向转运。
