NA-CHLOROPHENYLURETHANE-MONENSIN IN ENTEROCOCCUS-HIRAE DEENERGIZED AND ENERGIZED CELLS STUDIED BY NA-23-NMR AND K+ ATOMIC-ABSORPTION( AND K+ TRANSPORT BY 4)

Na+ and K+ movements induced by 4-chlorophenylurethane-monensin, which presents an inverted ion selectivity (K+>Na+) in model systems compar ed with monensin, were followed on Enterococcus hirae cells by Na-23-N MR and K+ atomic absorption. For de-energized cells, the urethane deri vative is much more selective for K+ than monensin, but only at low co ncentrations (10(-3)-10(-4) mM). For higher concentrations, as previou sly shown for monensin, the sodium and potassium movements are driven by the ion gradients present. On energized cells, both K+ and Na+ grad ients were highly perturbed, and this can be related to the higher tox icity in mice and bacteria for this derivative.