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1.
The Y-organs of crustaceans secrete ecdysteroids (molting hormones)and are regulated (negatively) by a neurosecretory peptide,molt-inhibiting hormone (MIH). Signaling path(s) in Y-organswere explored that connect MIH receptors ultimately with suppressionof receptor number for the uptake of cholesterol (ecdysteroidprecursor) and of gene expression of steroidogenic enzymes.Experiments were conducted in vitro with Y-organs of crabs (Cancerantennarius, Menippe mercenaria) and crayfishes (Orconectessp.). It was confirmed in all species that steroidogenesis occursin the absence of external calcium (Ca++), but increases toa maximum as Ca++ is increased to 1 to 10 mM and is substantiallyinhibited at higher Ca++ concentrations. MIH does not requireexternal Ca++ for inhibitory action, but inhibition is eliminatedby high Ca++concentrations. Several experimental approachesfailed to find evidence of phospholipase C activation, turnoverof inositol triphosphate or diacylglycerol generation connectedwith steroidogenesis. Unbinding or chelation of intracellularCa++ with thapsigargin or TMB-8, respectively both caused dose-dependentinhibition of ecdysteroid output. Blockade of Ca++ channelswith verapamil, nifedipine or nicardipine also inhibited steroidogenesis;highest doses inhibited profoundly to below Ca++-free basallevels. Inhibition also was obtained with all doses of the Ca++channel agonist/antagonist (–) BAY K 8644 in crabs, butin crayfishes lower doses were stimulatory. However, if thecrayfish cells were depolarized, allowing greater Ca++ influx,the previously stimulatory doses of BAY K 8644 became inhibitory.Y-organ protein kinase C (PKC) is Ca++-sensitive. Activationof PKC was uniformly stimulatory in crabs, but inhibitory incrayfishes. Cytochalasin D, which disrupts the actin cytoskeleton,and which causes moderate Ca++ influx, stimulated hormone formation.These results are interpreted to indicate a regulatory rolefor Ca++ in ecdysteroidogenesis, involving a local, submembranecirculation of Ca++ through ion channels and Ca++ pumps andinteraction with PKC in phosphorylating key proteins. An optimallocal Ca++ environment fostering hormone synthesis is evidentsince too little or too much Ca++ is inhibitory. Methyl farnesoate (MF) had no effect on ecdysone productionin crab or crayfish Y-organs in 24-hr incubations with MF at100 pM to 10 µM.  相似文献   

2.
MERTZ  DAN 《Plant & cell physiology》1970,11(2):273-279
Cultures of Gibberella fujikuroi grown under continuous illuminationof 1800 lux incorporated over 60% more leucine into the gibberellinsthan dark controls. In the dark at a C/N ratio of 37.6 Ca++increased the incorporations of leucine into A3 to essentiallythe same level as the light-stimulated incorporation. The failureof Ca++ to increase gibberellin synthesis in the dark at a C/Nratio of 9.4 suggested that light and Ca++ were exerting theirregulatory roles at different sites. (Received October 15, 1969; )  相似文献   

3.
The mechanism involved inN-methyl-D-glucamine(NMDA)-induced Ca2+-dependentintracellular acidosis is not clear. In this study, we investigated indetail several possible mechanisms using cultured rat cerebellargranule cells and microfluorometry [fura 2-AM or 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-AM].When 100 µM NMDA or 40 mM KCl was added, a marked increase in theintracellular Ca2+ concentration([Ca2+]i)and a decrease in the intracellular pH were seen. Acidosis wascompletely prevented by the use ofCa2+-free medium or1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, suggesting that it resulted from an influx of extracellular Ca2+. The following fourmechanisms that could conceivably have been involved were excluded:1)Ca2+ displacement of intracellularH+ from common binding sites;2) activation of an acid loader or inhibition of acid extruders; 3)overproduction of CO2 or lactate; and 4) collapse of the mitochondrialmembrane potential due to Ca2+uptake, resulting in inhibition of cytosolicH+ uptake. However,NMDA/KCl-induced acidosis was largely prevented by glycolyticinhibitors (iodoacetate or deoxyglucose in glucose-free medium) or byinhibitors of the Ca2+-ATPase(i.e.,Ca2+/H+exchanger), including La3+,orthovanadate, eosin B, or an extracellular pH of 8.5. Our results therefore suggest that Ca2+-ATPaseis involved in NMDA-induced intracellular acidosis in granule cells. Wealso provide new evidence that NMDA-evoked intracellular acidosisprobably serves as a negative feedback signal, probably with theacidification itself inhibiting the NMDA-induced[Ca2+]i increase.

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4.
The triangular exchanges Cu++–Zn++–Ca++ have beenperformed in the Nitella flexilis cell wall. The selectivitysequence for the exchange of the cations is Cu++ » Zn++> Ca++. The presence of two types of exchange site has beenconfirmed. Possibly due to the Jahn-Teller effect, the cupricion forms inner-sphere coordination with functional groups ofthe sites. This results in lower rotional mobilities and loweractivity coefficients of the curpric ions immobilized closeto the negative charges in the Stern layer. At higher equivalentfractions, the cupric ions in the diffuse layer are more mobileand have activity coefficients close to one.  相似文献   

5.
Phaseolus moves its leaves upward and downward with circadianperiod. This movement of the leaf results from the differentialchange in the turgor on opposite sides of the pulvinus. Concentrations of K+, Na+, Mg++, and Ca++ in the upper and lowerhalves of the pulvinus and the water content of cells on bothsides of it were analyzed in relation to the deformation ofthe pulvinus. The results showed that (1) the pulvinus was deformedby expansion and contraction of the cells on its opposite sides;(2) among the four cations, the K+ concentration was markedlyhigh in both halves of the pulvinus; (3) the osmotic pressureof the upper and lower halves were nearly equal during the rhythmicdeformation of the pulvinus; (4) the expansion and contractionof the cells on the opposite sides of the pulvinus have a positivecorrelation only with a change in the K+ concentration expressedin terms of µmoles per mg protein; (5) the concentrationsof other cations such as Na+, Mg++, Ca++, expressed in termsof µmoles per mg protein, did not change during the circadiandeformation of the pulvinus. Thus, the rhythmic K+ movementseems to be the basis for pulvinar turgor movements. With respectto the mechanism of K+ movement, three possibilities are discussed. (Received November 7, 1975; )  相似文献   

6.
Pure cultures of the coccolithophorid Syracosphaera carleraewere grown in a synthetic saline medium containing 3.4mM Ca++and 2.0, 1.0, 0.5 or 0.0 mM Sr++. The coccoliths were separatedby differential centrifugation, washed, dried, and examinedby flame photometry and by X-ray diffraction. In the absenceof Sr, they consisted of pure calcite. In media containing Sr,the concentration factor or incorporation factor (Sr/Ca in coccolithsSr/Ca in medium) was approx. 0.02 in each case, indicating ahigh degree of discrimination against Sr. 1 Nuna adreso: Scripps Instituto por Oceanografio, La Jolla,California, U. S. A. (Received March 4, 1961; )  相似文献   

7.
Membrane-bound Mg++-activated ATPase was separated from thelower epidermis of tobacco leaves (Nicotiand tabacum L. SamsunNN) on stepwise sucrose density gradient centrifugation. Membrane-bound epidermal ATPase was localized in the interfaceof densities in sucrose of 1.12 to 1.16 in the sedimentary fractionbetween 1,500?g to 10,000?g from the homogenate of the lowerepidermis. The epidermal ATPase activity was activated by divalentcations (Mg++>Mn++Co++>Fe++>Zn++>Ca++) and furtherstimulated by KCl by ca. 20%. The pH optimum for Mg++-activationof the epidermal ATPase was ca. 6.0. The enzyme hydrolyzed ATPmore rapidly than other nucleoside triphosphates. The optimumtemperature for activation of the epidermal ATPase activitywas ca. 40?C. 50% of the epidermal ATPase activity was lostin 18 min at 55?C and in 2.5 days at 2.5?C. The apparent Kmvalue of the epidermal ATPase was 4.7?10–4 M and Vmaxwas 65.4 nmoles Pi/mg protein/min. The epidermal ATPase wasstrongly inhibited by N, N'-dicyclohexylcarbodiimide (DCCD)in vitro whereas oligomycin, carbonyl cyanide m-chlorophenylhydrazone(CCGP), indoleacetic acid (IAA) and abscisic acid (ABA) wereinsensitive to the epidermal ATPase activity. (Received May 23, 1978; )  相似文献   

8.
Konjak phosphomannose isomerase was inactivated in a time-dependentprocess by metal binding agents, and the inactivated enzymewas instantaneously reactivated by adding such metal ions asZn++, Co++, Fe++, Mn++ and Cu++. However, neither Ca++ nor Mg++were effective for reactivation. Zn++, at a low concentration,brought about complete reactivation of the enzyme at pH 6–7. The EDTA-treated enzyme was more susceptible to heat denaturationwhen compared with the native enzyme, but the addition of variousmetal ions caused the recovery of the thermal stability of theEDTA-treated enzyme. The magnitude of the recovery dependedon the metal ion species and the concentrations. The most effectivemetal ion was Co++, which caused the recovery of thermal stabilityto a level higher than that of the native enzyme. Phosphomannoseisomerase was inhibited by pchloromercuribenzoate and HgCl2;the inhibition by p-chloromercuribenzoate being more pronouncedas incubation progressed. In contrast, the EDTA-treated enzymewas more readily inhibited by the mercurial ion than was thenative enzyme. Zn++, when added to the EDTA-treated enzyme,markedly restored its resistance to the mercurial-induced inhibition.The metal-substituted enzyme was also inhibited by EDTA in atime-dependent process. 1 This paper constitutes part 4 of studies on konjak mannanbiosynthesis. (Received March 3, 1975; )  相似文献   

9.
A double effect of Ca++ is observed on K+-absorption by Lemnaminor: activation through coupled (probably metabolic) processes,and inhibition through a perturbation of the structure of thecatalytical sites of K+-absorption. In contrast, Mg++, whichalso exhibits a structural inhibitory effect, has not apparentlya metabolic actrvatory one. It seems that diffusive processescould account partly for the second phase of the dual-phasecurves of absorption.  相似文献   

10.
For determination of the effects of polymyxin B, polymyxin E,or ethylenediamine tetra-acetic acid (EDTA) on plant cell membranes,the rates at which three solutes, K+, P1, and sugar, leakedfrom treated tissue culture cell suspensions of Nicotiana tabacumwere measured. The kinetics of leakage from cells treated witheither of the polymyxins was biphasic, whereas kinetics forcells treated with EDTA was monophasic. Only K+ leaked frompolymyxin-treated cells during the first phase, and all threesolutes leaked during the second phase. The slower first phaseis interpreted as leakage of K+ from the Donnan free space andcytoplasm, and the faster second phase as the leakage of solutesfrom the vacuole. The monophasic kinetics of EDTA treatmentindicated that solutes were leaking simultaneously from cytoplasmand vacuole. Of the divalent cations tested, only Ca++ and Mn++counteracted the effects of polymyxin and EDTA. Ca++ even restoredP1 and sugar uptake. Addition of Mg++ or Sr++ to polymyxin-treatedcells did not stop solute leakage but actually enhanced theleakage rates. A model is presented that suggests that polymyxinor EDTA induces solute leakage by forming pores in plant cellmembranes. The effects of divalent cations on membranes oncethe pores are formed are also discussed. Key words: Polymyxin, EDTA, Nicotiana tabacum, Solute leakage  相似文献   

11.
ATPase in isolated glycerinated flagella of Chlamydomonas snowiaeis shown to be inhibited by high ATP concentrations, by DNPat pH 6.0 and by salyrgan. The enzyme is activated by Mg++ andthe activation is reversed by Ca++. A number of other factorswhich can affect the phototactic behaviour of the cells do notaffect ATPase activity, indicating that the response of directionalmotility is under separate control in the intact cell. 1 This work is based on part of an M. Sc. thesis of I.C.-K.  相似文献   

12.
Cell-free extracts from soft rots of potato tubers caused byErwinia atroseptica and Corticium praticola readily caused cellseparation and loss of electrolytes in discs of potato tubers.Both were most rapid at pH and Ca++ ion concentration optimalfor the activity of a pectate trans-climinase in the E. atrosepticaextract and a pectate polygalacturonase in the C. praticolarot extract. Permeability changes and killing of protoplastsbut not cell separation were delayed when solutes at plasmolysingconcentrations were added to the solutions of the cell-separatingenzymes. The role of these enzymes in the permeability changesand killing of protoplasts is discussed.  相似文献   

13.
The hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, or cardiac (If)/neuronal (Ih) time- and voltage-dependent inward cation current channels, are conventionally considered as monovalent-selective channels. Recently we discovered that calcium ions can permeate through HCN4 and Ih channels in neurons. This raises the possibility of Ca2+ permeation in If, the Ih counterpart in cardiac myocytes, because of their structural homology. We performed simultaneous measurement of fura-2 Ca2+ signals and whole cell currents produced by HCN2 and HCN4 channels (the 2 cardiac isoforms present in ventricles) expressed in HEK293 cells and by If in rat ventricular myocytes. We observed Ca2+ influx when HCN/If channels were activated. Ca2+ influx was increased with stronger hyperpolarization or longer pulse duration. Cesium, an If channel blocker, inhibited If and Ca2+ influx at the same time. Quantitative analysis revealed that Ca2+ flux contributed to 0.5% of current produced by the HCN2 channel or If. The associated increase in Ca2+ influx was also observed in spontaneously hypertensive rat (SHR) myocytes in which If current density is higher than that of normotensive rat ventricle. In the absence of EGTA (a Ca2+ chelator), preactivation of If channels significantly reduced the action potential duration, and the effect was blocked by another selective If channel blocker, ZD-7288. In the presence of EGTA, however, preactivation of If channels had no effects on action potential duration. Our data extend our previous discovery of Ca2+ influx in Ih channels in neurons to If channels in cardiac myocytes. calcium ion flux; hyperpolarization-activated, cyclic nucleotide-gated/cardiac time- and volume-dependent cation current channels  相似文献   

14.
Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd- (FG, Cucurbita ficifolia Bouché)seedlings in order to determine the effect of solution temperature(12, 22, and 32°C) on the mineral composition of xylem sapand the plasma membrane K+-Mg++-ATPase activities of the roots.Low solution temperature (12°C) lowered the concentrationof NO3 and H2PO4 in xylem sap of CG plants butnot of FG plants. Concentrations of K+, Ca++ and Mg++ in xylemsap were less affected than anions by solution temperature.The plasma membrane of FG plants grown in 12°C solutiontemperature showed the highest K+- Mg++-ATPase activity at allATP concentrations up to 3 mM and at low reaction temperatureup to 12°C, indicating resistance of figleaf gourd to lowroot temperature. (Received December 27, 1994; Accepted March 10, 1995)  相似文献   

15.
Cell-free filtrates from cultures of Bacterium aroideae on asimple synthetic medium contained an enzyme, provisionally termeddepolymerase, which rapidly reduced the viscosity of pectinsolutions, and protopectinase which macerated slices of potatotuber tissue. These filtrates had little pectin-esterase activity. The activity of depolymerase was directly proportional to enzymeconcentration; the activity of protopectinase was approximatelyproportional to the square root of the enzyme concentration.Crude solutions were partially purified by acetone or ethanolprecipitation; ammonium sulphate was less satisfactory as aprecipitating agent. Enzyme preparations which rapidly reduced the viscosity of pectinand pectate solutions were relatively inactive when assayedfor polygalacturonase. activity by measuring reducing groupsliberated. After prolonged incubation some 20 and 40 per cent.hydrolysis of solutions of pectin and pectate respectively wasobtained. The pH optimum for depolymerase activity was near 9.0, the enzymewas activated by Ca++ but not by a number of other cations;the loss of activity following dialysis was largely restoredby adding Ca++. The enzyme was rapidly inactivated at temperaturesabove 60° C. and at pH 2.7. The properties of protopectinase generally resembled those ofdepolymerase. Analysis of the breakdown products following enzyme degradationof pectin and pectate solutions by paper chromatography showedthat galacturonic acid was not produced but that a number ofother products were formed, including one of fairly low molecularweight. The differences between the pectic enzymes of B. aroideae andthose from other sources, and the possible identity of depolymerase,polygalacturonase, and protopectinase are discussed.  相似文献   

16.
NADP-specific isocitrate dehydrogenase from the soluble fractionof maturing castor bean endosperm was partially purified (approximately180-fold) and some of its enzymatic properties were studied.Mg++, Mn++, Cd++, Ba++, Co++, Zn++, and Sr++ were activatorsof the enzyme reaction at a concentration of 6.7x10 M. The optimumpH of this enzyme was about 8.5. The enzyme was stable in thenarrow range from pH 7.0 to pH 8.0. Km values for isocitrateand NADP at pH 8.5 were 3.5x10–6 M and 3.6x10–6M, respectively. Enzyme stability was not affected by NaCl concentrationand enzyme reaction was inhibited at 5x10–6 M PCMB (80%inhibition). It is suggested that the condensation product ofglyoxylate and oxalacetate also inhibits the reaction. NADP-IDHin the crude extract from maturing castor bean endosperm washeat-stable but the dialyzed enzyme preparation and the partiallypurified enzyme were labile against heat treatment at 57°C.When Mg++ was added to the partially purified enzyme in thepresence of isocitrate or NADP, the enzyme was stabilized againstheat treatment. Mn++, Ca++, Co++, Sr++ or Ba++ could be substitutedfor Mg++. Addition of only one of the factors, Mg++, isocitrateor NADP, had no effect on the heat stability. Moreover, a combinationof isocitrate and NADP did not establish stabilization. A divalentcation plays a central role, while adenine nucleotide, especiallyATP, may have an important part in stabilization. (Received August 14, 1972; )  相似文献   

17.
Agonist stimulation of human pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) with histamine showed similar spatiotemporal patterns of Ca2+ release. Both sustained elevation and oscillatory patterns of changes in cytosolic Ca2+ concentration ([Ca2+]cyt) were observed in the absence of extracellular Ca2+. Capacitative Ca2+ entry (CCE) was induced in PASMC and PAEC by passive depletion of intracellular Ca2+ stores with 10 µM cyclopiazonic acid (CPA; 15–30 min). The pyrazole derivative BTP2 inhibited CPA-activated Ca2+ influx, suggesting that depletion of CPA-sensitive internal stores is sufficient to induce CCE in both PASMC and PAEC. The recourse of histamine-mediated Ca2+ release was examined after exposure of cells to CPA, thapsigargin, caffeine, ryanodine, FCCP, or bafilomycin. In PASMC bathed in Ca2+-free solution, treatment with CPA almost abolished histamine-induced rises in [Ca2+]cyt. In PAEC bathed in Ca2+-free solution, however, treatment with CPA eliminated histamine-induced sustained and oscillatory rises in [Ca2+]cyt but did not affect initial transient increase in [Ca2+]cyt. Furthermore, treatment of PAEC with a combination of CPA (or thapsigargin) and caffeine (and ryanodine), FCCP, or bafilomycin did not abolish histamine-induced transient [Ca2+]cyt increases. These observations indicate that 1) depletion of CPA-sensitive stores is sufficient to cause CCE in both PASMC and PAEC; 2) induction of CCE in PAEC does not require depletion of all internal Ca2+ stores; 3) the histamine-releasable internal stores in PASMC are mainly CPA-sensitive stores; 4) PAEC, in addition to a CPA-sensitive functional pool, contain other stores insensitive to CPA, thapsigargin, caffeine, ryanodine, FCCP, and bafilomycin; and 5) although the CPA-insensitive stores in PAEC may not contribute to CCE, they contribute to histamine-mediated Ca2+ release. intracellular calcium stores; oscillations; pulmonary hypertension  相似文献   

18.
The activity of shikimate: NADP oxidoreductase [EC 1. 1. 1.25] in sweet potato root tissue increased soon after slicing.Enzyme preparations obtained from both sliced tissue and fromfresh tissue probably contained a single enzyme component, andthey showed identical chromatographical behaviour. Km values of the enzyme for NADP and shikimate were 1.0x10–4Mand 1.3 x 10–3M, respectively. Enzyme activity was potentlyinhibited by SH-inhibitors such as p-chloromercuribenzoate andoxidized glutathione. Enzyme activity was affected neither by mononucleotides suchas ATP, ADP and AMP, divalent cations, Mg++, Ca++ and Mn++,nor by metabolites such as tryptophan, phenylalanine, tyrosineand t-cinnamic acid which are involved in aromatic compoundsyntheses. The enzyme rapidly lost its activity. This inactivation reactionshowed a time course consisting of two steps of the first-orderreaction. The inactivated enzyme preparation was not reactivatedby thiol compounds such as cysteine, 2-mercaptoethanol and glutathione,although these reagents, to a certain extent, protected theenzyme from inactivation. The results suggest that denaturationof the enzyme protein was involved in inactivation of the enzyme. 1Part 74 of the phytopathological chemistry of sweet potatowith black rot and injury. 2Present address: Department of Biology, Faculty of Science,Tokyo Metropolitan University, Setagaya-ku, Tokyo. (Received August 5, 1968; )  相似文献   

19.
The effect of Ca++ on various parameters of apple fruit senescencewas investigated. Distinct and specific changes in polypeptideand phosphoprotein patterns were observed in Ca++ treated ascompared to control fruits. A 70 kDa salt-extracted polypeptidebecame apparent in control fruits after 8 months of cold storagewhich was not apparent in Ca++-treated fruits until 12 months.The soluble protein profile of Ca++-treated fruits showed anaccumulation of a 30 kDa polypeptide while the control fruitsaccumulated a 60 kDa polypeptide. Autoradiographs of phosphorylatedpolypeptides revealed a 60 kDa membrane polypeptide becomingphosphorylated in the Ca++-treated and not in the control fruitprotein fractions. Transmission electron micrographs of thecell showed Ca++ to be effective in maintaining the cell wallstructure, particularly the middle lamella. Furthermore, increasein fruit Ca++ reduced CO2 and C2H2 evolution and altered chlorophyllcontent, ascorbic acid level and hydraulic permeability. 1Scientific Paper No: 7930, College of Agriculture and HomeEconomics Research Center, Washington State University, Pullman,Washington, Project 0321. 2Supported by grants from the National Science Foundation CB-8502215and Washington State Tree Fruit Research Commission to BWP. (Received September 3, 1987; Accepted March 3, 1988)  相似文献   

20.
FALADE  J. A. 《Annals of botany》1973,37(2):345-353
The uptake of potassium, calcium, and magnesium ions by maizeand the interrelationships among the cations have been investigatedat 48 K: Ca: Mg ratios in culture solutions. Calcium was foundto stimulate K+ and Mg++ uptake at certain cation ratios butinhibit it at others. Potassium did the same for Ca++ uptake,and Mg++ for Ca++ and K+. The uptake of Mg++ was generally enhancedby K+. The sum of the cations in the plants expressed in meqwas fairly constant for treatments of the same K+ concentrationat the low to moderate levels of K+, but at considerably higher(> 24 meq l–1) K+ levels the constancy was not dependenton K+ concentration. Potassium depressed, but Mg++ stimulatedphosphorus accumulation. Calcium stimulated phosphate absorptionat certain cation ratios but had no effect at others. The plantyield increased with increasing K+ up to 24 meq l–1 ofK+ after which the yield tended to fall with further increasein K+. The yield was also increased by Ca++. Magnesium increasedthe yield at certain cation ratios and either depressed it orwas without effect at others.  相似文献   

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