Effects of Nigericin and Monactin on Cation Permeability of Streptococcus faecalis and Metabolic Capacities of Potassium-depleted Cells

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RESUMO

At a concentration of 10−6m, nigericin and monactin inhibited growth of Streptococcus faecalis, and the inhibition was reversed by addition of excess K+. In the presence of certain antibiotics, the cells exhibited increased permeability to certain cations; internal Rb+ was rapidly lost by exchange with external H+, K+ Rb+, and, more slowly, with Na+ and Li+. No effect was observed on the penetration of other small molecules. Cation exchanges induced by nigericin and monactin were metabolically passive and apparently did not involve the energy-dependent K+ pump. When the cells were washed, the cytoplasmic membrane recovered its original impermeability to cations. By use of monactin, we prepared cells whose K+ content had been completely replaced by other cations, and the metabolic characteristics of K+-depleted cells were studied. Cells containing only Na+ glycolyzed almost as well as did normal ones and, under proper conditions, could accumulate amino acids and orthophosphate. These cells also incorporated 14C-uracil into ribonucleic acid but incorporation of 14C-leucine into protein was strictly dependent upon the addition of K+. When K+ or Rb+ was added to sodium-loaded cells undergoing glycolysis, these ions were accumulated by stoichiometric exchange for Na+. From concurrent measurements of the rate of glycolysis, it was calculated that one mole-pair of cations was exchanged for each mole of adenosine triphosphate produced.

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