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1.
Thylakoids and Photosystem II particles prepared from the cyanobacterium Synechococcus PCC 7942 washed with a HEPES/glycerol buffer exhibited low rates of light-induced oxygen evolution. Addition of either Ca2+ or Mg2+ to both thylakoids and Photosystem II particles increased oxygen evolution independently, maximal rates being obtained by addition of both ions. If either preparation was washed with NaCl, light induced O2 evolution was completely inhibited, but re-activated in the same manner by Ca2+ and Mg2+ but to a lower level. In the presence of Mg2+, the reactivation of O2 evolution by Ca2+ allowed sigmoid kinetics, implying co-operative binding. The results are interpreted as indicating that not only Ca2+, but also Mg2+, is essential for light-induced oxygen evolution in thylakoids and Photosystem II particles from Synechococcus PC 7942. The significance of the reactivation kinetics is discussed. Reactivation by Ca2+ was inhibited by antibodies to mammalian calmodulin, indicating that the binding site in Photosystem II may be analogous to that of this protein.Abbreviation HEPES n-2-Hydroxyethylpiperazine--2-ethane sulphonic acid  相似文献   

2.
Tobacco plants (Nicotiana tabacum L. cv. Sevilla) were grown under controlled conditions. The leaf content of Ca2+, Mg2+ and K+, and the activity of the pyruvate kinase were analyzed. The increased application of Ca2+ diminished the content of K+ and Mg2+ in leaves, and decreased the activity of pyruvate kinase. Taking into account these results, we suggest the pyruvate kinase activity as an bioindicator of the contents of the Ca2+, Mg2+ and K+.  相似文献   

3.
Rhizobium tropici, R. leguminosarum bv phaseoli and R. loti each have an active C4-dicarboxylic acid transport system dependent on an energized membrane. Free thiol groups are probably involved at the active site. Since EDTA inhibited succinate transport in R. leguminosarum bv phaseoli and R. loti, divalent cations may participate in the process; the activity was reconstituted by the addition of Ca2+ or Mg2+. However, EDTA had no effect on succinate transport in R. tropici, R. meliloti or R. trifolii strains. Ca2+ or Mg2+ had a similar effect on the growth rates of R. tropici and R. leguminosarum bv phaseoli; R. tropici did not require Ca2+ to grow on minimal medium supplemented with succinate but R. leguminosarum bv phaseoli required either or both of the divalent cations Ca2+ and Mg2+. A R. tropici Mu-dI (lacZ) mutant defective in dicarboxylic acid transport, was isolated and found unable to form effective bean nodules.The authors are with the Division of Biochemistry, Instituto de Investigaciones Biológicas Clemente Estable, Avda, Italia 3318, 11.600 Montevideo, Uruguay  相似文献   

4.
Eccentric is a newly-isolated mutant of Paramecium tetraurelia that fails to swim backwards in response to Mg2+. In the wild type, this backward swimming results from Mg2+ influx via a Mg2+-specific ion conductance (I Mg. Voltage-clamp analysis confirmed that, as suspected, step changes in membrane potential over a physiological range fail to elicit I Mg from eccentric. Further electrophysiological investigation revealed a number of additional ion-current defects in eccentric: (i) The Ca2+ current activated upon depolarization inactivates more slowly in eccentric than in the wild type, and it requires longer to recover from this inactivation. (ii) The Ca2+-dependent Na+ current deactivates significantly faster in the mutant, (iii) The two K+ currents observed upon hyperpolarization are reduced by >60% in eccentric. It is difficult to envision how these varied pleiotropic effects could result from loss of a single ion current. Rather, they suggest that the eccentric mutation affects a global regulatory system. Two plausible hypotheses are discussed.We are grateful to Dr. Yoshiro Saimi for his comments and suggestions on this work, and for the support of the Lucille P. Markey Charitable trust and the National Institutes of Health (GM22714 and GM38646).  相似文献   

5.
为探明大果沙枣树体矿质离子渗透调节机制,比较分析了盐渍化生境中1~12a生树的根、枝和叶部主要矿质阳离子的吸收、分配特征.结果 表明:(1)大果沙枣树体内Ca2+的积累量最高(13.79 g/kg),K+次之(5.92 g/kg),Na+最低(1.00 g/kg);随着树龄的增大,大果沙枣根部的Na+以及枝和叶部的K+...  相似文献   

6.
The Mg2+-dependency of Ca2+-induced ATP hydrolysis is studied in basolateral plasma membrane vesicles from rat kidney cortex in the presence of CDTA and EGTA as Mg2+- and Ca2+-buffering ligands. ATP hydrolysis is strongly stimulated by Mg2+ with a Km of 13 μ M in the absence or presence of 1 μ M free Ca2+. At free Mg2+ concentrations of 1 μ M and lower, ATP hydrolysis is Mg2+ -independent, but is strongly stimulated by submicromolar Ca2+ concentrations Km = 0.25 μM, Vmax = 24 μmol Pi/h per mg protein). The Ca2+-stimulated ATP hydrolysis strongly decreases at higher Mg2+ concentrations. The Ca2+-stimulated Mg2+-independent ATP hydrolysis is not affected by calmodulin or trifluoperazine and shows no specificity for ATP over ADP, ITP and GTP. In contrast, at high Mg2+ concentrations calmodulin and trifluoperazine affect the high affinity Ca2+-ATPase activity significantly and ATP is the preferred substrate. Control studies on ATP-dependent Ca2+-pumping in renal basolaterals and on Ca2+-ATPase in erythrocyte ghosts suggest that the Ca2+-pumping enzyme requires Mg2+. In contrast, a role of the Ca2+-stimulated Mg2+-independent ATP hydrolysis in active Ca2+ transport across basolateral membranes is rather unlikely.  相似文献   

7.
以1年生西伯利亚白刺水培幼苗为材料,研究了不同浓度NaCl(0、200、400mmol·L~(-1))处理对幼苗生长及不同器官(根、茎、叶)中Na~+、K~+、Ca~(2+)、Mg~(2+)的吸收、运输与分配的影响,探讨西伯利亚白刺的盐适应机制。结果表明:(1)200mmol·L~(-1) NaCl处理促进了西伯利亚白刺幼苗的生长及叶片肉质化程度,400mmol·L-1 NaCl处理显著抑制其生长。(2)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根、茎、叶中Na~+含量显著增加,且叶中Na~+含量显著高于茎和根中;根系中K~+含量显著增加;根、茎、叶中Ca~(2+)、Mg~(2+)含量在200mmol·L~(-1) NaCl处理下保持平稳或上升,而在400mmol·L-1 NaCl处理下显著下降。(3)各器官中K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+比值总体随NaCl处理浓度的升高呈下降趋势,且根部离子比值始终高于叶片和茎。(4)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根-茎SK,Na显著下降,而根-茎SCa,Na、SMg,Na及茎-叶SK,Na、SCa,Na、SMg,Na逐渐提高。研究发现,西伯利亚白刺的盐适应机制主要是通过植株的补偿生长效应及叶片对Na~+的聚积作用实现的,同时也与根系对K~+的扣留及茎叶对K~+、Ca~(2+)、Mg~(2+)选择性运输能力增强有关。  相似文献   

8.
Dipicolinic acid synthesis inPenicillium citreoviride strain 3114 was inhibited by Ca2+ ions, but not by Ba2+, Cu2+or Fe2+. Among the metals tested, only Zn2+ inhibited the synthesis of dipicolinic acid and promoted sporulation. None of these metals reversed the inhibition by Ca2+ or Zn2+. A mutant 27133-dpa-ca selected for resistance to feedback inhibition by dipicolinic acid: Ca2+ complex showed cross-resistance to inhibition by dipicolinic acid: Zn2+. Both 3114 and271 33-dpa-ca excreted a number of aliphatic and amino acids during secondary metabolism of dipicolinic acid. In the presence of 1000 ppm of Ca2+, accumulation of citric acid and α-aminoadipic acid was completely inhibited under conditions of inhibition of dipicolinic acid in parent strain 3114 but not in the mutant. Citric acid with or without Ca2+ did not inhibit thede novo synthesis of dipicolinic acid in the strain 3114. In fact, citric acid in the presence of Ca2+ improved significantly rate of dipicolinic acid synthesis. Apart from resistance to feed back inhibition by dipicolinic acid: Ca2+ complex, mutant differed from the parent in three other aspectsviz. (i) dipicolinic acid synthesis was not subject to catabolite repression by glucose, (ii) sporulation as well as dipicolinic acid synthesis was dependent on the presence of Ca2+ ions in the medium and (iii) Mg2+ requirement for the mutant increased three fold. Higher requirement of the Mg2+ could be partially relieved by Ca2+ during secondary metabolism. The results support the inference thatde novo synthesis of dipicolinic acid is regulated through feedback inhibition by dipicolinic acid: Ca2+complex.  相似文献   

9.
Summary The purified 20,000-dalton fragment of sarcoplasmic reticulum (Ca2++Mg2+)-ATPase has been shown by us (A.E. Shamoo, T.E. Ryan, P.S. Stewart, D.H. MacLennan, 1976. J. Biol. Chem.251:4147) to have Ca2+-selective ionophoric activity. The Ca2+-ionophoric fragment has been purified by either SDS-column chromatography or SDS-preparative gel electrophoresis. The Ca2+-ionophoric fragment has been subjected to prolonged dialysis to insure the removal of bound SDS from the fragment. The selectivity sequence of this fragment in black lipid membranes (BLM) formed from either oxidized cholesterol or phosphatidylcholine/cholesterol is the same,P Ba>P Ca>P Sr>P Mg>P Mn. This selectivity sequence is the same as that for the intact (Ca2+ +Mg2+)-ATPase. Treatment of the fragment with cholate to absolutely insure the removal of bound SDS resulted in the fragment having a selectivity sequence as above except thatP Mn>P Mg. This and other data indicate that the 20,000-dalton fragment is the site containing the Ca2+-ionophoric activity of the (Ca2++Mg2+)-ATPase.  相似文献   

10.
Paracoccus denitrificans grown on complex medium deficient in Mg2+ and Ca2+ are rendered lysozyme susceptible by washing with NaCl, whereas cells grown in a succinate-salts medium (Mg2+ and Ca2+ sufficient) or complex medium supplemented with Mg2++Ca2+ are not. The material released by water washing of cells grown on complex medium and complex medium supplemented with Mg2+ and Ca2+ was characterized by a high protein content. There was a high lipid: protein ratio and an appreciable amount of 3-deoxyoctulosonic acid in the material released by NaCl washing of cells grown under all conditions, indicating release of outer membrane material. The lipid ornithine: lipid phosphorous ratios of NaCl wash from cells grown on complex medium and complex medium supplemented with Mg2+ and Ca2+ were 0.54 and 0.34, respectively. Although NaCl washing removed outer membrane material from cells grown under all conditions, only divalent cation deficient cells were rendered lysozyme susceptible. This might be explained by the increased outer membrane ornithine-containing lipid to phospholipid ratio in these cells yielding a more permeable outer membrane.  相似文献   

11.
The phospholipid requirement of the (Ca2+ + Mg2+)-ATPase present in a membrane fraction from human platelets was studied using various purified phospholipases. Only those phospholipases, which hydrolyse the negatively charged phospholipids, inhibited the (Ca2+ + Mg2+)-ATPase activity. The ATPase activity could be restored by adding mixed micelles of Triton X-100 and phosphatidylserine or phosphatidylinositol. Micelles with phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine or sphingomyelin could not be used for reconstitution and inhibited the activity of the native enzyme.  相似文献   

12.
Summary Removal of Ca2+ from the medium results in depolarization of theChara internodal cell and an increase in membrane conductance (G m). The increase in conductance is associated with an increase in K+ conductance, as judged by Ca2+ effects on the K+ dependence of clamp current. The voltage dependence ofG m is also affected by Ca2+, as is the time course of the response of clamp current to a step change in voltage. Mg2+ restores the low conductance and the fast response to a voltage change, but not hyperpolarization at neutral pH, suggesting that there is an additional, independent effect on the electrogenic pump. The membrane does not show the normal ability to increase proton conductance at high pH in the absence of Ca2+; this is also restored by Mg2+ as well as by Ca2+.  相似文献   

13.
The intracellular Ca2+ content of nontransformed Balb/c3T3 cells is two to three times higher than that of a spontaneously transformed derivative. Depriving either cell type of extracellular Mg2+ causes a 2- to 3-fold increase in their Ca2+ content over a 24-hr period. Restoring Mg2+ to the medium decreases the Ca2+ content of the cells to their original values in about the same time. The increase in Ca2+ content is not blocked by cycloheximide suggesting that normal rates of protein synthesis are not required to produce this effect. Mg2+ deprivation also decreases the initial rate of Ca2+ efflux from the transformed cells and increases the size of the slowly exchanging fraction of Ca2+ to the levels found in the nontransformed cells. Since Mg2+ deprivation normalizes the appearance and growth behavior of the transformed cells, the possible intermediary role of Ca2+ in this normalization was studied. Large changes in extracellular Ca2+ produced large changes in the Ca2+ content of the transformed cells with little change in appearance or thymidine incorporation rate. Ca2+ deprivation did inhibit thymidine incorporation in early passage nontransformed cells; however with repeated passage, this effect decreased, as did the Ca2+ content of these cells. The possible role of Mg2+ in regulating cellular Ca2+ content and distribution is discussed, as is the relation of Ca2+ content and distribution to the development of the transformed state.  相似文献   

14.
The gating of ryanodine receptor calcium release channels (RyRs) depends on myoplasmic Ca2+ and Mg2+ concentrations. RyRs from skeletal and cardiac muscle are activated by μm Ca2+ and inhibited by mm Ca2+ and Mg2+. 45Ca2+ release from skeletal SR vesicles suggests two mechanisms for Mg2+-inhibition (Meissner, Darling & Eveleth, 1986, Biochemistry 25:236–244). The present study investigates the nature of these mechanisms using measurements of single-channel activity from cardiac- and skeletal RyRs incorporated into planar lipid bilayers. Our measurements of Mg2+- and Ca2+-dependent gating kinetics confirm that there are two mechanisms for Mg2+ inhibition (Type I and II inhibition) in skeletal and cardiac RyRs. The mechanisms operate concurrently, are independent and are associated with different parts of the channel protein. Mg2+ reduces P o by competing with Ca2+ for the activation site (Type-I) or binding to more than one, and probably two low affinity inhibition sites which do not discriminate between Ca2+ and Mg2+ (Type-II). The relative contributions of the two inhibition mechanisms to the total Mg2+ effect depend on cytoplasmic [Ca2+] in such a way that Mg2+ inhibition has the properties of Types-I and II inhibition at low and high [Ca2+] respectively. Both mechanisms are equally important when [Ca2+] = 10 μm in cardiac RyRs or 1 μm in skeletal RyRs. We show that Type-I inhibition is not the sole mechanism responsible for Mg2+ inhibition, as is often assumed, and we discuss the physiological implications of this finding. Received: 1 January 1996/Revised: 14 November 1996  相似文献   

15.
Cardiac plasma membrane Ca2+/Mg2+ ecto-ATPase (myoglein) requires millimolar concentrations of either Ca2+ or Mg2+ for maximal activity. In this paper, we report its localization by employing an antiserum raised against the purified rat cardiac Ca2+/Mg2+ ATPase. As assessed by Western blot analysis, the antiserum and the purified immunoglobulin were specific for Ca2+/Mg2+ ecto-ATPase; no cross reaction was observed towards other membrane bound enzymes such as cardiac sarcoplasmic reticulum Ca2+-pump ATPase or sarcolemmal Ca2+-pump ATPase. On the other hand, the cardiac Ca2+/Mg2+ ecto-ATPase was not recognized by antibodies specific for either cardiac sarcoplasmic reticulum Ca2+-pump ATPase or plasma membrane Ca2+-pump ATPase. Furthermore, the immune serum inhibited the Ca2+/Mg2+ ecto-ATPase activity of the purified enzyme preparation. Immunofluorescence of cardiac tissue sections and neonatal cultured cardiomyocytes with the Ca2+/Mg2+ ecto-ATPase antibodies indicated the localization of Ca2+/Mg2+ ecto-ATPase in association with the plasma membrane of myocytes, in areas of cell-matrix or cell-cell contact. Staining for the Ca2+/Mg2+ ecto-ATPase was not cardiac specific since the antibodies detected the presence of membrane proteins in sections from skeletal muscle, brain, liver and kidney. The results indicate that Ca2+/Mg2+ ecto-ATPase is localized to the plasma membranes of cardiomyocytes as well as other tissues such as brain, liver, kidney and skeletal muscle.  相似文献   

16.
Forty bacterial isolates from the effluents of a gelatin factory (Jabalpur, India) were screened for protease activity and the two most potent producers were identified as Bacillus laterosporus and a Flavobacterium sp. The enzymes of both isolates were optimal at pH 8 and 60°C, with maximum activity after 90 min. The enzyme activity of B. laterosporus was suppressed by Fe2+, Mg2+, Mn2+ and Zn2+ ions but was enhanced by Ba2+ and Ca2+. That of Flavobacterium sp. was suppressed by Mg2+ and Mn2+ ions but enhanced by Ba2+, Ca2+ and Fe2+. The enzyme activity of the former was strongly inhibited by KCN, whereas that of the latter was only slightly inhibited by 8-hydroxyquinoline.  相似文献   

17.
Magnesium-limited chemostat cultures of Klebsiella pneumoniae NCTC 418 with 20 M CaCl2 in the medium showed a low rate of gluconate plus 2-ketogluconate production relative to potassium- or phosphate-limited cultures. However, when the medium concentration of CaCl2 was increased to 1 mM, the glucose dehydrogenase (GDH) activities also increased and became similar to those observed in potassium- or phosphate limited cultures. It is concluded that this is due to Mg2+ and Ca2+ ions being involved in the binding of pyrroloquinoline quinone (PQQ) to the GDH apoenzyme. There seems to be an absolute requirement of divalent cations for proper enzyme functioning and in this respect Ca2+ ions could replace Mg2+ ions. The high GDH activity which has been found in cells grown under Mg2–-limited conditions in the presence of higher concentrations of Ca2+ ions, is compatible with the earlier proposal that GDH functions as an auxiliary energy generating system involved in the maintenance of high transmembrane ion gradients.Abbreviations PQQ pyrroloquinoline quinone - GDH glucose dehydrogenase (EC 1.1.99.17) - GaDH gluconate dehydrogenase (EC 1.1.99.3) - CAP chloramphenicol - WB Wurster's Blue [1,4-bis-(dimethylamino)-benzene perchlorate]  相似文献   

18.
The Paramecium cell membrane was voltage-clamped under K current suppression conditions. Ciliary beating was registered using high-speed video microscopy. Depolarizing step pulses activated a transient inward current and induced reversed ciliary beating. Very strong positive steps inhibited ciliary reversal during the pulse suggesting inhibition of the Ca influx. We call the potential, which is sufficiently positive to induce transition from reversed to normal ciliary beating, the transition potential. The transition potential rose with increasing external Ca2+ showing saturation beyond 1 mM Ca2+. Addition of Mg2+, Ba2+ or K+ to the 1 mM Ca2+ bathing solution depressed the transition potential in a concentration-dependent manner. The depolarization-activated inward Ca current increased with rising external Ca concentration, and addition of either Mg2+, Ba2+ or K2+ diminished the inward Ca current. The diverging results of Ca2+-dependent positive shifts, and Mg2+-(Ba2+-, K+-) dependent negative shifts in transition potential are compared with shifts of VImax. It is concluded that external cations bind competitively — in addition to membrane surface charges — to affinity sites of Ca channel, where they specifically modulate permeation of calcium.  相似文献   

19.
Werner M. Kaiser  Steve Huber 《Planta》1994,193(3):358-364
Nitrate reductase in spinach (Spinacia oleracea L.) leaves was rapidly inactivated in the dark and reactivated by light, whereas in pea (Pisum sativum L.), roots, hyperoxic conditions caused inactivation, and anoxia caused reactivation. Reactivation in vivo, both in leaves and roots, was prohibited by high concentrations (10–30 M) of the serine/threonine-protein phosphatase inhibitors okadaic acid or calyculin, consistent with the notion that protein dephosphorylation catalyzed by type-1 or type-2A phosphatases was the mechanism for the reactivation of NADH-nitrate reductase (NR). Following inactivation of leaf NR in vivo, spontaneous reactivation in vitro (in desalted extracts) was slow, but was drastically accelerated by removal of Mg2+ with excess ethylenediaminetetraacetic acid (EDTA), or by desalting in a buffer devoid of Mg2+. Subsequent addition of either Mg2+, Mn2+ or Ca2+ inhibited the activation of NR in vitro. Reactivation of NR (at pH 7.5) in vitro in the presence of Mg2+ was also accelerated by millimolar concentrations of AMP or other nucleoside monophosphates. The EDTA-mediated reactivation in desalted crude extracts was completely prevented by protein-phosphatase inhibitors whereas the AMP-mediated reaction was largely unaffected by these toxins. The Mg2+-response profile of the AMP-accelerated reactivation suggested that okadaic acid, calyculin and microcystin-LR were rather ineffective inhibitors in the presence of divalent cations. However, with partially purified enzyme preparations (5–15% polyethyleneglycol fraction) the AMPmediated reactivation was also inhibited (65–80%) by microcystin-LR. Thus, the dephosphorylation (activation) of NR in vitro is inhibited by divalent cations, and protein phosphatases of the PP1 or PP2A type are involved in both the EDTA and AMP-stimulated reactions. Evidence was also obtained that divalent cations may regulate NR-protein phosphatase activity in vivo. When spinach leaf slices were incubated in Mg2+ -and Ca2+-free buffer solutions in the dark, extracted NR was inactive. After addition of the Ca2+ /Mg2+-ionophore A 23187 plus EDTA to the leaf slices, NR was activated in the dark. It was again inactivated upon addition of divalent cations (Mg2+ or Ca2+). It is tentatively suggested that Mg2+ fulfills several roles in the regulatory system of NR: it is required for active NR-protein kinase, it inactivates the protein phosphatase and is, at the same time, necessary to keep phospho-NR in the inactive state. The EDTA- and AMP-mediated reactivation of NR in vitro had different pH optima, suggesting that two different protein phosphatases may be involved. At pH 6.5, the activation of NR was relatively slow and the addition or removal of Mg2+ had no effect. However, 5-AMP was a potent activator of the reaction with an apparent K m of 0.5 mM. There was also considerable specificity for 5AMP relative to 3- or 2-AMP or other nucleoside monophoposphates. We conclude that, depending upon conditions, the signals triggering NR modulation in vivo could be either metabolic (e.g. 5-AMP) or physical (e.g. cytosolic [Mg2+]) in nature.Abbreviations DTT dithiothreitol - Mops 3-(N-morpholino)propanesulfonic acid - NR NADH-nitrate reductase - NRA nitrate-reductase activity - PP protein phosphatase This paper is dedicated to Prof. O.K. Volk on the occasion of his 90th birthdayThe skilled technical assistance of Elke Brendle-Behnisch is gratefully acknowledged. The investigations were cooperatively supported by the Deutsche Forschungsgemeinschaft (SFB 251), the U.S. Department of Agriculture, Agricultural Research Services, Raleigh, NC. This work was also supported in part by a grant from the U.S. Department of Energy (Grant DE-A I05-91 ER 20031 to S.C.H.).  相似文献   

20.
Grapevine (Vitis vinifera cv. Monastrell) cell suspension cultures were treated with 1.5 mM fosetyl-Al, a frequently used systemic fungicide for grapevine diseases caused by oomycetes. These cells showed a reduction in the level of peroxidase activity secreted into the culture media when compared to non-treated cells, the effect being mainly related to a decrease in the level of the basic B1 peroxidase isozyme. The effect of fosetyl-Al on peroxidase was analogous to that observed with the Ca2+-channel blockers Co2+, Cd2+ and La3+, and was counteracted by Ca2+ ions, but was not reversed when the Ca2+-ionophore A23187 was added to the culture media. Moreover, the effect of fosetyl-Al on peroxidase activity and peroxidase isozymes was also partially reversed by Mg2+ ions but not by Sr2+, and was accentuated by Ba2+ ions. These results suggested that Ca2+ and Mg2+ ions specifically overcome the inhibitory effect of fosetyl-Al on peroxidase. In this context, an apoplastic Ca2+/Mg2+-displacement hypothesis is proposed for the mechanism of action of fosetyl-Al on peroxidase from grapevine cells.  相似文献   

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