Absence of a unique relationship between proton-motive force and active lactose transport in E. coli

In our study we progressively decreased the proton-motive force of whole E. coli cells, by the addition of increasing amounts of protonophores (which permeabilize the membrane to protons) or inhibitors of the electron flow in electron transfer chains. In each case, the proton-motive force and speed of lactose transport or its accumulation in the stationary state are measured. We worked under external pH conditions such that the proton-motive force is reduced to its electrical component. This was done in order to simplify the proton-motive force measurement and improve accuracy. The results we obtained show unambiguously that there are no unique relationships between proton-motive force and active transport