Potassium transport in Escherichia coli. Evidence for a K+-transport adenosine-5'-triphosphatase

Osmoregulation inBacillus subtilisunder potassium limitation: a new inducible K+-stimulated, VO43–-inhibited ATPase

Bacillus subtilis exhibited an inducible K+-transporting ATPase activity with apparent Kmand maximum velocity Vmaxof 12.9 µM and 25.1 µmol·min–1·(g cell protein)–1, respectively, when cultivated on a synthetic medium containing less than 400 µM K+. Due to this enzyme, the growth rate of the bacterium in synthetic medium was not changed down to 115 µM K+, and the bacterium was able to grow down to 20 µM K+. The limiting K+concentration was higher in media with osmolarity increased by NaCl or sucrose. The ATPase was inhibited by micromolar concentrations of vanadate (Ki= 1.6 µM). The ATPase activity was not stimulated by any other monovalent cation. The subunit of this ATPase, with an Mrof 52 000, covalently bound the gamma phosphate group of ATP. This phosphorylated intermediate was unstable in neutral and basic pH as well as in the presence of potassium and was stable in acid pH. The enzyme did not show immunological cross-reactivity with antibody against Kdp ATPase of Escherichia coli.Key words: Kdp-like, potassium transport, Bacillus subtilis, transport ATPase, P-type ATPase.

ATP-driven potassium transport in right-side-out membrane vesicles via the Kdp system of Escherichia coli

The ATP-generating system described by Hugenholtz, J., Hong, J.-S. and Kaback, H.R. ((1981) Proc. Natl. Acad. Sci. USA 78, 3446-3449) has been used to synthesize ATP up to 1.8 mM in right-side-out membrane vesicles from Escherichia coli. This ATP level was sufficient to drive uptake of potassium ions via the Kdp-ATPase. In the kdp wild type strain about 110 nmoles K+/mg membrane protein were accumulated. This process was still partially sensitive to the well-known inhibitors of P-type ATPases, orthovanadate and bafilomycin B1.

The phosphorylation site of the Kdp-ATPase of Escherichia coli: site-directed mutagenesis of the aspartic acid residues 300 and 307 of the KdpB subunit

The potassium-translocating Kdp-ATPase of Escherichia coli shares common functional properties with eukaryotic P-type ATPases. The KdpB subunit has been identified as the catalytic subunit forming the phosphorylated intermediate. Substitution of Asp-307 in KdpB by Glu, Asn, Gln, Tyr, His, Ala or Ser by site-directed mutagenesis and the subsequent transfer of the point mutations to the chromosome revealed that the mutants were not functioning with respect to cell growth at low K+ concentrations and ATPase activity as well as phosphorylation capacity of the purified Kdp complex. These findings indicate that Asp-307 in KdpB is the phosphorylation site of the Kdp-ATPase. In contrast, replacement of the close but non-conserved Asp-300 by Asn or Glu has no immediate influence on the enzyme functions tested. However, the Km for K+ of the ATPase activity has been increased 30-fold compared with the wild-type enzyme.

Isolation and characterization of the high-affinity K(+)-translocating ATPase from Rhodobacter sphaeroides

Cells of the purple nonsulfur bacterium Rhodobacter sphaeroides express a high-affinity K+ uptake system when grown in media with low K+ concentrations. A vanadate-sensitive, K(+)-stimulated and Mg(2+)-stimulated ATPase was purified from membranes of these cells by solubilization with decyl-beta-D-maltoside in the presence of Escherichia coli phospholipids followed by triazine-dye affinity chromatography. This primary transport system has a substrate specificity and an inhibitor sensitivity closely similar to those of the Kdp ATPase from E. coli and is composed of three subunits with molecular masses of 70.0, 43.5, and 23.5 kDa.

Characterization of the membrane-bound ATPase from a facultatively anaerobic alkalophile

We have studied the properties of membrane-bound ATPase of a facultatively anaerobic alkalophile. The enzyme could not be solubilized without detergent, suggesting an integral membrane protein. The activity was accelerated by NH4+ and acetate anion, and inhibited by NH3-. The enzyme required Mg2+ or Mn2+ as a divalent cation for the maximal activity. In addition to ATP, the enzyme utilized other triphosphates of nucleosides as a substrate, but not di- nor monophosphates. The enzyme was suggested to crossreact with an antibody against the alpha-subunit of Na+/K+-ATPase from dog kidney.

The high-affinity K+-translocating ATPase complex from Bacillus acidocaldarius consists of three subunits

Cells of the thermoacidophilic bacterium Bacillus acidocaldarius express a high-affinity K+-uptake system when grown at low external K+. A vanadate-sensitive, K+- and Mg2+-stimulated ATPase was partially purified from membranes of these cells by solubilization with a non-ionic detergent followed by ion-exchange chromatography of the extract. Combinations of non-denaturing and denaturing electrophoretic separation methods revealed that the ATPase complex consisted of three subunits with molecular weights almost identical to those of the KdpA, B and C proteins, which together form the Kdp high-affinity, K+-translocating ATPase complex of Escherichia coli. The affinity of the partially purified ATPase from B. acidocaldarius for its substrates K+ (Km 2-3 microM) and ATP (Km 80 microM), its stimulation by various divalent cations, and its inhibition by vanadate (Ki 1-2 microM), bafilomycin A1 (Ki 20 microM), DCCD (Ki 200 microM) or Ca2+ were also similar to those of the E. coli enzyme, indicating that the two K+-translocating ATPases have almost identical properties.

The K+-translocating Kdp-ATPase from Escherichia coli. Purification, enzymatic properties and production of complex- and subunit-specific antisera

The Kdp system from Escherichia coli is a derepressible high-affinity K+-uptake ATPase. Its membrane-bound ATPase activity was approximately 50 mumol g-1 min-1. The Kdp-ATPase complex was purified from everted vesicles by solubilization with the nonionic detergent Aminoxid WS 35 followed by DEAE-Sepharose CL-6B chromatography at pH 7.5 and pH 6.4 and gel filtration on Fractogel TSK HW-65. The overall yield of activity was 6.5% and the purity at least 90%. The isolated KdpABC complex had a high affinity for its substrates K+ (Km app. = 10 microM) and Mg2+-ATP (Km = 80 microM) and a narrow substrate specificity. The ATPase activity was inhibited by vanadate (Ki = 1.5 microM), fluorescein isothiocyanate (Ki = 3.5 microM), N,N'-dicyclohexylcarbodiimide (Ki = 60 microM) and N-ethylmaleimide (Ki = 0.1 mM). The purification protocol was likewise applicable to the isolation of a KdpA mutant ATPase which in contrast to the wild-type enzyme exhibited an increased Km value for K+ of 6 mM and a 10-fold lowered sensitivity for vanadate. Starting from the purified Kdp complex the single subunits were obtained by gel filtration on Bio-Gel P-100 in the presence of SDS. Both the native Kdp-ATPase and the SDS-denatured polypeptides were used to raise polyclonal antibodies. The specificity of the antisera was established by immunoblot analysis. In functional inhibition studies the anti-KdpABC and anti-KdpB sera impaired ATPase activity in the membrane-bound as well as in the purified state of the enzyme. In contrast, the anti-KdpC serum did not inhibit enzyme activity.

Energy efficiency of different mechanistic models for potassium ion uptake in lower eukaryotic cells

Different mechanistic models for potassium ion uptake are analyzed by an equilibrium-thermodynamic formalism in terms of their comparative efficiency in setting chemical potential differences of the potassium ion of different magnitudes across the plasma membrane of lower eukaryotic cells. The possible adaptive advantages for a multimode mechanism(s) operating in alternative modes depending on the physiological and/or environmental conditions of the cells are discussed.

Energetic consequences of two mutations in Escherichia coli K+ uptake systems for growth under potassium-limited conditions in the chemostat

The energetics of growth of two Escherichia coli strains (TK 2240 and TK 2242) differing in Km of the high-affinity potassium uptake system and lacking the low-affinity system were studied in the chemostat under potassium-limited conditions. The results were compared with the results obtained previously (Mulder, M.M., Teixeira de Mattos, M.J., Postma, P.W. and Van Dam, K. (1986) Biochim. Biophys. Acta 851, 223-228) with the wild-type FRAG-1, having two potassium uptake systems, and FRAG-5, a mutant which lacks the high-affinity potassium uptake system. We postulated that the high-affinity potassium uptake system was able to generate such a steep gradient across the membrane that the low-affinity system would act in reverse, thus creating a futile cycle of potassium ions at the cost of energy. As a result, FRAG-1 would show a higher ATP turnover at all growth rates tested than the mutant FRAG-5, in which strain the proposed futile cycle is interrupted because of the lack of the high-affinity system. It is shown here that the results obtained with TK 2240 and TK 2242 are in line with our hypothesis of futile potassium cycling. Under our experimental conditions, the yield on potassium was not dependent on the kinetic parameters of the uptake systems. The (thermodynamic) energy demand of the uptake systems determined the carbon substrate conversion required to achieve this yield.

Sodium ion transport decarboxylases and other aspects of sodium ion cycling in bacteria

Images

High-affinity potassium uptake system in Bacillus acidocaldarius showing immunological cross-reactivity with the Kdp system from Escherichia coli

During growth with low levels of K+, Bacillus acidocaldarius expressed a high-affinity K+ uptake system. The following observations indicate that this system strongly resembles the Kdp-ATPase of Escherichia coli: (i) its high affinity for K+ (Km of 20 microM or below); (ii) its poor transport of Rb+; (iii) the enhanced ATPase activity of membranes derived from cells grown with low levels of K+ (this activity was stimulated by K+ and inhibited by vanadate); (iv) the expression of an extra protein with a molecular weight of 70,000 in cells grown with low levels of K+; and (v) the immunological cross-reactivity of this 70,000-molecular-weight protein with antibodies against the catalytic subunit B of the E. coli Kdp system. Antibodies against the complete E. coli Kdp system, which immunoprecipitated the whole E. coli KdpABC complex, almost exclusively precipitated the 70,000-molecular-weight protein from detergent-solubilized B. acidocaldarius membranes. The possibility that the B. acidocaldarius Kdp system consists of a single, KdpB-type subunit is discussed.

Sodium-stimulated ATPase in Streptococcus faecalis

We measured Na+-stimulated ATPase activity in a mutant of Streptococcus faecalis defective in the generation of proton motive force. The activity in membrane vesicles was 62.1 +/- 5.9 nmol of phosphate produced per min per mg of protein when cells were grown on medium containing 0.12 M Na+. Activity decreased as the concentration of Na+ in the growth medium decreased. The decrease in enzyme activity corresponded to the decrease in transport activity for Na+ in both whole cells and membrane vesicles. The effects of pH on both activities were identical. Thus, it is suggested that Na+ movement is mediated by this enzyme. Sodium extrusion and ATPase activity in the wild-type strain were markedly lower than those observed in the mutant strain. Elevated activities of both Na+ extrusion and Na+-stimulated ATPase could be detected in the wild-type strain when cells were grown in the absence of proton motive force. Thus, we propose that the level of ATPase is increased by dissipation of the proton motive force.

Opening of potassium channels in Escherichia coli membranes by thiol reagents and recovery of potassium tightness

The retention of high potassium levels in Escherichia coli is not dependent on intact energy metabolism, since without the presence of a carbon source or in the presence of energy inhibitors significant K+ gradients can be maintained. In contrast, with 0.5 mM N-ethylmaleimide, K+ depletion is immediate and complete. As a final result, intracellular K+ is approximately three times more concentrated than the K+ in the medium. Increase of K+ in the medium is immediately followed by K+ uptake whereas in the unpoisoned state only an increase in the osmotic pressure of the medium would result in an increase of the K+ pool. The intracellular K+ undergoes continuous turnover in the poisoned cells whereas in intact cells turnover is strictly dependent on the presence of a metabolizable carbon source. After removal of the thiol reagent the cell recovers its capacity to concentrate potassium. The recovery process is inhibited by energy inhibitors or by incubation at low temperature but not by chloramphenicol. It is only slightly slowed down by carbon or sulfur starvation. The leak provoked by N-ethylmaleimide is similar in wild-type E. coli cells when a derepressed kdp uptake system working in the micromolar range of the K+ concentration is responsible for the intracellular pool of K+ and when, in a medium millimolar K+ concentration range, the trkA and trkD systems are predominant.

Temperature-dependent relationship between K+ influx, Mg2+-ATPase activity, transmembrane potential and membrane lipid composition in mycoplasma

The temperature-dependent relationship between K+ active influx, Mg2+-ATPase activity, transmembrane potential (delta psi) and the membrane lipid composition has been investigated in mycoplasma PG3. Native organisms were grown in a medium containing 10 microgram/ml cholesterol and either oleic plus palmitic (chol (+), O + P) or elaidic (chol (+), E) acids. Adapted cells were grown in a medium free of exogenous cholesterol and supplemented with elaidic acid (chol (-), E). Arrhenius plots of 42K+ active influx gave a linear relationship for (chol (+), O + P) cells (EA = -9 kcal). On the other hand, when oleic plus palmitic acids are replaced by elaidic acid, an upward discontinuity appears between 28 and 30 degrees C, which is associated with a large increase in the apparent activation energy of the process (t > 30 degrees C, EA = -24 kcal; t < 30 degrees C, EA = -40 kcal). Finally, a biphasic response with a break at approx. 23 degrees C (EA = -7 kcal, t > 23 degrees C; EA = -44 kcal, t < 23 degrees C) is observed for (chol(-), E) organisms. From the lack of correspondence between these effects on the K+ influx and the temperature dependence of both the Mg2+-ATPase activity and delta psi, it is suggested that changes in the membrane lipid composition affect the K+ transport at the level of the K+ carrier itself. Differential scanning calorimetry, steady-state fluorescence polarization of diphenylhexatriene and freeze-fracture electron microscopy experiments further suggest that the effect is largely due to modifications of the membrane microviscosity and that the K+ carrier is associated with the most fluid lipid species present in the membrane.