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1.
The calcium-dependent oxygen evolution activity of preparations of Phormidium luridum shows a marked selectivity in favor of ferricyanide over benzoquinone as Hill oxidant. In addition, the rate of oxygen evolution increases with increasing solution redox potential over the range +350 to +550 mV vs. the standard hydrogen electrode. These properties pertain to both 3-(3,4-dichlorophenyl)-1,1-dimethylurea-sensitive and -insensitive fractions of the total oxygen evolution activity. Neither changes in solution potential nor use of oxidants other than ferricyanide obviate the need for added Ca 2+. To explain these observations, two models are proposed, each of which invokes the existence of a redox component located within Photosystem II and having a midpoint potential greater than +450 mV. In one model, the postulated species is a donor which competes with water for oxidizing equivalents generated by System II. In the other model, the 450 mV species is a high-potential primary acceptor of System II electrons. 相似文献
2.
Calcium activation of oxygen evolution from French-press preparations of Phormidium luridum is largely reversible upon removal of added Ca(2+). Activation occurs via a first-order binding with a dissociation constant of 2.8 mM. An 8-fold increase in oxygen evolution rate observed upon Ca(2+) addition is accounted for by a 4-fold increase in the number of active photosynthetic units, and a doubling of turnover rate. While both Ca(2+) and Mg(2+) stimulate turnover, unit activation is Ca(2+) specific. Under optimal conditions, 30% of the units functioning in the intact cell can be recovered in the Ca(2+) -activated preparation. The Ca(2+) requirement of P. luridum preparations is not relieved by proton-carrying uncouplers, or by rate-saturating concentrations of the Hill acceptor, ferricyanide. Taken together with the reported stimulation by Ca(2+) of oxygen evolution in the presence of DCMU (Piccioni, R.G. and Mauzerall, D.C. (1976) Biochim. Biophys. Acta 423, 605--609) these observations strongly suggest a site of Ca(2+) action within Photosystem II. The pronounced specificity of the Ca(2+) requirement appears in preparations of other cyanobacteria (Anabaena flos-aquae and Anacystis nidulans) but not in the eucaryote Chlorella vulgaris. While milder cell-disruption methods bring about some Ca(2+) dependence in P. luridum, French-press treatment is required for maximal expression of Ca(2+) -specific effects. French-press breakage causes a release of endogenous Ca(2+) from cells, supporting the view that added Ca(2+) restores oxygen evolution by satisfying a physiological requirement for the cation. 相似文献
3.
Light-dependent Ca 2+ efflux via the Ca 2+/H + antiport in the photosynthetic purple sulfur bacterium Chromatium vinosum was inhibited by three phenothiazines: chlorpromazine; trifluoperazine and phenothiazine. The inhibitors had no effect on Ca 2+ uptake by C. vinosum in the dark nor any effect on the light-dependent efflux of either Na + or Tl + catalyzed, respectively, by the C. vinosum Na +/H + or K +/H + antiports. Ruthenium red and LaCl 3, neither of which inhibited light-dependent Ca 2+ efflux in C. vinosum, markedly inhibited Ca 2+ uptake in the dark by C. vinosum cells. Ruthenium red had no effect on the uptake of either Na +or the K + analog T1 + by C. vinosum cells in the dark. These results have been interpreted in terms of two separate Ca 2+ transport systems in C. vinosum: (i) a phenothiazine-sensitive and ruthenium red, La 3+-insensitive Ca 2+/H + antiport responsible for Ca 2+ efflux in the light; and (ii) a ruthenium red and La 3+-sensitive but phenothiazine-insensitive Ca 2+ uptake system. 相似文献
4.
Treatment of the oxygen-evolving photosystem II preparation from the thermophilic cyanobacterium Synechococcus sp. with EDTA inhibited electron flow from Z to P680 and consequently induced a back electron flow from Q −a to P680 +. The inhibition was reversed fully by Ca 2+and partially by Mn 2+ and Mg 2+ when EDTA-treated preparations had been incubated with respective divalent metal cations for several minutes, whereas diphenylcarbazide had no effect on the recombination between q −a and P680 + in EDTA-treated preparations. It is concluded that Ca 2+ is essential for electron transport from Z to P680. Oxygen evolution Electron transport Photosystem II Ca2+ Thermophilic cyanobacterium 相似文献
5.
Oxygen-evolving Photosystem II (PS II) particles were prepared from the thylakoid membranes of a chlorophyll b-less rice mutant, which totally lacks light-harvesting chlorophyll a/b proteins, after solubilization with β-octylglucoside. The preparation was essentially free of Photosystem I as judged from its low-temperature fluorescence spectrum and polypeptide composition. The PS II particles contained all the major subunit polypeptides of the PS II reaction center core complexes and the three extrinsic proteins related to oxygen evolution. The relative abundances of the 33, 21 and 15 kDa proteins were 100, 64 and 20%, respectively, of the corresponding proteins in the mutant thylakoids. The chlorophyll-to-Q A ratio was 53 and there was only one bound Ca 2+ per Q A. Thus, one of the two bound Ca 2+ present in the oxygen-evolving PS II membrane preparations from wild-type rice (Shen J.-R., Satoh, K. and Katoh, S. (1988) Biochim. Biophys. Acta 933, 358–364) is missing. The mutant PS II particles were highly active in oxygen evolution in the absence of exogenously added Ca 2+, although addition of 5 mM Ca 2+ enhanced the activity by 30%. When the 21 and 15 kDa proteins were supplemented to the particles, the Ca 2+-effect disappeared and the rate of oxygen evolution increased to a level exceeding 1000 μmol O 2 per mg chlorophyll per h. The results indicate that the number of Ca 2+ needed to promote a high rate of oxygen evolution is one per PS II in higher plants. 相似文献
6.
The effects of calcium ions (Ca 2+) on the stability of artichoke ( Cynara scolymus L.) peroxidase (AKPC) have been studied. The thermal stability of AKPC was improved by the addition of Ca 2+; the melting temperature increased by 20 °C and the deactivation energy by 26 kJ mol −1. AKPC was stable in a selection of organic solvents but was less active with 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) than under aqueous conditions. Ca 2+-free AKPC retained more activity in the presence of organic solvents due to its better maintenance of the rate of compound I formation with hydrogen peroxide (H 2O 2) compared to AKPC-Ca 2+. AKPC retained at least 75% activity over 24 h in the pH range 3.0–10.5 and about 50% over 1 month at pH 7.0 or 5.5, irrespective of the Ca 2+ content. AKPC-Ca 2+ was considerably more resistant to inactivation by H 2O 2 than Ca 2+-free AKPC suggesting that the presence of Ca 2+ boosts turnover under oxidizing conditions. AKPC has been applied as an alternative to horseradish peroxidase (HRP) in glucose concentration assays; the presence of Ca 2+ or of the Ca 2+ chelating agent ethylenediaminetetraacetic acid made no difference to the final result. The possibility is discussed that addition and removal of a labile Ca 2+ from AKPC could be used to control enzyme activity both in vivo and in vitro. 相似文献
7.
为了探明褪黑素(MT)和钙离子(Ca 2+)在调控植物耐热性中是否存在互作关系,以黄瓜幼苗为试材,分析了内源MT和Ca 2+对高温胁迫的响应;并通过叶面喷施100 μmol·L -1 MT、10 mmol·L -1 CaCl 2、3 mmol·L -1乙二醇二乙醚二胺四乙酸(EGTA,Ca 2+螯合剂)+100 μmol·L -1 MT、0.05 mmol·L -1氯丙嗪(钙调素拮抗剂,CPZ)+100 μmol·L -1 MT、100 μmol·L -1氯苯丙氨酸(p-CPA,MT合成抑制剂)+10 mmol·L -1 CaCl 2和去离子水(H 2O),研究高温下(42/32 ℃)外源MT和Ca 2+对黄瓜幼苗活性氧积累、抗氧化系统及热激转录因子( HSF)和热激蛋白( HSPs)等的影响。结果表明: 黄瓜幼苗内源MT和Ca 2+均受高温胁迫诱导;外源MT可上调常温下钙调素蛋白( CaM)、钙依赖蛋白激酶( CDPK5)、钙调磷酸酶B类蛋白( CBL3)、CBL结合蛋白激酶( CIPK2)mRNA表达;CaCl 2处理的MT合成关键基因色氨酸脱羧酶( TDC)、5-羟色胺-N-乙酰转移酶( SNAT)和N-乙酰-5-羟色胺甲基转移酶( ASMT)水平也显著升高,MT含量快速增加。MT和CaCl 2可显著增强高温下黄瓜的抗氧化能力,减少活性氧(ROS)积累,同时上调 HSF7、 HSP70.1和 HSP70.11 mRNA表达,从而减轻高温胁迫引起的过氧化伤害,植株热害症状明显减轻,热害指数和电解质渗漏率显著降低。加入EGTA和CPZ后,MT对黄瓜幼苗抗氧化能力和热激蛋白表达的促进效应明显减弱,Ca 2+对高温下黄瓜幼苗过氧化伤害的缓解效应也被p-CPA逆转。可见,MT和Ca 2+均可诱导黄瓜幼苗的耐热性,二者在热胁迫信号转导过程中存在互作关系。 相似文献
8.
The intracellular free Ca 2+ ion concentration ([Ca 2+]i) was measured using fura-2 microspec-trofluorimetry in individual rat pancreatic β-cells prepared by enzymatic digestion and fluorescence-activated cell sorting. The mean basal concentration of [Ca 2+]i in β-cells in the presence of 4.4 mM glucose and 1.8 mM Ca 2+ was 112±1.6 nM (n=207). The action of acetylcholine (ACh) was concentration-dependent, and raising the concentration resulted in [Ca 2+]i spikes of increasing amplitude and duration in some, but not all of the β-cells. In addition, the β-cells demonstrated variable sensitivity to ACh. The increases in [Ca 2+]i were rapid, transient and were blocked by atropine at 10 -6M. A brief exposure to 50 mM K + resulted in a transient increase in [Ca 2+]i similar to that induced by ACh, but resistant to atropine. A high concentration of ACh (100μL 10 -4M or 10 -3M) induced [Ca 2+]i oscillations in 11 out of 57 β-cells in the presence of 4.4 mM glucose. Using calcium channel blockers and Ca 2+ free medium, the source of the increase in [Ca 2+]i was deduced to be from extracellular spaces. Changing the temperature from 22 to 37°C did not affect the action of ACh on [Ca 2+]i. These data strongly suggest that ACh exerted a direct action on [Ca 2+]i in normal rat pancreatic β-cells and support a role for Ca 2+ as a second messenger in the action of ACh. 相似文献
9.
A cell-free preparation has been isolated from Phormidium luridum that evolves oxygen when coupled to one-electron oxidants, that is insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and that yields oxygen at a rate dependent on redox potential. In this preparation the Hill oxidant couples closer to the oxygen-producing apparatus than in any other cell-free system. Light saturation curve data for the cell-free preparation shows a stabilization, by the Hill oxidant, of intermediates in oxygen synthesis. In whole cells coupled to CO 2 or to K 3 Fe(CN) 6 no such stabilization occurs and a 2nd order light intensity dependence of the oxygen-production rate is observed. 相似文献
10.
The kinetics of fluorescence yield in Chlorella pyrenoidosa and spinach chloroplasts were studied in the time range of 0.5 μs to several hundreds of microseconds in the presence of hydroxylamine. Fluorescence was excited with a just-saturating xenon flash with a halfwidth of 13 μs (λ = 420 nm). The fast rise of the fluorescence yield which was limited by the rate of light influx, was, in the presence of 10 −3–10 −2 M hydroxylamine, replaced by a slow component which had a half risetime of 25 μs in essence independent of light intensity. This slow fluorescence yield increase reflects a dark reaction on the watersplitting side of Photosystem II. Simultaneous oxygen evolution measurements suggested that a fast fluorescence component is only present in organisms with intact O 2-evolving system, whereas a slow rise predominantly occurs in organisms with the watersplitting system irreversibly inhibited by hydroxylamine. The results can be explained by the following hypotheses: (a) The primary donor of Photosystem II in its oxidized state, P+, is a fluorescence quencher. (b) Hydroxylamine prevents the secondary electron donor Z from reducing the oxidized reaction center pigment P+ rapidly. This inhibition is dependent on hydroxylamine concentration and is complete at a concentration of 10−2 M. (c) A second donor (not transporting electrons from water) transfers electrons to P+ with a half time of roughly 25 μs. 相似文献
11.
The roles of Ca 2+ and Cl − on the photosynthetic O 2 yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl − deficiency on the O 2 yield and on the S-state distribution was analyzed. As the results show, omission of both Ca 2+ and Cl − (Mn 2+ present) almost totally inhibited O 2 evolution. When Ca 2+ was replaced by Na +, a substantial reduction of the O 2 yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl − was displaced by NO −3, which is equivalent to Cl − deficiency of the water-splitting complex, a substantial reduction of the O 2 yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO −3 containing samples with those in control samples indicated that Cl − deficiency allowed accumulation of oxidizing equivalents up to the S 3 state but modified the final step of O 2 evolution. Moreover, those centers which advanced to the S 3 state in the absence of Cl − deactivated in a special way which involved a faster deactivation of S 2 and an increased formation of S −1. 相似文献
12.
The role of Ca 2+ in glycerol dissimilation under hypoosmotic stress in the halotolerant alga Dunaliella tertiolecta was investigated using a pharmacological approach. A stretch-activated Ca 2+ channel blocker, GdCl 3, inhibited glycerol dissimilation under hypoosmotic stress. However, addition of voltage-dependent Ca 2+ channel blockers and inhibitors of mitochondrial and endoplasmic reticulum Ca 2+ channels did not affect the glycerol dissimilation under hypoosmotic stress. The results of the present study suggest that the influx of Ca 2+ from the extracellular space via the stretch-activated Ca 2+ channels localized in the plasma membrane is required for the transduction of osmotic signal of D. tertiolecta. 相似文献
13.
The properties of the membrane-bound ATPase (EC 3.6.1.3) of Escherichia coli have been reexamined using membranes obtained by mechanical disruption of exponentially growing cells. The activity exhibited an absolute requirement for Mg2+ in the neutral pH range, while Ca2+ was found able to activate ATPase at more alkaline pH. Optimal activity was observed at pH 7.5, with a Mg/ATP ratio of 0.5. ADP was found to inhibit ATP hydrolysis and to transform the Michaelian ATP concentration dependence with a Km of 0.5 mM into a sigmoid curve with increasing Km and decreasing V. In contrast ADP activated an ATP-ADP exchange process and this shift from hydrolysis to exchange was stimulated by high Mg2+ and by orthophosphate. All nucleoside triphosphates tested interfered with ATP hydrolysis, all could be hydrolyzed and could donate their terminal phosphate group to ADP. The relative efficiencies of nucleoside triphosphates in these three processes varied in parallel with minor discrepancies. ATP hydrolysis was inhibited by N,N′-dicyclohexylcarbodiimide (DCCD) Dio 9, NaN3 and pyrophosphate, the first two being ineffective against ATP-ADP exchange, the third being stimulatory and the last inhibitory. ATP hydrolysis and ATP-ADP exchange are tentatively attributed to the terminal enzyme of oxidative phosphorylation. 相似文献
14.
To quantitatively understand intracellular Na + and Cl − homeostasis as well as roles of Na +/K + pump and cystic fibrosis transmembrane conductance regulator Cl − channel ( ICFTR) during the β1-adrenergic stimulation in cardiac myocyte, we constructed a computer model of β1-adrenergic signaling and implemented it into an excitation-contraction coupling model of the guinea-pig ventricular cell, which can reproduce membrane excitation, intracellular ion changes (Na +, K +, Ca 2+ and Cl −), contraction, cell volume, and oxidative phosphorylation. An application of isoproterenol to the model cell resulted in the shortening of action potential duration (APD) after a transient prolongation, the increases in both Ca 2+ transient and cell shortening, and the decreases in both Cl − concentration and cell volume. These results are consistent with experimental data. Increasing the density of ICFTR shortened APD and augmented the peak amplitudes of the L-type Ca 2+ current ( ICaL) and the Ca 2+ transient during the β1-adrenergic stimulation. This indirect inotropic effect was elucidated by the increase in the driving force of ICaL via a decrease in plateau potential. Our model reproduced the experimental data demonstrating the decrease in intracellular Na + during the β-adrenergic stimulation at 0 or 0.5 Hz electrical stimulation. The decrease is attributable to the increase in Na + affinity of Na +/K + pump by protein kinase A. However it was predicted that Na + increases at higher beating rate because of larger Na + influx through forward Na +/Ca 2+ exchange. It was demonstrated that dynamic changes in Na + and Cl − fluxes remarkably affect the inotropic action of isoproterenol in the ventricular myocytes. 相似文献
15.
Influence of oxygen on the electron transfers of photosynthesis. II. Influence of very low oxygen concentration on the NADP+ reduction by isolated chloroplastsThe influence of very low O2 concentration on the NADP+ reduction by isolated spinach chloroplasts has been studied. The results show that in the presence of very low O2 concentration (< 0.3%) NADP+ reduction is partially inhibited. This inhibition may be partially reversed under some conditions, especially when, in spite of the presence of an O2 trap (glucose plus glucose oxidase (EC 1.1.3.4)) an O2 evolution is observed. 相似文献
16.
Control of leaf and head rot of Chinese cabbage ( Brassica campestris L. ssp. pekinensis), caused by Pythium tracheiphilum, was obtained by Clonostachys rosea (isolate IK726) in field trials conducted in 1995 and 1999 on naturally infested land in a commercial crop in Denmark. A significant 2-3-fold disease reduction was obtained at an application rate of 10 8-10 9 conidia m -2 (high application rate) in both years, but not at a 10-fold reduced rate in 1999. Disease reduction by Trichoderma harzianum (Supresivit) was almost significant at the high application rate (1 g product m -2 corresponding to 7×10 9 colony forming units (CFUs) m -2) in both years, but not at a 10-fold reduced rate applied in 1999. In both 1995 and 1999 trials, the percentage of marketable heads increased significantly by 10% following a full application rate of C. rosea. Supresivit applied at the full application rate gave a significant 13% yield improvement in 1995 but not in 1999. No yield improvement was found when the two agents were applied at 10-fold reduced rates. A Danish T. harzianum isolate significantly increased yield by 13% in 1995, but gave no disease control. Plant growth promotion may have been responsible for yield improvements obtained by Supresivit and the Danish isolate of T. harzianum. The 1995 trial also evaluated the products Binab T ( T. harzianum+ T. polysporum), Mycostop ( Streptomyces griseoviridis), Polyversum ( P. oligandrum) and Aliette (fosetyl-Al) and Danish isolates of P. oligandrum (2) and T. virens (1), none of which gave disease control or yield effects. 相似文献
17.
高Ca 2+环境对许多植物的生长不利, 因此研究植物对高Ca 2+环境的适应机制非常重要。研究发现, 拟南芥( Ara- bidopsis thaliana)镁转运体MGT7功能缺失突变体 mgt7-1和 mgt7-2具有高Ca 2+敏感表型: 在高Ca 2+培养基上, 相对于野生型Col-0, 突变体叶鲜重显著下降, 但根长无显著差异。高Ca 2+对 MGT7启动子活性和包括 MGT7在内的镁转运体基因表达无显著调节作用。Col-0与 mgt7突变体之间, 在外加Ca 2+诱导细胞质Ca 2+瞬时升高和Ca 2+含量方面无显著差异; 但是, 在正常和高Ca 2+培养基上, mgt7突变体的Mg含量均显著低于Col-0。高Ca 2+显著抑制Col-0和 mgt7突变体内Mg的积累。因此我们假设, mgt7突变体的高Ca 2+敏感表型是由于其体内Mg含量下降导致的。进一步的研究证实, 只有增加培养基中Mg 2+的含量, 而不是N、P、K和S, 才可以使突变体的高Ca 2+敏感表型得到恢复。 相似文献
18.
The adjustment of Ca 2+ entry in cardiac cells is critical to the generation of the force necessary for the myocardium to meet the physiological needs of the body. In this review, we present the concept that Ca 2+ can promote its own entry through Ca 2+ channels by different mechanisms. We refer to it under the general term of ‘Ca2+-induced Ca2+ entry’ (CICE). We review short-term mechanisms (usually termed facilitation) that involve a stimulating effect of Ca 2+ on the L-type Ca 2+ current ( ICa-L) amplitude (positive staircase) or a lessening of Ca 2+-dependent inactivation of ICa-L. This latter effect is related to the amount of Ca 2+ released by ryanodine receptors (RyR2) of the sarcoplasmic reticulum (SR). Both effects are involved in the control of action potential (AP) duration. We also describe a long-term mechanism based on Ca 2+-dependent down-regulation of the Kv4.2 gene controlling functional expression of the repolarizing transient outward K + current ( Ito) and, thereby, AP duration. This mechanism, which might occur very early during the onset of hypertrophy, enhances Ca 2+ entry by maintaining Ca 2+ channel activation during prolonged AP. Both Ca 2+-dependent facilitation and Ca 2+-dependent down-regulation of Ito expression favour AP prolongation and, thereby, promote sustained voltage-gated Ca 2+ entry used to enhance excitation–contraction (EC) coupling (with no change in the density of Ca 2+ channels per se). These self-maintaining mechanisms of Ca 2+ entry have significant functions in remodelling Ca 2+ signalling during the cardiac AP. They might support a prominent role of Ca 2+ channels in the establishment and progression of abnormal Ca 2+ signalling during cardiac hypertrophy and congestive heart failure. 相似文献
19.
The formation and the organization of Photosystem II photosynthetic units during the greening of a dark-grown Chlorella vulgaris, mutant 5/520, have been investigated by analysing the kinetics of the “activation” of oxygen evolution and of the fluorescence induction. 1. 1. The existence during the early stages of the greening of a stationary photosynthesis demonstrates the presence of active Photosystem II at these initial stages, which are integrated in a functional whole, leading to overall photosynthesis. 2. 2. The rise-time of oxygen evolution has been measured using far-red and green light in order to estimate the relative number of chlorophylls per unit. The amount of chlorophyll a remains relatively constant during the greening, while the progressive addition of chlorophyll b causes the size of the units to increase approx. 2-fold. 3. 3. The induction kinetics of the fluorescence are exponential during the early phases of greening and later become distinctly sigmoidal; this suggests that the first units synthesized on the surface of the membrane are isolated from each other by obstacles preventing electronic excitation transfers and that such obstacles which might correspond to some distance between such units, can disappear at later stages, allowing energy transfers to occur.
These observations suggest that the Photosystem II units represent organized functional entities. They apparently consist of a relatively constant number of chlorophyll a molecules, which during the greening is complemented progressively by the addition of chlorophyll b. 相似文献
20.
为探讨大黄鱼幼鱼在低氧及酸化胁迫下机体离子调节情况,本研究探讨了低氧(溶解氧量DO 3.5 mg·L-1,pH 8.1)、酸化(DO 7.0 mg·L-1,pH 7.35)以及低氧酸化协同胁迫(DO3.5 mg·L-1,pH 7.35)对大黄鱼幼鱼鳃组织结构以及离子调节相关生理指标的影响.结果 表明:低氧胁迫下,大黄鱼... 相似文献
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