Lysophosphatidylcholine-activated, vanadate-inhibited, Mg2+-ATPase from radish microsomes

Plant lipid environment and membrane enzymes: the case of the plasma membrane H+-ATPase

Several lipid classes constitute the universal matrix of the biological membranes. With their amphipathic nature, lipids not only build the continuous barrier that confers identity to every cell and organelle, but they are also active actors that modulate the activity of the proteins immersed in the lipid bilayer. The plasma membrane H(+)-ATPase, an enzyme from plant cells, is an excellent example of a transmembrane protein whose activity is influenced by the hydrophilic compartments at both sides of the membrane and by the hydrophobic domains of the lipid bilayer. As a result, an extensive documentation of the effect of numerous amphiphiles in the enzyme activity can be found. Detergents, membrane glycerolipids, and sterols can produce activation or inhibition of the enzyme activity. In some cases, these effects are associated with the lipids of the membrane bulk, but in others, a direct interaction of the lipid with the protein is involved. This review gives an account of reports related to the action of the membrane lipids on the H(+)-ATPase activity.

Enhanced ATP-dependent copper efflux across the root cell plasma membrane in copper-tolerant Silene vulgaris

We studied copper uptake in inside-out plasma membrane vesicles derived from roots of copper-sensitive, moderately copper-tolerant and highly copper-tolerant populations of Silene vulgaris (Amsterdam, Marsberg and Imsbach, respectively). Plasma membrane vesicles were isolated using the two-phase partitioning method and copper efflux was measured using direct filtration experiments. Vesicles derived from Imsbach plants accumulated two and three times more copper than those derived from Marsberg and Amsterdam plants, respectively. This accumulation was ATP-dependent. Also, 9-amino-6-chloro-2-methoxyacridine fluorescence quenching rates upon copper addition decreased in the order Imsbach>Marsberg>Amsterdam. Our results support the hypothesis that efflux of copper across the root plasma membrane plays a role in the copper tolerance mechanism in S. vulgaris.

Proton-symport of L-valine in plasma membrane vesicles isolated from leaves of the wild-type and the Val(r)-2 mutant of Nicotiana tabacum L

Transport of amino acids across the plasma membranes of various cell types is a key process in controlling the nitrogen balance of leaves. We studied the transport of the neutral amino acid L-valine into plasma membrane vesicles obtained by aqueous polymer two-phase partitioning of a microsomal fraction isolated from leaves of the wild-type and the Val(r)-2 mutant of tobacco (Nicotiana tabacum L.). Initial influxes were determined after the imposition of a pH-gradient (DeltapH, inside alkaline) and/or an electrical gradient (Deltapsi, inside negative) across the vesicle membrane. The initial magnitudes of the imposed gradients were DeltapH=2 and Deltapsi=-68 mV. In vesicles from the wild-type, the DeltapH-dependent valine influx could be analysed into a high-affinity (Km approximately 20 microM) and a low-affinity (Km approximately 3 mM) component. The influx of valine by the low-affinity system was stimulated about twofold, and that by the high-affinity system more than sixfold by the imposition of Deltapsi. This strong stimulation of the high-affinity system may indicate that it transports 2H+/amino acid. In the Val(r)-2 mutant the high-affinity component appeared to be completely absent.

Transport of amino acids (L-valine, L-lysine, L-glutamic acid) and sucrose into plasma membrane vesicles isolated from cotyledons of developing pea seeds

Transport of the amino acids L-valine, L-lysine, and L-glutamic acid and of sucrose was studied in plasma membrane vesicles isolated from developing cotyledons of pea (Pisum sativum L. cv. Marzia). The vesicles were obtained by aqueous polymer two-phase partitioning of a microsomal fraction and the uptake was determined after the imposition of a H(+)-gradient (DeltapH, inside alkaline) and/or an electrical gradient (Deltapsi, inside negative) across the vesicle membrane. In the absence of gradients, a distinct, time-dependent uptake of L-valine was measured, which could be enhanced about 2-fold by the imposition of DeltapH. The imposition of Deltapsi stimulated the influx of valine by 20%, both in the absence and in the presence of DeltapH. Uptake of L-lysine was more strongly stimulated by Deltapsi than by DeltapH, and its DeltapH-dependent uptake was enhanced about 6-fold by the simultaneous imposition of Deltapsi. In the absence of gradients the uptake of L-glutamic acid was about 2-fold higher than that of L-valine, but it was not detectably affected by DeltapH or Deltapsi. Although the transport of sucrose was very low, a stimulating effect of DeltapH could be clearly demonstrated. The results lend further support to the contention that during seed development cotyledonary cells employ H(+)-symporters for the active uptake of sucrose and amino acids.

The plasma membrane H(+)-ATPase from yeast. Effects of pH, vanadate and erythrosine B on ATP hydrolysis and ATP binding

The H(+)-ATPase from the plasma membrane of Saccharomyces cerevisiae was isolated and purified. The rate of ATP hydrolysis and ATP binding was measured as a function of pH and the effect of the vanadate and erythrosine B inhibitors was investigated. The pH dependence of the rate of ATP hydrolysis forms a bell-shaped curve with a maximum at pH 6 and half-maximal rates at pH 5.0 and 7.4. Only the pH dependence between pH 6 and pH 7.6 is reversible. Above pH 7.6 and below pH 5.5, denaturation of the isolated enzyme is observed. The rate of ATP binding shows the same pH dependency as that of ATP hydrolysis. Both pH dependencies can be described by the dissociation of a monovalent acidic group with a pK of 7.4. It is concluded that the enzyme must be protonated before ATP binding. Vanadate does not inhibit ATP binding, ADP release or Pi release at concentrations where complete inhibition of ATP hydrolysis is observed. It is concluded that vanadate inhibits a step of the reaction cycle which occurs after Pi release. In contrast, erythrosine B inhibits ATP binding and thus affects the first step of the reaction cycle.

Purification and characterization of the proton translocating plasma membrane ATPase of red beet storage tissue

Plasma membranes were prepared from red beet (Beta vulgaris L.) storage tissue by partition in an aqueous two-phase system. A highly active proton-translocating ATPase was purified from these membranes by lysophosphatidylcholine extraction and glycerol density gradient centrifugation. The ATPase activity was inhibited by vanadate or dicyclohexyl carbodiimide, but was insensitive to azide, nitrate and molybdate at concentrations which inhibit the F1ATPase, the tonoplast ATPase, and acid phosphatase. Inhibition by vanadate was consistent with a non-competitive mechanism, with Ki = 10 microM. The Km for Mg-ATP was about 1 mM, magnesium ions were required, and the activity was stimulated by KCl and by lysophosphatidylcholine. The optimal pH was 6.5. The molecular mass by gel filtration in the presence of 2 g/liter octyl glucoside was 600 kDa, while dodecyl sulfate gel electrophoresis gave a polypeptide molecular mass of 100 kDa. After blotting onto nitrocellulose, the purified enzyme did not bind concanavalin A, although a concanavalin A-binding peptide of the plasma membrane runs to nearly the same position on the gel and showed some tendency to co-purify with the ATPase. Phospholipid vesicles into which the purified ATPase had been incorporated by the freeze-thaw technique showed vanadate-sensitive, ATP-dependent proton uptake. When the ATPase was reconstituted into lipid membranes at high protein to lipid ratios and incubated with ATP, two-dimensionally crystalline arrays of protein molecules were formed.

The plasma membrane ATPase of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. Purification and immunological relationships to F1-ATPases

The plasma-membrane-associated ATPase of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius characterized in a previous work [M. Lübben & G. Schäfer (1987) Eur. J. Biochem. 164, 533-540] has been solubilized. It can be easily removed from the membrane by mild treatment with zwitterionic detergents, therefore it appears to be a peripheral membrane protein analogous to the soluble F1-ATPase of eubacteria and eukaryotes. Further purification has been achieved by subsequent gel permeation and ion-exchange chromatography. The final purity is greater than 70% as judged by staining intensities after SDS/polyacrylamide gel electrophoresis. The ATPase consists of two major polypeptides of 65 kDa (alpha) and 51 kDa (beta) in comparable quantities; a minor band (20 kDa) is assumed to be a contaminant or a constitutive part of the enzyme, possibly copurified in substoichiometric amount. The native molecular mass of the solubilized ATPase determined by gel permeation is 430 kDa. Considering the precision of these methods, it remains open whether a 3:3 stoichiometry reflects the contribution of alpha and beta subunits to the quaternary structure, in analogy to known F1-ATPases. The catalytic properties resemble those of the membrane-bound state. There are two pH optima at 5.3 and 8.0 in the absence and only one optimum at 6.5 in the presence of the activating anion sulfite. Activity is strictly dependent on the divalent cations Mg2+ or Mn2+. ATP and dATP are hydrolyzed with highest rates; also other purine and pyrimidine nucleotides are cleaved significantly, but not ADP, pyrophosphate and p-nitrophenyl phosphate. The ATPase is insensitive to azide or vanadate but is inhibited by relatively low concentrations of nitrate. Polyclonal antisera have been raised against the beta subunit of the Sulfolobus ATPase. Cross-reactivities with cellular or membrane extracts of a number of archaebacteria, eubacteria and chloroplasts have been analyzed by means of Western blotting and immunodecoration. A strong cross-reactivity with other genera of the Sulfolobales is observed, also with Methanobacterium, Methanosarcina, Methanolobus and Halobacterium. Even membranes of the eubacterium Escherichia coli and of eukaryotic chloroplast react with the antibodies. With one exception, in all cases the molecular mass of the cross-reacting polypeptide falls in the range of 51-56 kDa. Only in Halobacterium halobium, bands at 66 and 68 kDa have been detected. In order to identify the cross-reacting polypeptides, the purified F1-ATPases of E. coli, chloroplasts and beef heart mitochondria have been tested.(ABSTRACT TRUNCATED AT 400 WORDS)

A plasma-membrane associated ATPase from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius

Thermoacidophilic archaebacteria have gained much interest because of their phylogenetic distance to eubacteria and eukaryotes and also because of their unique living conditions. Investigation of the energy-converting system therefore offers a key for understanding the evolutionary position and environmental adaptation of these unusual bacteria. A plasma-membrane-associated adenosine triphosphatase with specific activities of 0.3-0.6 mumol min-1 (mg protein)-1 has been detected in the thermoacidophilic archaebacterium Sulfolobus acidocaldarius (DSM 639). The enzyme exhibits two optima at pH 5.5 and 8.0, sulfite activation leads to only one optimum at pH 6.25. In the presence of the divalent cations Mg2+ or Mn2+ it hydrolyzes ATP with highest reactivity and also other purine and pyrimidine nucleotides, but not ADP and pyrophosphate. A specific stimulation by monovalent cations is not observed. The ATPase activity is not inhibited by N,N'-dicyclohexylcarbodiimide, azide or vanadate, but it is by the vascular ATPase inhibitor nitrate with an [I]50 of 8 mM. Linear Arrhenius plots up to 75 degrees C reflect pronounced adaptation to the hot environment of the archaebacterium. The solubilized ATPase as localized by activity staining in non-denaturating gels and further analyzed by sodium dodecyl sulfate electrophoresis is composed of two major polypeptides of 65 and 51 kDa reminiscent of the alpha and beta subunits of eubacterial and eukaryotic F0F1-ATPases. The ATPase is suggested as a probable candidate for a reversibly acting ATP synthase responsible for oxidative phosphorylation found in Sulfolobus acidocaldarius.

Fusicoccin stimulates the H+-ATPase of plasmalemma in isolated membrane vesicles from radish

The effect of fusicoccin on the plasmalemma H+-ATPase has been investigated in a membrane fraction from 24 h old radish seedlings, in which Mg:ATP-dependent H+-transport is mediated only by the plasmalemma H+-ATPase. Fusicoccin stimulated the plasmalemma H+-ATPase - i.e. Mg:ATP-dependent intravesicular acidification, hyperpolaryzation of delta psi and ATPase activity -, when these activities were measured at the physiologically relevant pHs of 7.3 to 7.6. No effect of FC on the plasmalemma H+-ATPase was evident at pH 6.6.

Partial purification and characterization of an anion-activated ATPase from radish microsomes

Previous investigation showed two distinct ATP-dependent proton-transporting systems in microsomal vesicle from radish seedlings, one inhibited by vanadate and one inhibited by NO-3. On the bases of the effects of these inhibitors we could discriminate two distinct ATPase activities in the same material. The NO-3 sensitive activity was separated from the vanadate-sensitive activity and partially purified by a single-step chromatographic method, which lead to approx 35-fold purification from the microsomes and to a specific activity of 2.3 mumol Pi X min-1 X mg protein-1, at 30 degrees C. The partially purified activity was specific for ATP, some activity being observed toward GTP, and even less toward CTP, UTP and ITP. No significant Pi hydrolysis was found with ADP, AMP, p-nitrophenylphosphate and glucose 6-phosphate. ADP but not AMP was inhibiting in the presence of ATP. The activity was dependent on divalent cations in the order of preference: Mg2+ greater than Mn2+ greater than Co2+ greater than Ca2+ greater than Zn2+. The activity was unaffected by monovalent cations, strongly activated by Cl-, inhibited by 90% by 50 mM NO-3, virtually unaffected by oligomycin and NaN3. At least 90% of the activity was abolished in the presence of each: 10 microM N,N'-dicyclohexylcarbodiimide, 10 microM erythrosin B, 10 mu mersalyl, 100 microM trimethyltin, 100 microM diethylstilbestrol, 100 microM N-ethylmaleimide. No inhibition has been found in the presence of Ca2+, at a concentration blocking the vanadate-sensitive activity. Nigericin, gramicidin and carbonylcyanide p-trifluoromethoxyphenylhydrazone stimulated the activity of this preparation after it was incubated in the presence of sonicated phospholipids, suggesting the capacity of the ATPase to function as a H+-transporting system. All characteristics mentioned were closely similar to those described in the vacuolar ATPases.