title: Regulation of intracellular pH and proton-potassium exchange in fermenting Escherichia coli grown anaerobically in alkaline medium.
abstract: Fermenting Escherichia coli wild type cells, grown anaerobically at alkaline pH (pH 8.3-8.6), upon transfer into the medium at pH 7.5-7.8 were shown to maintain intracellular pH at 7.5, acidify medium, take in K+, generate membrane potential of -160 mV and produce molecular hydrogen. Proton-potassium exchange proceeded in one step, was inhibited by the N,N'-dicyclohexylcarbodiimide (DCCD) and protonophore CCCP. H+ secretion was sensitive to osmotic shock, and K+ uptake up to the potassium gradient between the cytoplasm and the medium of more than 2 x 10(3) occurred at Km 3.0 mM and was carried out upon upshock or downshock. The stoichiometry of DCCD-inhibited cation fluxes was unstable upon change of experimental conditions. This H+,K+ exchange was not observed in E. coli mutants with the defect in the alpha-subunit of H(+)-ATPase F0F1 complex (uncA) or in the TrkA system of K+ uptake (trkA trkD). The DCCD-inhibited ATPase activity of membrane vesicles did not show any significant dependence on K+ activity in the medium. We suggest that proton and potassium transport systems are involved in the regulation of intracellular pH in E. coli. K+ uptake in the bacteria grown anaerobically at alkaline pH is carried out by the TrkA system, which functions as uniporter, interacts with the F0F1 proton pump by means of transmembrane electrochemical gradient for H+ which is used as the driving force. Growth medium pH, probably, determines the character of interaction of the TrkA with the F0F1.
authors.affiliation: Yerevan State University, Department of Biophysics, Republic of Armenia.
authors.forename: A
authors.initials: A
authors.lastname: Trchounian
authors.forename: E
authors.initials: E
authors.lastname: Ohanjayan
authors.forename: E
authors.initials: E
authors.lastname: Zakharyan
mesh_terms: D000693:Anaerobiosis; D017920:Antiporters / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D003470:Culture Media / Q000494:pharmacology; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000737:chemistry*; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009997:Osmotic Pressure; D011188:Potassium / Q000378:metabolism*; D027961:Potassium-Hydrogen Antiporters; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020917:Receptor, trkA
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003470:Culture Media; D008565:Membrane Proteins; D027961:Potassium-Hydrogen Antiporters; D004024:Dicyclohexylcarbodiimide; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D006859:Hydrogen; D020917:Receptor, trkA; D006180:Proton-Translocating ATPases; D011188:Potassium