Active potassium extrusion regulated by intracellular pH in Streptococcus faecalis.
Potassium extrusion in bacteria is thought to play a role in the regulation of the cytoplasmic pH; in several organisms, it has been ascribed to secondary antiport of K+ for protons. Streptococcus faecalis exhibited a distinctive pattern: potassium extrusion occurred only when the cytoplasmic pH was alkaline and required the generation of ATP. The key observation is that glycolyzing cells suspended in an alkaline medium extruded K+, even against a K+ concentration gradient, provided the medium contained a weak permeant base (e.g. diethanolamine or methylamine). The amines render the cytoplasmic pH alkaline; when conditions were arranged to keep the cytoplasm neutral, no K+ extrusion was seen. Potassium extrusion required the presence of either glucose or arginine and was unaffected by protonophores and by inhibition of the F1Fo-ATPase. When the medium contained [14C]methylamine, the cells accumulated the base to an extent stoichiometrically equivalent to the K+ lost. Concurrently, the cytoplasmic pH fell from 8.8 to 7.6, at which point K+ extrusion ceased. The results suggest that K+ extrusion is due to an ATP-driven transport system that expels K+ by exchange for H+ and is active only at alkaline cytoplasmic pH.
Kakinuma
Y
Y
Faculty of Pharmaceutical Sciences, Inohana Campus, Chiba University, Japan.
Igarashi
K
K
D000255:Adenosine Triphosphate / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004734:Energy Metabolism; D013293:Enterococcus faecalis / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006096:Gramicidin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008962:Models, Theoretical; D011188:Potassium / Q000378:metabolism*; D027961:Potassium-Hydrogen Antiporters; D012458:Salicylanilides / Q000494:pharmacology
D002352:Carrier Proteins; D007461:Iodoacetates; D007476:Ionophores; D027961:Potassium-Hydrogen Antiporters; D012458:Salicylanilides; D006096:Gramicidin; D000255:Adenosine Triphosphate; C003390:3,3',4',5-tetrachlorosalicylanilide; D005947:Glucose; D011188:Potassium; D019807:Iodoacetic Acid