Biomedical subjects

E Zakharyan

Publications and source records attributed to E Zakharyan.

3 recordsLinked to original sources

PubMed2001

K+ influx by Kup in Escherichia coli is accompanied by a decrease in H+ efflux.

Escherichia coli accumulates K+ by means of multiple uptake systems of which Kup is the major transport system at acidic pH. In cells grown under fermentative conditions at pH 5.5, K+ influx by a wild-type strain upon hyper-osmotic stress at pH 5.5 was accompanied by a marked decrease in H+ efflux, with a 1:1 ratio of K+ to H+ fluxes. This was observed with cells treated with N,N'-dicyclohexylcarbodiimide. Similar results with a mutant defective in Kdp and TrkA but with a functional Kup system but not in a mutant defective in Kdp and Kup but having an active TrkA system suggest that Kup operates as a H+ -K+ -symporter.

Adenosine Triphosphatases↗

PubMed1998

Relationship of the Escherichia coli TrkA system of potassium ion uptake with the F0F1-ATPase under growth conditions without anaerobic or aerobic respiration.

K+ uptake by the Escherichia coli TrkA system is unusual in that it requires both ATP and deltamuH+; a relation with H+ circulation through the membrane is therefore suggested. The relationship of this system with the F0F1-ATPase was studied in intact cells grown under different conditions. A significant increase of the N,N'-dicyclohexylcarbodiimide(DCCD)-inhibited H+ efflux through the F0F1 by 5 mM K+, but not by Na+ added into the potassium-free medium was revealed only in fermenting wild-type or parent cells, that were grown under anaerobic conditions without anaerobic or aerobic respiration and with the production of H2. Such an increase disappeared in the deltaunc or the trkA mutants that have altered F0F1 or defective TrkA, respectively. This finding indicates a closed relationship between TrkA and F0F1, with these transport systems being associated in a single mechanism that functions as an ATP-driven H(+)-K(+)-exchanging pump. A DCCD-inhibited H(+)-L(+)-exchange through these systems with the fixed stoichiometry of H+ and K+ fluxes (2H+/K+) and a higher K+ gradient between the cytoplasm and the external medium were also found in these bacteria. They were not observed in cells cultured under anaerobic conditions in the presence of nitrate or under aerobic conditions with respiration and without production of H2. The role of anaerobic or aerobic respiration as a determinant of the relationship of the TrkA with the F0F1 is postulated. Moreover, an increase of DCCD-inhibited H+ efflux by added K+, as well as the characteristics of DCCD-sensitive H(+)-K(+)-exchange found in a parent strain, were lost in the arcA mutant with a defective Arc system, suggesting a repression of enzymes in respiratory pathways. In addition, K+ influx in the latest mutant was not markedly changed by valinomycin or with temperature. The arcA gene product or the Arc system is proposed to be implicated in the regulation of the relationship between TrkA and F0F1.

Aerobiosis↗

PubMed1998

Regulation of intracellular pH and proton-potassium exchange in fermenting Escherichia coli grown anaerobically in alkaline medium.

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.

Anaerobiosis↗