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J Bacteriol. 1968 March; 95(3): 816-823
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

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

Division of Research, National Jewish Hospital, Denver, Colorado 80206
² Department of Microbiology, University of Colorado, School of Medicine, Denver, Colorado 80220

ABSTRACT

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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