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 ΔμH; a relation withH+ circulation through the membrane is thereforesuggested. The relationship of this system with the F0F1-ATPase was studied in intact cells grownunder different conditions. A significant increase of the N,N'-dicyclohexylcarbodiimide(DCCD)-inhibitedH+ efflux through the F0F1 by 5 mMK+, but not by Na+ added into thepotassium-free medium was revealed only in fermenting wild-type orparent cells, that were grown under anaerobic conditions withoutanaerobic or aerobic respiration and with the production of H2. Such an increase disappeared in the Δunc or the trkA mutants that have alteredF0F1 or defective TrkA, respectively. This finding indicates a closed relationship between TrkA andF0F1, with these transport systems beingassociated in a single mechanism that functions as an ATP-driven H+–K+-exchanging pump. ADCCD-inhibited H+–K+-exchangethrough these systems with the fixed stoichiometry of H+and K+ fluxes(2H+/K+) and a higherK+ gradient between the cytoplasm and the externalmedium were also found in these bacteria. They were not observed incells cultured under anaerobic conditions in the presence of nitrate orunder aerobic conditions with respiration and without production of H2. The role of anaerobic or aerobic respiration as adeterminant of the relationship of the TrkA with the F0F1 is postulated. Moreover, an increase of DCCD-inhibited H+ efflux by added K+, aswell as the characteristics of DCCD-sensitiveH+–K+-exchange found in a parentstrain, were lost in the arcA mutant with a defective Arc system, suggesting a repression of enzymes in respiratorypathways. In addition, K+ influx in the latest mutantwas not markedly changed by valinomycin or with temperature. The arcA gene product or the Arc system is proposed to beimplicated in the regulation of the relationship between TrkA and F0F1.

Relationship of potassium ion transport and ATP synthesis in pea cotyledon mitochondria

Simultaneous monitoring of ATP synthesis and K+ movements across pea mitochondrial membranes revealed information about the competition of the two processes for mitochondrial energy. In the presence of valinomycin and at low extramitochondrial K+ concentration, ADP could be phosphorylated rapidly. This occurred with a decrease in net potassium ion uptake. At higher external K+ concentrations respiratory energy was unavailable for ATP synthesis and only a portion of added ADP could be phosphorylated within a reasonable time. Magnesium ions were shown to have an inhibitory effect on the K+ uptake, and stimulated a greater rate of ATP synthesis. When valinomycin and ADP were added simultaneously so that phosphorylation of the ADP and enhancement of K+ uptake could compete for mitochondrial energy, K+ uptake was preferred over ATP synthesis.

The effect of diffusible acids on potassium ion uptake by yeast

1. When yeast oxidizes ethanol at different pH values the uptake of K+ corresponds closely to the amount of acetate accumulated at each pH value. 2. The addition of semicarbazide to the suspension buffered at pH4.75 inhibited both the K+ uptake and the acetate accumulation by about 50%. 3. The addition of either acetate or propionate to the suspensions markedly increased the K+ uptake. 4. The addition of acetate to the suspensions lowered the intracellular pH of the yeast from a resting value of pH5.80 to 5.56. 5. The ratio of the initial rate of K+ uptake to O2 consumption was 0.77. This ratio was increased to 1.77 in the presence of 10mmol of propionate/l.