Mode of action of colicin Ia: effect of colicin on the Escherichia coli proton electrochemical gradient.

By use of the technique of flow dialysis, the membrane potential (deltapsi) and pH gradient (deltapH) have been measured in colicin Ia-treated Escherichia coli K-12 cells and in membrane vesicles prepared from such cells. Although such cells and vesicles are able to generate a transmembrane deltapH at pH 5.5, they do not generate a transmembrane deltapsi. Glucose-6-phospate uptake by cells is shown to be stimulated at pH 5.5 and inhibited at pH 7.5 by colicin Ia treatment. On the other hand, proline uptake is demonstrated to be inhibited progressively at pH 5.5, 6.6, and 7.5 in colicin Ia-treated cells. These data provide strong evidence for a colicin Ia-induced membrane deplorization and indicate that the membrane becomes permeable to ion(s) other than protons after treatment with colicin Ia.