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1.
The effects of barium, strontium and magnesium upon lens permeability characteristics were studied in the presence and absence of 2 mM calcium in the bathing medium. Permeability characteristics were determined by measuring lens potential, resistance and 42K efflux rates. Barium and strontium at equimolar concentrations to calcium were able to substitute for calcium in controlling lens sodium permeability. Magnesium was ineffective in this respect.Small changes in resistance and 42K efflux rates occurred when calcium was eliminated from bathing solution containing either 2 mM barium or strontium. These changes were interpreted to be the result of an increase in lens permeability to potassium. When 2 mM strontium was added to calcium-containing solution, there was no significant change in the electrical or flux parameters of the lens. However, the addition of 2 mM barium to calcium-containing solution resulted in a 54% increase in lens resistance and a 13 mV depolarization. These observations indicated a barium-induced decrease in lens permeability to potassium, and this was confirmed by an observed decrease in 42K efflux rate constant under similar experimental conditions.The rapid time course of all the observed changes implies that they are the result of changes in the permeability characteristics of membranes lying close to the surface of the lens. 相似文献
2.
Calmodulin-depleted isotonic erythrocyte ghosts contain 200 ng residual calmodulin/mg protein which is not removed by extensive washings at pCa2+ > 7. Specific activity and Ca2+-affinity of the (Ca2+ + Mg2+)ATPase increase at increasing calmodulin, with K0.5 Ca of 0.38 μM at calmodulin concentrations corresponding to that in erythrocytes. High Ca2+ concentrations inhibit the enzyme. Specific activity and Ca2+-affinity of the enzyme decrease at increasing Mg2+ concentrations. The Ca2+ ? Mg2+ antagonism is likewise observed at inhibitory Ca2+ concentrations. 相似文献
3.
Abstract Cell envelopes of Pseudomonas fluorescens , cytoplasmic membrane, peptidoglycan and outer membrane were obtained from a fractionation procedure and tested for their metal binding capacity. Isolated envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) were chemically modified and functional carboxyl groups transformed to electropositive amine groups, using carbodiimide ethylenediamine. Transformation of carboxyl groups was evaluated by measuring total amine groups in all fractions (modified or not). Using equilibrium dialysis and Scatchard plots for the data, we have established that isolated unmodified cell envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) possess at least two types of metal binding sites with different association constants ( K a and K 'a ). Introduction of positive charges into the bacterial envelopes resulted in the disappearance of one type of metal binding site which had the highest association constant value for Ni2+ , Cu2+ and Zn2+ . All fractions, modified or not, always presented at least two types of binding sites with different association constants for Cd2+ . 相似文献
4.
5.
The classical E2-P intermediate of (Na+ + K+)-ATPase dephosphorylates readily in the presence of K+ and is not affected by the addition of ADP. To determine the significane in the reaction cycle of (Na+ + K+)-ATPase of kinetically atypical phosphorylations of rat brain (Na+ + K+)-ATPase we compared these phosphorylated components with the classical E2-P intermediate of this enzyme by gel electrophoresis. When rat brain (Na+ + K+)-ATPase was phosphorylated in the presence of high concentrations of Na+ a proportion of the phosphorylated material formed was sensitive to ADP but resistant to K+. Similarly, if phosphorylation was carried out in the presence of Na+ and Ca2+ up to 300 pmol/mg protein of a K+-resistant, ADP-sensitive material were formed. If phosphorylation was from [γ-32P]CTP up to 800 pmol 32P/mg protein of an ADP-resistant, K+-sensitive phosphorylated matterial were formed. On gel electrophoresis these phosphorylated materials co-migrated with authentic Na+-stimulated, K+-sensitive, E2-P-phosphorylated intermediate of (Na+ + K+)-ATPase, supporting suggestions that they represent phosphorylated intermediates in the reaction sequence of this enzyme. 相似文献
6.
Ca2+ inhibited the Mg2+-dependent and K+-stimulated p-nitrophenylphosphatase activity of a highly purified preparation of dog kidney (Na+ + K+)-ATPase. In the absence of K+, however, a Mg2+-dependent and Ca2+-stimulated phosphatase was observed, the maximal velocity of which, at pH 7.2, was about 20% of that of the K+-stimulated phosphatase. The Ca2+-stimulated phosphatase, like the K+-stimulated activity, was inhibited by either ouabain or Na+ or ATP. Ouabain sensitivity was decreased with increase in Ca2+, but the K0.5 values of the inhibitory effects of Na+ and ATP were independent of Ca2+ concentration. Optimal pH was 7.0 for Ca2+-stimulated activity, and 7.8–8.2 for the K+-stimulated activity. The ratio of the two activities was the same in several enzyme preparations in different states of purity. The data indicate that (a) Ca2+-stimulated phosphatase is catalyzed by (Na+ + K+)-ATPase; (b) there is a site of Ca2+ action different from the site at which Ca2+ inhibits in competition with Mg2+; and (c) Ca2+ stimulation can not be explained easily by the action of Ca2+ at either the Na+ site or the K+ site. 相似文献
7.
Specific activity and Ca2+-affinity of (Ca2++Mg2+)ATPase of calmodulin-depleted ghosts progressively increase during preincubation with 0.1–2 mM Ca2+. Concomitantly, the increment in ATPase activity caused by calmodulin and the binding of calmodulin to ghosts decrease. The effects of calcium ions are abolished by the addition of calmodulin. ATP protects the enzyme from a Ca2+-dependent decrease of the maximum activity but does not seem to influence the Ca2+-dependent transformation of the low Ca2+-affinity enzyme into a high Ca2+-affinity form. 相似文献
8.
Joseph D. Robinson 《生物化学与生物物理学报:生物膜》1983,727(1):63-69
Na+-ATPase activity of a dog kidney (Na+ + K+)-ATPase enzyme preparation was inhibited by a high concentration of NaCl (100 mM) in the presence of 30 μM ATP and 50 μM MgCl2, but stimulated by 100 mM NaCl in the presence of 30 μM ATP and 3 mM MgCl2. The for the effect of MgCl2 was near 0.5 mM. Treatment of the enzyme with the organic mercurial thimerosal had little effect on Na+-ATPase activity with 10 mM NaCl but lessened inhibition by 100 mM NaCl in the presence of 50 μM MgCl2. Similar thimerosal treatment reduced (Na+ + K+)-ATPase activity by half but did not appreciably affect the for activation by either Na+ or K+, although it reduced inhibition by high Na+ concentrations. These data are interpreted in terms of two classes of extracellularly-available low-affinity sites for Na+: Na+-discharge sites at which Na+-binding can drive E2-P back to E1-P, thereby inhibiting Na+-ATPase activity, and sites activating E2-P hydrolysis and thereby stimulating Na+-ATPase activity, corresponding to the K+-acceptance sites. Since these two classes of sites cannot be identical, the data favor co-existing Na+-discharge and K+-acceptance sites. Mg2+ may stimulate Na+-ATPase activity by favoring E2-P over E1-P, through occupying intracellular sites distinct from the phosphorylation site or Na+-acceptance sites, perhaps at a coexisting low-affinity substrate site. Among other effects, thimerosal treatment appears to stimulate the Na+-ATPase reaction and lessen Na+-inhibition of the (Na+ + K+)-ATPase reaction by increasing the efficacy of Na+ in activating E2-P hydrolysis. 相似文献
9.
采用砂培法,研究了匍茎翦股颖对Cu2+、Zn2+、Cd2+与Pb2+胁迫的生长响应及阈限浓度,结果表明:种子萌发率随着4种重金属浓度的增加而下降。对株高的影响是当重金属浓度小于100mg/L时会促进株高生长,高于100mg/L则产生抑制作用。Cu2+显著抑制根系生长,并随浓度的增加抑制效应愈加显著;在Cu2+浓度为600mg/L时匍茎翦股颖的根长比对照下降了93.75%。Cu2+、Zn2+、Pb2+浓度小于200mg/L时会促进地上生物量的增加,但高于200mg/L时,地上生物量会随着3种重金属的增加而减少。Cu2+、Zn2+浓度小于100mg/L或Cd2+、Pb2+浓度小于200mg/L会增加叶绿素的含量,高浓度会降低叶绿素的含量;Cd2+在浓度为600mg/L时显著降低叶绿素含量,与对照相比,下降了43.55%。匍茎翦股颖生长的综合效应分析表明,匍茎翦股颖对Cu2+胁迫最敏感,具有较低的阈限浓度,而Zn2+胁迫对匍茎翦股颖的生长影响最小,阈限浓度相对较高。 相似文献
10.
R.J. Bradley W.O. Romine M.M. Long T. Ohnishi M.A. Jacobs D.W. Urry 《Archives of biochemistry and biophysics》1977,178(2):468-474
Based on a proposed solution conformation of the Ca2+ ion complex of the repeat hexapeptide of elastin, l-Val-l-Ala-l-Pro-Gly-l-Val-Gly, it is possible to modify the molecule making it more lipophilic for lipid bilayer permeation while retaining its complexation features. Therefore the two peptides, For-MeVal-Ala-Pro-Sar-Pro-Sar-OMe and For-MeVal-Ala-Pro-Sar-Pro-Sar-OH, were synthesized and evaluated for lipid bilayer activity and cation binding (For, N-formyl; Me, N-methyl; Sar, N-methyl glycine). Both peptides bound Ca2+ preferentially but did not exhibit the properties of a Ca2+ carrier. They were however active as K+ carriers although K+ ion titration curves showed a much lower affinity for K+ than for Ca2+. The addition of Ca2+ or Mg2+ to the bilayer system inhibited the peptide K+ carrier activity. Three possible explanations of this interesting Ca2+ inhibition of carrier activity are irreversible complexation of Ca2+, mixed ligand complex formation involving Ca2+, lipid and peptide, and impermeability of the lipid layer when peptide is complexed with a divalent cation. 相似文献
11.
Vesicles isolated from rat heart, particularly enriched in sarcolemma markers, were examined for their sidedness by investigation of side-specific interactions of modulators with the asymmetric (Na+ + K+)-ATPase and adenylate cyclase complex. The membrane preparation with the properties expected for inside-out vesicles showed the highest rate of ATP-driven Ca2+ transport. The Ca2+ pump was stimulated 1.7- and 2.1-fold by external Na+ and K+, respectively, the half-maximal activation occurring at 35 mM monovalent cation concentration. In vesicles loaded with Ca2+ by pump action in a medium containing 160 mM KCl, a slow spontaneous release of Ca2+ started after 2 min. The rate of this release could be dramatically increased by the addition of 40 mM NaCl to the external medium. In contrast, 40 mM KCl exerted no appreciable effect on vesicles loaded with Ca2+ in a medium containing 160 mM NaCl. Ca2+ movements were also studied in the absence of ATP and Mg2+. Vesicles containing an outwardly directed Na+ gradient showed the highest Ca2+ uptake activity. These findings suggested the operation of a Ca2+/Na+ antiporter in addition to the active Ca2+ pump in these sarcolemmal vesicles. A valinomycin-induced inward K+-diffusion potential stimulated the Na+- Ca2+ exchange, suggesting its electrogenic nature. If in the absence of ATP and Mg2+ the transmembrane Nai+/Nao+ gradient exceeded 160/15 mM concentrations, Ca2+ uptake could be stimulated by the addition of 5 mM oxalate, indicating Na+ gradient-induced Ca2+ uptake to be a translocation of Ca2+ to the lumen of the vesicle. A sarcoplasmic reticulum contamination, removed by further sucrose gradient fractionation, contained rather low Na+-Ca2+ exchange activity. This result suggests that the activity can be entirely accounted for by the sarcolemmal content of the cardiac membrane preparation. 相似文献
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13.
In this paper previous binding studies of Mg2+ and Mn2+ ions to tRNA's are reconsidered. Binding data of some re- presentative examples are interpreted including interactions between charges located on the macroion. Both curved and bell-shaped Scatchard plots can be accounted for quantitatively if corrections are made for electrostatic interactions and, if necessary, for the effect of conformational changes on these interactions. It appears that there is no need to invoke more than one class of binding sites on tRNA's, meaning that the experimental binding data can be described using the same in- trinsic pK value for all phosphate groups. 相似文献
14.
J.T. OFlaherty S. Cousart C.L. Swendsen L.R. DeChatelet D.A. Bass S.H. Love C.E. McCall 《生物化学与生物物理学报:生物膜》1981,640(1):223-230
The influence of extracellular Ca2+ and Mg2+ on the transport of 2-deoxy-[3H]glucose into human polymorphonuclear neutrophils was studied. Omission of these cations from the cell suspensions had little effect on resting hexose uptake. Furthermore, the addition of the bivalent cation chelator, EDTA, depressed uptake only slightly. Similarly, neither cation was essential for the enhanced 2-deoxy-D-[3H]glucose uptake stimulated by two chemotactic factors (C5a and ) and arachidonic acid: enhanced uptake was only partially depressed by the omission of Ca2+ and Mg2+ from the suspensions and was still prominent in the presence of EDTA. Two other neutrophil stimulants, the ionophores, A23187 and ionomycin, also enhanced hexose uptake but their actions were heavily dependent upon extracellular bivalent cations and were totally abrogated by EDTA. In all instances, extracellular Ca2+, but not Mg2+, supported optimal enhanced hexose transport induced by stimuli.Activation of 2-deoxy-D-[3H]glucose uptake by each of the five stimuli was totally blocked by cytochalasin B (a blocker of carrier-mediated hexose transport) and D-glucose but not by L-glucose. The data indicate, therefore, that a variety of neutrophil stimulants activate carrier-mediated hexose transport. Although this transport can be triggered by the movement of extracellular Ca2+ into the cell (as exemplified by the action of the two ionophores), such Ca2+ movement is not required for the actions of chemotactic factors or arachidonic acid. Other mechanisms, such as a rearrangement of intracellular Ca2+, may be involved in mediating the activation of hexose transport induced by the latter stimuli. 相似文献
15.
Paul Jensén 《Physiologia plantarum》1982,56(3):259-265
Effects of interrupted K+ supply on different parameters of growth and mineral cation nutrition were evaluated for spring wheat (Triticum aestivum L. cv. Svenno). K+ (2.0 mM) was supplied to the plants during different periods in an otherwise complete nutrient solution. Shoot growth was reduced before root growth after interruption in K+ supply. Root structure was greatly affected by the length of the period in K+ -free nutrient solution. Root length was minimal, and root branching was maximal within a narrow range of K+ status of the roots. This range corresponded to cultivation for the last 1 to 3 days, of 11 in total, in K+ -free nutrient solution, or to continuous cultivation in solution containing 0.5 to 2 mM K+. In comparison, both higher and lower internal/external K+ concentrations had inhibitory effects on root branching. However, the differing root morphology probably had no significant influence on the magnitude of Ca2+, Mg2+ and Na+ uptake. Uptake of Ca2+ and especially Mg2+ significantly increased after K+ interruption, while Na+ uptake was constant in the roots and slowly increased in the shoots. The two divalent cations could replace K+ in the cells and maintain electroneutrality down to a certain minimal range of K+ concentrations. This range was significantly higher in the shoot [110 to 140 μmol (g fresh weight)?1] than in the root [20 to 30 μmol (g fresh weight)?1]. It is suggested that the critical K+ values are a measure of the minimal amount of K+ that must be present for physiological activity in the cells. At the critical levels, K+ (86Rb) influx and Ca2+ and Mg2+ concentrations were maximal. Below the critical K+ values, growth was reduced, and Ca2+ and Mg2+ could no longer substitute for K+ for electrostatic balance. In a short-term experiment, the ability of Ca2+ to compete with K+ in maintaining electroneutrality in the cells was studied in wheat seedlings with different K+ status. The results indicate that K+, which was taken up actively and fastest at the external K+ concentration used (2.0 mM), partly determines the size of Ca2+ influx. 相似文献
16.
N.Charle Morcos 《生物化学与生物物理学报:生物膜》1982,688(3):747-756
N-Ethylmaleimide was employed as a surface label for sarcolemmal proteins after demonstrating that it does not penetrate to the intracellular space at concentrations below 1·10?4 M. The sarcolemmal markers, ouabain-sensitive (Na+ + K+)-ATPase and Na+/Ca2+-exchange activities, were inhibited in N-ethylmaleimide perfused hearts. Intracellular activities such as creatine phosphokinase, glutamate-oxaloacetate transaminase and the internal phosphatase site of the Na+ pump (K+-p-nitrophosphatase) were not affected. Almost 20% of the (Ca2+ + Mg2+)-ATPase and Ca2+ pump were inhibited indicating the localization of a portion of this activity in the sarcolemma. Sarcolemma purified by a recent method (Morcos, N.C. and Drummond, G.I. (1980) Biochim. Biophys. Acta 598, 27–39) from N-ethylmaleimide-perfused hearts showed loss of approx. 85% of its (Ca2+ + Mg2+-ATPase and Ca2+ pump compared to control hearts. (Ca2+ + Mg2+)-ATPase and Ca2+ pump activities showed two classes of sensitivity to vanadate ion inhibition. The high vanadate affinity class ( for inhibition approx. 1.5 μM) may be localized in the sarcolemma and represented approx. 20% of the total inhibitable activity in agreement with estimates from N-ethylmaleimide studies. Sucrose density fractionation indicated that only a small portion of Mg2+-ATPase and Ca2+-ATPase may be associated with the sarcolemma. The major portion of these activities seems to be associated with high density particles. 相似文献
17.
Inge-Bert Täljedal 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,372(1):154-161
The fluorescence of microdissected pancreatic islets of ob/ob-mice was studied by microscope photometry after incubation with 10 μM chlorotetracycline. In Krebs-Ringer bicarbonate buffer, excitation at 390 nm yielded peak emission at 530 nm, suggesting that chelated Ca2+ was the major source of fluorescence. In support of this interpretation, incubation in Ca2+-free buffer markedly decreased the fluorescence, whereas withdrawal of Mg2+ increased it. Raising the Mg2+ concentration to 15 mM suppressed the fluorescence. In the presence of Ca2+, the substitution of choline ions for Na+ increased the fluorescence considerably; in the absence of Ca2+, however, Na+ deficiency had only little effect. Control experiments showed that Na+ or choline ions had no effect on the fluorescence of Ca2+-chlorotetracycline in 70 or 90% methanol. In 90%, but not in 70%, methanol 15 mM Mg2+ slightly quenched the fluorescence from 2.5 mM Ca2+ and 10 μM chlorotetracycline. It is suggested that Na+, and perhaps Mg2+, tends to decrease the amount of membrane-bound Ca2+ in the pancreatic islets. 相似文献
18.
Yingmei Zhang Yejing Wang Runliu Yu Sheng Zhang Zhenbin Wu 《Frontiers of Biology in China》2008,3(1):50-54
The effects of heavy metals Cd2+, Pb2+ and Zn2+ at 0.05, 0.5 and 5.0 mg/L level and their interactions at 0.5 mg/L level on DNA damage in hepatopancreas of loach Misgurnus anguillicaudatus for 1–35 days exposure were examined by single cell gel electrophoresis (SCGE). For each test group, 20 loaches with similar
body size (5.17–7.99 g; 11.79–13.21 cm) were selected and kept in aquaria with dechlorinated water at (22±1)°C and fed a commercial
diet every 48 h. According to the percentage of damaged DNA with tail and its TL/D (tail length to diameter of nucleus) value,
the relationship between DNA damage degree and heavy metal dose and exposure time was determined. Results showed that the
percentage of damaged DNA and the TL/D value were increased with the prolonged exposure time. The highest percentage (84.85%)
of damaged DNA was shown in 5.0 mg/L Zn2+ group after 28 days exposure and the biggest TL/D value (2.50) in all treated groups after 35 days exposure. During the first
treated week, the damnification of DNA was mainly recognized as the first level, after that time, the third damaged level
was mostly observed and the percentage of damaged DNA was beyond 80%. The joint toxic effects among Cd2+, Pb2+ or Zn2+ revealed much complexity, but it generally displayed that the presence of Cd2+ could enhance the genotoxicity of Pb2+ or Zn2+. In conclusion, the results suggested that there was a significant time-and dose-depended relationship between the heavy
metal and DNA damage in hepatopancreas of loach, and SCGE could represent a useful means to evaluate the genotoxicity of environmental
contamination on aquatic organisms.
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Translated from Acta Hydrobiologica Sinica, 2006, 30(4): 399–403 [译自: 水生生物学报] 相似文献
19.
Entry of the divalent cations Ni2+ , Co2+ and Zn2+ into cells of maize ( Zea mays L. cv. Dekalb XL 85) root tissue is accompanied by an acidification of the incubation medium, a decrease in both the pH of the cell sap and the level of malate in the cells, and by an inhibition of dark fixation of CO2 . K+ , on the contrary, induces only a very low acidification of the incubation medium, does not change either the pH of the cell sap or the malate level in the cells, and induces an increase in CO2 dark fixation. Different mechanisms are postulated for the stimulation of proton extrusion by divalent cations and K+ . 相似文献
20.
Levels of Mg2+, Ca2+ and Fe2+/Fe3+ were determined in roots and shoots of sugar beet seedlings (Beta vulgaris L. cv. Monohill) cultured for 5 weeks in a complete nutrient solution to which either Cd2+ (0, 5 or 50 μM), EDTA (0, 10 or 100 μM) or a combination of both was added. The plants subjected to the various treatments showed a variety of deficiency symptoms. Leaves of the Cd2+-treated plants became thin and chlorotic (Mg- and Fe-deficiency symptoms). The plants showed reduced growth and developed only a few brownish roots with short laterals (Ca-deficiency symptoms). EDTA treatment resulted in green, stunted, hard leaves and reduced growth (Ca-deficiency symptoms). The deficiency symptoms observed correspond well with the observed uptake rates and distributions of Mg2+, Ca2+ and Fe2+/Fe3+. Increases in either Cd2+, EDTA or a combination of both in the growth medium, were correlated with increasing Mg2+ levels in the roots and with decreasing Mg2+ levels in the shoots. Cd2+ alone or in combination with EDTA had little influence on Ca2+ levels in the shoots but decreased Ca2+ levels in the roots. Thus, Cd2+ affects Mg2+ and Ca2+ transport in opposite ways: Mg2+ transport to the shoots is inhibited while that of Ca2+ is facilitated. Treatment with EDTA alone did not affect Ca2+ concentrations in either the shoots or the roots. Treatment with Cd2+ lowered Fe2+ concentrations in both roots and shoots. 相似文献