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Gramicidin, Valinomycin, and Cation Permeability of Streptococcus faecalis

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

ABSTRACT

Gramicidin and valinomycin in concentrations of 10^–7 and 10^–6M, respectively, inhibited the growth of Streptococcus faecalis. Inhibition of growth was associated with loss of Rb⁺ and K⁺ from the cells, and could be reversed by addition of excess K⁺. Cells treated with these antibiotics exhibited greatly increased permeability to certain cations; no effect was observed on the penetration of other small molecules. Unlike normal cells, cells treated with gramicidin rapidly lost internal Rb⁺ by passive exchange with external cations, including H⁺, all monovalent alkali metals, NH₄⁺, Mg⁺⁺, and tris(hydroxymethyl)aminomethane. Exchange was rapid even at 0 C and was independent of energy metabolism. The effect of valinomycin was more selective. Cellular Rb⁺ was rapidly displaced by external H⁺, K⁺, Rb⁺, and Cs⁺; other cations were less effective. The exchange was independent of metabolism but strongly affected by temperature. Under certain conditions, polyvalent cations inhibited exchange between ⁸⁶Rb and Rb⁺ induced by valinomycin. The antibiotic apparently neither stimulates nor inhibits the energy-dependent K⁺ pump of S. faecalis, but exerts its effect on the passive permeability of the membrane to cations. The increased permeability to specific cations induced by gramicidin and valinomycin is a sufficient explanation for the inhibition of growth, glycolysis, and other processes.

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