title: Active transport of thallous ions by Streptococcus lactis.
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.
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D013291:Streptococcus / Q000378:metabolism*; D013793:Thallium / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; D012965:Sodium Chloride; D013793:Thallium; D011188:Potassium