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

At a concentration of 10 −6 m , 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 14 C-uracil into ribonucleic acid but incorporation of 14 C-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.