The effects of weak acids on potassium uptake by Escherichia coli K-12 inhibition by low cytoplasmic pH.

The activity of the Escherichia coli K+ transport system TrkA was measured as a function of the cytoplasmic pH of the cell. For this purpose, pHin was decreased by the addition of the weak acids acetic acid, benzoic acid or salicylic acid to K+-depleted cells. Under these conditions, the initial rate of K+ uptake decreased strongly with pHin, and was almost independent of the acid used. This inhibition was due to a strong decrease in the Vmax for K+ uptake, which indicates that low cytoplasmic pH inactivates the TrkA K+ uptake system. The relevance of this inhibition for growth and metabolism at low pHin is discussed.