title: Potassium transport coupled to ATP hydrolysis in reconstituted proteoliposomes of yeast plasma membrane ATPase.
abstract: Potassium transport coupled to ATP hydrolysis has been reconstituted in proteoliposomes using a highly purified plasma membrane Mg2+-dependent ATPase of the yeast Schizosaccharomyces pombe. The ATPase activity in the incorporated enzyme was strongly stimulated (2.2-fold) by the H+-conducting agent carbonyl cyanide m-chlorophenylhydrazone (CCCP). The H+/K+ exchanger nigericin (in the presence of K+) stimulated 1.6-fold the ATPase activity. When both ionophores were added together, the stimulation was increased up to 2.7-fold. When a potassium concentration gradient (high K+ in) was applied to the proteoliposome membrane, a significant drop in the CCCP-stimulated ATPase activity was observed. Inversion of the K+ concentration gradient (high K+ out) did not decrease the stimulation by CCCP. High Na+ in also decreased the stimulation induced by CCCP in the absence but not in the presence of external K+. However, high Li+ in had no effect. Direct potassium efflux from the proteolyposomes was detected upon addition of MgATP using a selective K+ electrode. The ATP-dependent potassium efflux was abolished in CCCP and/or nigericin-pretreated proteoliposomes. However, during steady state ATP hydrolysis, a transient and small K+ efflux was observed upon addition of a CCCP pulse. I propose that the plasma membrane Mg2+-dependent ATPase in yeast cells not only carries out electrogenic H+ ejection but also drives the uptake of potassium via a voltage-sensitive gate which is closed in the absence and open in the presence of the membrane potential.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001203:Ascomycota / Q000201:enzymology*; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009550:Nigericin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011510:Proteolipids; D012568:Schizosaccharomyces / Q000201:enzymology*
chemical_list: D011510:Proteolipids; C020485:proteoliposomes; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D009550:Nigericin; D011188:Potassium