K+ uptake by fermenting Escherichia coli cells: pH dependent mode of the TrkA system operating.
Escherichia coli accumulates K+ by means of multiple transport systems, of which TrkA is the most prominent at neutral and alkaline pH while Kup is major at acidic pH. In the present study, K+ uptake was observed with cells grown under fermentative conditions at an initial pH of 9.0 and 7.3 (the medium pH decreased to 8.4 and 6.8, respectively, during the mid-logarithmic growth phase), washed with distilled water and resuspended in a K+ containing medium at pH 7.5 in the presence of glucose. The kinetics for this K+ uptake and the amount of K+ accumulated by the wild type and mutants having a functional TrkA or Kup could confirm that K+ uptake by E. coli grown either at pH 9.0 or pH 7.3 occurs mainly through TrkA. The following results distinguish pH dependent mode of TrkA operating: (1) K+ uptake was inhibited by DCCD in cells grown either at pH 9.0 or pH 7.3, although the stoichiometry of K+ influx to DCCD-inhibited H+ efflux for bacteria grown at pH 9.0 varied with external K+ concentration, but remained constant for cells grown at pH 7.3; (2) K+ uptake was observed with an atpD mutant grown at pH 9.0 but not at pH 7.3; (3) The DCCD-inhibited H+ efflux was increased 8-fold less by 5 mM K+ added into a K+ free medium for bacteria grown at pH 9.0 than that for cells grown at pH 7.3; (4) the DCCD-inhibited ATPase activity of membrane vesicles from bacteria grown at pH 9.0 was reduced a little in the presence of 100 mM K+, but stimulated more than 2.4-fold at pH 7.3.
Trchounian
A
A
Faculty of Pharmaceutical Sciences, Chiba University, Japan. Trchounian@ysu.am
Kobayashi
H
H
D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D008567:Membranes, Artificial; D009154:Mutation; D011188:Potassium / Q000493:pharmacokinetics*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020917:Receptor, trkA
D002352:Carrier Proteins; D008565:Membrane Proteins; D008567:Membranes, Artificial; D004024:Dicyclohexylcarbodiimide; D020917:Receptor, trkA; D006180:Proton-Translocating ATPases; D011188:Potassium