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1.
The influence of metallic, cations (added at 10 μM-1 mM) on the uptake of orthophosphate from 0.2–10 μM solution by Synechococcus leopoliensis (Racib.) Komarek was investigated. All cations tested except Mg2+ and Zn2+ stimulated phosphate uptake. The most pronounced stimulation of phosphate uptake was caused by Ca2+·Ca2+ markedly decreased the half-saturation concentration for orthophosphate uptake, apparently by acting upon the metabolic processes of phosphate transport into the cell. Phosphate did not influence Ca2+ fluxes across the cell-surface. 相似文献
2.
Rochelle D. Schwartz Joseph P. Wagner Xiao Yu David Martin 《Journal of neurochemistry》1994,62(3):916-922
Abstract: The effects of the divalent cations Ca2+, Sr2+, Ba2+, Mg2+, Mn2+, and Cd2+ were studied on γ-aminobutyric acidA (GABAA) responses in rat cerebral cortical synaptoneurosomes. The divalent cations produced bidirectional modulation of muscimol-induced 36Cl? uptake consistent with their ability to permeate and block Ca2+channels. The order of potency for inhibition of muscimol responses was Ca2+ > Sr2+ > Ba2+, similar to the order for permeation of Ca2+ channels in neurons. The order of potency for enhancement of muscimol responses was Cd2+> Mn2+ > Mg2+, similar to the order for blockade of Ca2+channels in neurons. Neither Ca2+ nor Mg2+ caused accumulation of GABA in the extravesicular space due to increased GABA release or decreased reuptake of GABA by the synaptoneurosomes. The inhibition of muscimol responses by Ca2+ was most likely via an intracellular site of action because additional inhibition could be obtained in the presence of the Ca2+ ionophore, A23187. This confirms electrophysiologic findings in cultured neurons from several species. In contrast, the effects of Cd2+, Mn2+, and Mg2+ may be mediated via blockade of Ca2+ channels or by intracellular sites, although the results of these studies do not distinguish between the two loci. The effects of Zn2+ were also studied, because this divalent cation is reported to have widely divergent effects on GABAA responses. In contrast to other studies, we demonstrate that Zn2+ inhibits GABAA responses in an adult neuronal preparation. Zn2+ produced a concentration-dependent inhibition (limited to 40%) of muscimol responses with an EC50 of 60 μM. The inhibition of muscimol-induced 38Cl? uptake by Zn2+ was noncompetitive. The effect of Zn2+was reduced in the presence of Mg2+ in a competitive or allosteric manner. The portion of GABAA receptors sensitive to Zn2+ may reflect a specific subunit composition in cerebral cortex as previously observed for recombinant GABAA receptors in several expression systems. The modulation of GABAA receptor function by Ca2+ and other divalent cations may play an important role in the development and/or attenuation of neuronal excitability associated with pathologic conditions such as seizure activity and cerebral ischemia. 相似文献
3.
Bisphosphonates (BPs) are drugs widely used in the treatment of various bone diseases. BPs localize to bone mineral, and their
concentration in resorption lacunae could reach almost milimolar levels. Bone alkaline phosphatase (ALP) is a membrane-bound
exoenzyme that has been implicated in bone formation and mineralization. In this study, we investigated the possible direct
effect of three N-containing BPs (alendronate, pamidronate, and zoledronate) on the specific activity of bone ALP obtained
from an extract of UMR106 rat osteosarcoma cells. Enzymatic activity was measured by spectrophotometric detection of p-nitrophenol product and by in situ visualization of ALP bands after an electrophoresis on cellulose acetate gels. Because ALP is a metalloprotein that contains
Zn2+ and Mg2+, both of which are necessary for catalytic function, we also evaluated the participation of these divalent cations in the
possible effect of BPs on enzymatic activity. All BPs tested were found to dose-dependently inhibit spectrophotometrically
measured ALP activity (93–42% of basal) at concentrations of BPs between 10−5
M and 10−4
M, the order of potency being zoledronate ≊ alendronate > pamidronate. However, coincubation with excess Zn2+ or Mg2+ completely abolished this inhibitory effect. Electrophoretic analysis rendered very similar results: namely a decrease in
the enzymatic activity of the bone-ALP band by BPs and a reversion of this inhibition by divalent cations. This study shows
that N-containing BPs directly inhibit bone-ALP activity, in a concentration range to which this exoenzyme is probably exposed
in vivo. In addition, this inhibitory effect is most possibly the result of the chelation of Zn2+ and Mg2+ ions by BPs. 相似文献
4.
John E. Bowen 《Plant and Soil》1987,99(1):115-125
Summary Excised roots of rice (Oryzae sativa L.) cv IR26 absorbed both Zn2+ and Cu2+ from 0.01 mM to 0.50 mM external solutions at rates twice those of cv M101 over a 30-min period. However, the latter have a two-fold greater affinity
(1/Km) for Zn2+ and Cu2+ than do those of the former. Zinc2+ and Cu2+ mutually and competitively inhibited uptake of each other, indicating that both micronutrient cations are absorbed through
the same uptake mechanism or carrier sites. Further, these differences in uptake rates are restricted to roots but they cannot
be explained by variations in root surface areas.
Excised roots of tomato (Lycopersicon esculentum L.) cv Kewalo absorbed Zn2+ and Cu2+ much more rapidly than did cv Sel 7625-2. Uptake of each cation was competitively and reciprocally inhibited by the other,
so Zn2+ and Cu2+ are seemingly accumulated through the same uptake system in tomato also. Tomato cultivars Kewalo and Sel 7625-2 did not differ
with regard to affinities of the root apices for Zn2+ and Cu2+; however. Vmax values for Zn2+ and Cu2+ uptake by roots of cv Kewalo were three-fold greater than those for cv Sel 7625-2.
Journal Series 2991 of the Hawaii Institute of Tropical Agriculture and Human Resources. Supported by USDA/CSRS Grants Program
in Tropical and Subtropical Agriculture (83-CSRS-2-2245). 相似文献
5.
Characterization of the Effects of Divalent Cations on the Coupled Activities of the H-ATPase in Tonoplast Vesicles 总被引:4,自引:2,他引:2
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The substrate requirement of the H+-ATPase in purified corn root tonoplast vesicles was investigated. The coupled activities, ATP hydrolysis and proton pumping, were simultaneously supported only by Mg2+ or Mn2+. The presence of Ca2+ or Ba2+ did not significantly affect the coupled activities. The addition of Cd2+, Co2+, Cu2+, and Zn2+ inhibited both the hydrolysis of Mg-ATP and the proton transport. However, the inhibition of proton pumping was more pronounced. Based on equilibrium analysis, both ATP-complexed and free forms of these cations were inhibitory. Inhibition of the hydrolysis of Mg-ATP could be correlated to the concentrations of the ATP-complex of Zn. On the other hand, the free Cu2+ and Co2+ were effective in inhibiting hydrolysis. For proton pumping, the ATP complexes of Co2+, Cu2+, and Zn2+ were effective inhibitors. However, this inhibition could be further modulated by free Co2+, Cu2+, and Zn2+. While the equilibrium concentrations of Cd-ATP and free Cd2+ were not estimated, the total concentration of this cation needed to inhibit the coupled activities of the H+-ATPase was found to be in the range of 10 to 100 micromolars. The presence of free divalent cations also affected the structure of the lipid phase in tonoplast membrane as demonstrated by the changes of emission intensity and polarization of incorporated 1,6-diphenyl-1,3,5-hexatriene. The differential inhibition caused by these cations could be interpreted by interactions with the protogenic domain of the membrane as previously proposed in “indirect-link” mechanism. 相似文献
6.
Tripositive-pyrophosphate [M(III)-PPi] complexes were used to investigate the role of free divalent cations on the membrane-bound pyrophosphatase. Divalent cations remain free and the M(III)-PPi complexes were employed as substrates. Formation of a La-PPi complex was studied by fluorescence, and the fact that Zn2+ and Mg2+ remain free in the solution was validated. Hydrolysis of La-PPi is stimulated by the presence of fixed concentrations of free Mg2+ or Zn2+ and this stimulation depends on the concentration of the cations when the La-PPi complex is fixed. The divalent cation stimulation order is Zn2+ > Co2+ > Mg2+ > Mn2+ > Ca2+ (at 0.5 mm of free cation). With different M(III)-PPi complexes, Zn2+ produces the same K
m, for all the complexes and Mg2+ stimulates with a different K
m. The results suggest that both Mg2+ and Zn2+ activate the membrane-bound pyrophosphatase but through different mechanisms. 相似文献
7.
Summary The toxicity of chromium and tin on growth, photosynthetic carbon-fixation, oxygen evolution, heterocyst differentiation and nitrogenase activity ofAnabaena doliolum and its interaction with bivalent cations has been studied. Some interacting cations, viz. Ca2+, Mg2+ and Mn2+, substantially antagonised the toxic effects of chromium and tin with reference to growth, heterocyst differentiation and nitrogenase activity in the following hierarchal sequence: Ca2+ > Mg2+ > Mn2+. However, the sequence of hierarchy was Mg2+ > Ca2+ > Mn2+ for carbon fixation and Mn2+ > Mg2+ > Ca2+ for photosynthetic oxygen evolution. Synergistically inhibitory patterns were noticed for all the parameters, viz. growth,14CO2 uptake, oxygen evolution, heterocyst differentiation and nitrogenase activity ofA. doliolum when Ni2+, Co2+ and Zn2+ were combined with the test metals in the growth medium. These cations followed the following sequence of synergistic inhibition: Ni2+ > Co2+ > Zn2+. Among all the interacting cations, Ca2+, Mg2+ and Mn2+ exhibited antagonistic effects which relieved the test cyanobacterium from metal toxicity. In contrast to this, Ni2+, CO2+ and Zn2+ showed synergistic inhibition which potentiating the toxicity of test metals in the N2-fixing cyanobacteriumA. doliolum. It is evident from the present study that bivalent cations, viz. Ca2+, Mg2+, Mn2+, Ni2+, Co2+ and Zn2+, may appreciably regulate the toxicity of heavy metals in N2-fixing cyanobacteria if present in aquatic media. 相似文献
8.
The relation that exist between the Pi-PPi exchange reaction and pyrophosphate hydrolysis by the membrane-bound pyrophosphatase of chromatophores ofRhodospirillum rubrum was studied. The two reactions have a markedly different requirement for pH. The optimal pH for hydrolysis was 6.5 while the Pi-PPi exchange reaction was at 7.5; the pH affects mainly theK
m
of Mg2+ or Pi for the enzyme; Mn2+ and Co2+ support the Pi-PPi exchange reaction partially (50%), but the reaction is slower than with Mg2+; other divalent cations like Zn2+ or Ca2+ do not support the exchange reaction. In the hydrolytic reaction, Zn2+, at low concentration, substitutes for Mg2+ as substrate, and Co2+ also substitutes in limited amount (50%). Other cations (Ca2+, Cu2+, Fe2+, etc.) do not act as substrates in complex with PPi. The Zn2+ at high concentrations inhibited the hydrolytic reaction, probably due to uncomplexed free Zn2+. In the presence of high concentration of substrate for the hydrolysis (Mg-PPi) the divalent cations are inhibitory in the following order: Zn2+>Mn2+>Ca2+Co2+>Fe2+>Cu2+>Mg2+. The data in this work suggest that H+ and divalent cations in their free form induced changes in the kinetic properties of the enzyme. 相似文献
9.
Flavio Flamigni Gabriele Campana Lucia Carboni Carmen Rossoni Santi Spampinato 《Biochimica et Biophysica Acta (BBA)/General Subjects》1994,1201(1):101-105
Addition of Zn2+_ to cell medium inhibited the induction of ornithine decarboxylase (ODC) activity in ODC overproducing L1210-DFMOr cells. A significant effect was observed at a concentration as low as 0.01 mM, however a more marked inhibition was caused by the addition of 0.1 mM Zn2+. The inhibition of the induction of ODC activity was accompanied by a proportional decrease in the content of immunoreactive ODC protein, whereas the level of ODC mRNA, detemined by a solution hybridization RNase protection assay, was not affected signigicantly. Instead, some acceleration of ODC turnover was observed. the addition of 0.1 mM Co2+ or Mn2+, but not of other divalent metal ions, also inhibited ODC induction; differently from Zn2+ however, these metals affected cell viability and/or cell growth. Removal of endogenous Zn2+ by a chelator also provoked a strong decrease of ODC induction, which was reversed by Zn2+. However, addition of Zn2+ in excess of the chelator proved to be markedly inhibitory. These results indicate that both a restricted Zn2+ availability and an enhanced presence of the metal can inhibit the induction of ODC in L1210-DFMOr cells. 相似文献
10.
Physiological responses of wheat genotypes grown in chelator-buffered nutrient solutions with increasing concentrations of excess HEDTA 总被引:1,自引:0,他引:1
The chelator-buffered nutrient solutions containing excess chelator have been used frequently in the micronutrient research,
but potential toxicity of the excess chelator has not been ascertained. The present study was conducted to test effects of
four concentrations of excess HEDTA [ N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid] and two levels of total Zn on growth,
root exudation, and nutrient uptake and transport by Triticum aestivum L. (cv. Aroona) and Triticum turgidum L. conv. durum
(Desf.) MacKey (cv. Durati) genotypes differing in tolerance to Zn deficiency. Excess HEDTA at 50 μM reduced root and shoot
growth and caused visual toxicity symptoms (necrotic lesions) on leaves; these effects were generally absent at lower concentrations
of excess HEDTA. Root exudation of phytosiderophores increased with increasing concentrations of excess HEDTA at deficient
and sufficient Zn levels, and was higher in Zn-deficiency-tolerant Aroona than in Zn-deficiency-sensitive Durati wheat. Shoot
and root Zn concentrations showed a saturable response to increasing Zn2+ activities in solution. Excess HEDTA at 50 μM caused an increase in shoot concentrations of Fe and a decrease in concentrations
of Mn and Cu. An average rate of Zn uptake increased with an increase in Zn2+ ionic activity in solution, with Zn-deficiency-tolerant Aroona having a higher rate of Zn uptake than Zn-deficiency-sensitive
Durati in the deficiency range of Zn2+ activities. Average uptake rates of Mn and Cu decreased with an increase in concentration of excess HEDTA. Similar observations
were noted for transport of Mn and Cu to shoots, while Zn transport to shoots was proportional to Zn2+ activities in solution. It was concluded that excess HEDTA at 50 μM adversely affects wheat growth and physiology, while
excess of 25 μM or less does not cause measurable toxicity.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
Summary 1. We examined the actions of mercury (Hg2+) and zinc (Zn2+) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg2+ and Zn2+. The threshold concentration for Hg2+ effects was 0.1 µM and that for Zn2+ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg2+ or 200µM Zn2+. The peak calcium current was reduced to 50% (IC50) by 1.1µM Hg2+ or 69µM Zn2+. While Zn2+ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg2+ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn2+ was not dependent on an open channel state, Hg2+ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg2+ and with higher concentrations (>100µM) of Zn2+.5. As Zn2+ in the concentration range used had no influence on resting membrane currents, Hg2+ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects. 相似文献
12.
The affinity of a number of bivalent and tervalent cations for the yeastCandida utilis was shown to decrease from Zn2+ to Ca2+. Ferric ions inhibited the uptake of Zn2+ but not vice versa. Inhibition of Zn2+ uptake in a synthetic medium with Fe3+ does not decrease the content of crude protein in cells. 相似文献
13.
The absorption characteristics of Cd2+ by 10- to 12-day-old soybean plants (Glycine max cv Williams) were investigated with respect to influence of Cd concentration on adsorption to root surfaces, root absorption, transport kinetics and interaction with the nutrient cations Cu2+, Fe2+, Mn2+, and Zn2+. The fraction of nonexchangeable Cd bound to roots remained relatively constant at 20 to 25% of the absorbed fraction at solution concentration of 0.0025 to 0.5 micromolar, and increased to 45% at solution concentration in excess of 0.5 micromolar. The exchangeable fraction represented 1.4 to 32% of the absorbed fraction, and was concentration dependent. Using dinitrophenol as a metabolic inhibitor, the `metabolically absorbed' fraction was shown to represent 75 to 80% of the absorbed fraction at concentration less than 0.5 micromolar, and decreased to 55% at 5 micromolar. At comparatively low Cd concentrations, 0.0025 to micromolar 0.3, root absorption exhibited two isotherms with K2 values of 0.08 and 1.2 micromolar. Root absorption and transfer from root to shoot of Cd2+ was inhibited by Cu2+, Fe2+, Mn2+, and Zn2+. Analyses of kinetic interaction of these nutrient cations with Cd2+ indicated that Cu2+, Fe2+, Zn2+, and possibly Mn2+ inhibited Cd absorption competitively suggesting an involvement of a common transport site or process. 相似文献
14.
Atsushi Takeda Haruna Tamano Wakana Hashimoto Shuhei Kobuchi Hiroki Suzuki Taku Murakami Munekazu Tempaku Yuta Koike Paul A. Adlard Ashley I. Bush 《Molecular neurobiology》2018,55(10):7775-7788
The role of metallothioneins (MTs) in cognitive decline associated with intracellular Zn2+ dysregulation remains unclear. Here, we report that hippocampal MT induction defends cognitive decline, which was induced by amyloid β1–42 (Aβ1–42)-mediated excess Zn2+ and functional Zn2+ deficiency. Excess increase in intracellular Zn2+, which was induced by local injection of Aβ1–42 into the dentate granule cell layer, attenuated in vivo perforant pathway LTP, while the attenuation was rescued by preinjection of MT inducers into the same region. Intraperitoneal injection of dexamethasone, which increased hippocampal MT proteins and blocked Aβ1–42-mediated Zn2+ uptake, but not Aβ1–42 uptake, into dentate granule cells, also rescued Aβ1–42-induced impairment of memory via attenuated LTP. The present study indicates that hippocampal MT induction blocks rapid excess increase in intracellular Zn2+ in dentate granule cells, which originates in Zn2+ released from Aβ1–42, followed by rescuing Aβ1–42-induced cognitive decline. Furthermore, LTP was vulnerable to Aβ1–42 in the aged dentate gyrus, consistent with enhanced Aβ1–42-mediated Zn2+ uptake into aged dentate granule cells, suggesting that Aβ1–42-induced cognitive decline, which is caused by excess intracellular Zn2+, can more frequently occur along with aging. On the other hand, attenuated LTP under functional Zn2+ deficiency in dentate granule cells was also rescued by MT induction. Hippocampal MT induction may rescue cognitive decline under lack of cellular transient changes in functional Zn2+ concentration, while its induction is an attractive defense strategy against Aβ1–42-induced cognitive decline. 相似文献
15.
G.M. Roomans A.P.R. Theuvenet Th.P.R. Van Den Berg G.W.F.H. Borst-Pauwels 《生物化学与生物物理学报:生物膜》1979,551(1):187-196
The uptake of Ca2+ and Sr2+ by the yeast Saccharomyces cerevisiae is energy dependent, and shows a deviation from simple Michaelis-Menten kinetics. A model is discussed that takes into account the effect of the surface potential and the membrane potential on uptake kinetics.The rate of Ca2+ and Sr2+ uptake is influenced by the cell pH and by the medium pH. The inhibition of uptake at low concentrations of Ca2+ and Sr2+ at low pH may be explained by a decrease of the surface potential.The inhibition of Ca2+ and Sr2+ uptake by monovalent cations is independent of the divalent cation concentration. The inhibition shows saturation kinetics, and the concentration of monovalent cation at which half-maximal inhibition is observed, is equal to the affinity constant of this ion for the monovalent cation transport system. The inhibition of divalent cation uptake by monovalent cations appears to be related to depolarization of the cell membrane.Phosphate exerts a dual effect on uptake of divalent cations: and initial inhibition and a secondary stimulation. The inhibition shows saturation kinetics, and the inhibition constant is equal to the affinity constant of phosphate for its transport mechanism. The secondary stimulation can only partly be explained by a decrease of the cell pH, suggesting interaction of intracellular phosphate, or a phosphorylated compound, with the translocation mechanism. 相似文献
16.
Pszon-Bartosz K Hansen JS Stibius KB Groth JS Emnéus J Geschke O Hélix-Nielsen C 《Biochemical and biophysical research communications》2011,414(1):96-100
The gene for a putative cation calcium exchanger (CCX) from Arabidopsis thaliana, AtCCX5, was cloned and its function was analyzed in yeast. Green fluorescent protein-tagged AtCCX5 expressed in yeast was localized in the plasma membrane and nuclear periphery. The yeast transformants expressing AtCCX5 were created and their growth in the presence of various cations (K+, Na+, Ca2+, Mg2+, Fe2+, Cu2+, Co2+, Cd2+, Mn2+, Ba2+, Ni2+, Zn2+, and Li+) were analyzed. AtCCX5 expression was found to affect the response to K+ and Na+ in yeast. The AtCCX5 transformant also showed a little better growth to Zn2+. The yeast mutant 9.3 expressing AtCCX5 restored growth of the mutant on medium with low K+ (0.5 mM), and also suppressed its Na+ sensitivity. Ion uptake experiments showed that AtCCX5 mediated relatively high-affinity K+ uptake and was also involved in Na+ transport in yeast. Taken together, these findings suggest that the AtCCX5 is a novel transport protein involves in mediating high-affinity K+ uptake and Na+ transport in yeast. 相似文献
17.
1. α-Mannosidase from jack-bean meal was purified 150-fold. β-N-Acetyl-glucosaminidase and β-galactosidase were removed from the preparation by treatment with pyridine. Zn2+ was added during the purification to stabilize the α-mannosidase. 2. At pH values below neutrality, α-mannosidase undergoes reversible spontaneous inactivation at a rate dependent on the temperature, the degree of dilution and the extent of purification. The enzyme is also subject to irreversible inactivation, which is prevented by the addition of albumin. 3. Reversible inactivation of α-mannosidase is accelerated by EDTA and reversed or prevented by Zn2+. Other cations, such as Co2+, Cd2+ and Cu2+, accelerate inactivation; an excess of Zn2+ again exerts a protective action, and so does EDTA in suitable concentration. 4. Neither Zn2+ nor EDTA has any marked effect in the assay of untreated enzyme. In an EDTA-treated preparation, however, Zn2+ reactivates the enzyme during assay. 5. It is postulated that α-mannosidase is a dissociable Zn2+–protein complex in which Zn2+ is essential for enzyme activity. 相似文献
18.
Chouduri AU Mishina K Shimizu T Yamazaki M Tokumoto T Yamada S 《Archives of biochemistry and biophysics》2008,477(1):113-120
The effect of Zn2+ on three major peptidase activities of the 20S proteasome purified from Xenopus oocytes was kinetically investigated. An extremely low concentration of Zn2+ (μM range) strongly inhibited the trypsin-like activity of the 20S proteasome which was fully recoverable by the addition of EDTA. The concentration of Zn2+ for half-maximum inhibition (K0.5) was 0.60 μM which was at least 10 times lower than that of any other divalent cation tested and essentially the same as for proteasomes purified from various other organisms indicating that the inhibition is highly Zn2+-specific, reversible, and common to the proteasome regardless of its source. Zn2+ at concentrations below 100 μM instantaneously activated the chymotrypsin-like and PGPH activities, and the Zn2+ concentration for half-maximum activation was found to be 42-48 μM. These activities were time-dependently inactivated by submillimolar concentrations of Zn2+. The inactivation rates were dependent on the concentration of Zn2+ and reached a maximum of 1.60-2.40 min−1 for the three peptidase activities under the conditions used. The Zn2+ concentration for half-maximum inactivation was found to be 0.70-1.23 mM. This time-dependent inactivation was not reversed by the addition of EDTA or DTT and might not be accompanied by the dissociation of subunits of the 20S proteasome indicating that all activities are inactivated by an identical phenomenon. These results reveal the three types of effects of Zn2+ on the 20S proteasome. 相似文献
19.
Vulkan R Yermiyahu U Mingelgrin U Rytwo G Kinraide TB 《The Journal of membrane biology》2004,202(2):97-104
Sorption of Cu2+ and Zn2+ to the plasma membrane (PM) of wheat root (Triticum aestivum Lcv. Scout 66) vesicles was measured at different pH values and in the presence of organic acids and other metals. The results were analyzed using a Gouy-Chapman-Stem model for competitive sorption (binding and electrostatic attraction) to a negative binding site. The binding constants for the two investigated cations as evaluated from the sorption experiments were 5 M–1 for Zn2+ and 400 M–1 for Cu2+. Thus, the sorption affinity of Cu2+ to the PM is considerably larger than that of Ca2+, Mg2+ or Zn2+. The greater binding affinity of Cu2+ was confirmed by experiments in which competition with La3+ for sorption sites was followed. The amount of sorbed Cu2+ decreased with increasing K+, Ca2+, or La3+ concentrations, suggesting that all these cations competed with Cu2+ for sorption at the PM binding sites, albeit with considerable differences among these cations in effectiveness as competitors with Cu2+. The sorption of Cu2+ and Zn2+ to the PM decreased in the presence of citric acid or malic acid. Citric acid (as well as pH) affected the sorption of Cu2+ or Zn2+ to PM more strongly then did malic acid. 相似文献
20.
Membrane potential-dependent calcium transport in right-side-out plasma membrane vesicles from Zea mays L. roots 总被引:7,自引:1,他引:6
Jacqueline Marshall Alfonso Corzo Roger A. Leigh Dale Sanders 《The Plant journal : for cell and molecular biology》1994,5(5):683-694
Right-side-out plasma membrane vesicles isolated from Zea mays roots were used to study membrane potential (ΔΨ)-dependent Ca2+ transport. Membrane potentials were imposed on the vesicles using either K+ concentration gradients and valinomycin or SCN concentration gradients, and the size of the imposed ΔΨ was measured with [14C]tetraphenylphosphonium. Uptake of 45Ca2+ into the vesicles was stimulated by inside-negative ΔΨ. The rate of transport increased to a maximum at a ΔΨ of about -80 mV and then declined at more negative ΔΨ. When extravesicular Ca2+ concentration was varied, uptake was maximal in the range 100–200 μM Ca2+. Neither dihydropyridine nor phenylalkylamine Ca2+ channel blockers had any effect on Ca2+ uptake but 30 μM ruthenium red was completely inhibitory with half maximal inhibition at 10–15 μM ruthenium red. Calcium transport was also inhibited by inorganic cations. Zn2+, Gd3+ and Mg2+ inhibited by a maximum of 30% while La3+, Nd3+ and Mn2+ inhibited by 70%. The inhibitory effects of La3+ and Gd3+ were additive. Lanthanum-insensitive Ca2+ five Ca2+ transport was totally inhibited by 80 μM Gd3+ and showed maximum activity at a ΔΨ of -60 mV, with less uptake at both higher and lower ΔΨ. Lanthanum and Gd3+ also inhibited Ca2+ uptake into protoplasts isolated from Zea roots and their individual and combined effects were similar in extent to those observed with plasma membrane vesicles. It is concluded that maize root plasma membrane contains two Ca2+-permeable channels that can be distinguished by their susceptibility to inhibition by La3+ and Gd3+. Both are inhibited by ruthenium red but not by other organic Ca2+ channel blockers. 相似文献