Abstract
Tl+ ions have been shown to mimic or compete with K+ in a number of membrane systems. We confirmed that in starved, valinomycin-treated cells of Streptococcus lactis 7962, Tl+ ions distributed themselves across the bacterial membrane in response to the potassium diffusion potential. In glucose-energized cells, however, Tl+ was taken up by a system specifically stimulated by sodium salts. The intracellular levels of Tl+ exceeded those attained by [3H]triphenylmethylphosphonium ion, a lipophilic cation which accumulates in response to the membrane potential. The uptake of Tl+ by (Na+ and glucose)-stimulated cells was strongly inhibited by potassium salts. These experiments suggest that metabolic energy is coupled to Tl+ transport by means of a high energy phosphate compound and that Tl+ ions are actively transported by a membrane carrier whose normal substrate is K+. The uptake of Tl+ is not a valid method for determining the streptococcal membrane potential.
Highlights
Active Transport of Thallous Ions by Streptococcus lactis*We confirmed that in starved, valinomycin-treated cells of Streptococcus Zuctis 7962, Tl’ ions distributed themselves across the bacterial membrane in response to the potassium diffusion potential
K+ in a number of membrane systems
In glucose-energized cells, Tl+ was taken up by a system stimulated by sodium salts
Summary
We confirmed that in starved, valinomycin-treated cells of Streptococcus Zuctis 7962, Tl’ ions distributed themselves across the bacterial membrane in response to the potassium diffusion potential. Glucose)-stimulated cells was strongly inhibited by potassium salts. These experiments suggest that metabolic energy is coupled to Tl’ transport by means of a high energy phosphate compound and that Tl’ ions are actively transported by a membrane carrier whose normal substrate is K+. The cells were harvested, washed, and resuspended to about 3 mg dry weight/ml in the buffer to be used in the uptake experiments (see below). Each milliliter of reaction mixture contained about 0.3 mg dry weight of cells and 0.5 to 1 x 10” cpm of radioactivity.
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