ABSTRACT
The retention of high potassium levels in Escherichia coli is not dependent on intact energy metabolism, since without the presence of a carbon source or in the presence of energy inhibitors significant K+ gradients can be maintained. In contrast, with 0.5 mM N-ethylmaleimide, K+ depletion is immediate and complete. As a final result, intracellular K+ is approximately three times more concentrated than the K+ in the medium. Increase of K+ in the medium is immediately followed by K+ uptake whereas in the unpoisoned state only an increase in the osmotic pressure of the medium would result in an increase of the K+ pool. The intracellular K+ undergoes continuous turnover in the poisoned cells whereas in intact cells turnover is strictly dependent on the presence of a metabolizable carbon source. After removal of the thiol reagent the cell recovers its capacity to concentrate potassium. The recovery process is inhibited by energy inhibitors or by incubation at low temperature but not by chloramphenicol. It is only slightly slowed down by carbon or sulfur starvation. The leak provoked by N-ethylmaleimide is similar in wild-type E. coli cells when a derepressed kdp uptake system working in the micromolar range of the K+ concentration is responsible for the intracellular pool of K+ and when, in a medium millimolar K+ concentration range, the trkA and trkD systems are predominant.