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1.
The purified mucilage from Opuntia ficus-indica is a high MW polysaccharide which behaves as a polyelectrolyte. Viscosity of its solution is dependent on the Ca 2+ ion concentration and on pH, being greatest at alkaline pH. The sedimentation coefficient was dependent on concentration. The molecule had an estimated axial ratio of 256 in water, and this was reduced at low pH and in the presence of high concentrations of Ca 2+. The molecule was studied with light scattering and CD techniques and its UV spectrum was recorded. All these parameters were influenced by pH and by ion concentration. The gelation properties also changed with pH and with Ca 2+ giving dense gels in its presence and loose ones in its absence. The results are interpreted in terms of changes in conformation of the molecule, changes in Ca 2+ binding and degree of ionization of the molecule. An attempt is made to relate the molecular properties to the physiological function of the mucilage in the calcium and water economy of the plant. 相似文献
2.
The water-soluble, acidic polysaccharide isolated from the coccoliths of the alga Emiliania huxleyi (Lohmann) Kamptner contains residues of the following sugars: l-galactose, d-glucose, d-mannose, l-mannose, l-rhamnose, l-arabinose, d-ribose, d-xylose, 6- O-methyl-d-mannose, 6- O-methyl-l-mannose, 2,3-di- O-methyl-l-rhamnose, 3- O-methyl-d-xylose, and d-galacturonic acid. l-Mannose, 6- O-methyl-d-mannose, 6- O-methyl-l-mannose, and 2,3-di- O-methyl-l-rhamnose are novel constituents of a polysaccharide. In addition, the presence of sulphate groups was found. Galacturonic acid and sulphate in the polysaccharide bind Ca 2+ ions apparently in a ratio of one mol of Ca 2+ per mol of acidic residue. This feature is relevant for the proposed matrix function of the polysaccharide in the formation of the calcified cell-wall plates (coccoliths) of the alga. 相似文献
3.
In the presence of MgCl 2 and ATP, the specific viscosity of suspensions of unsealed freezethawed erythrocyte membranes decreased slowly with time at 37 °C. The decrease in viscosity was found to be an index of Mg-ATP-specific induced folding of these membranes. Mg-ATP-dependent shape or viscosity changes were found to be highly temperature dependent and the viscosity of these membranes did not decrease in the presence of 2 mm 5′-adenyl imidodiphosphate and MgCl 2. Cyclic AMP, NaCl, or KCl did not have any effect on the rate of Mg-ATP-induced viscosity decreases. The Mg-ATP-dependent viscosity decreases were inhibited 100% by 1 mm chlorpromazine or 1 mm N-ethylmaleimide. Mg-ATP-dependent viscosity decreases were half-maximally inhibited by 1 μm Ca 2+ and completely inhibited by 3–5 μm Ca 2+. Ca 2+ (5 μm) also inhibited Mg 2+-dependent phosphorylation 25 to 30% in these membranes. However, if these membranes were preincubated in the absence of Ca 2+ for greater than 10 min at 37 °C, 5 μm Ca 2+ no longer inhibited Mg-ATP-dependent viscosity decreases and only inhibited Mg 2+-dependent phosphorylation 5% in these preincubated membranes. Preincubation of these membranes at 37 °C for 10 min in the absence of Ca 2+ also resulted in the loss of approximately 40 to 50% of the high-Ca 2+ affinity Ca + Mg-ATPase activity. The presence of 5 μm Ca 2+ in the preincubation medium protected against the loss of the inhibitory effect of Ca 2+ on Mg 2+-dependent phosphorylation and Mg-ATP-dependent viscosity decreases. The presence of Ca 2+ in the preincubation medium also protected against the loss of Ca + Mg-ATPase activity in these membranes. It is hypothesized that freeze-thawed erythrocyte membranes contain a Ca 2+ phosphatase activity which is temperature labile in the absence of Ca 2+ and that this Ca 2+ phosphatase activity may be involved in the regulation of shape of these membranes. Also discussed is the possible relationship of this Ca 2+ phosphatase with Ca + Mg-ATPase activity and the problems inherent in studying Ca 2+-regulated functions in freeze-thawed erythrocyte membranes. 相似文献
4.
The lipid distribution in binary mixed membranes containing charged and uncharged lipids and the effect of Ca 2+ and polylysine on the lipid organization was studied by the spin label technique. Dipalmitoyl phosphatidic acid was the charged, and spin labelled dipalmitoyl lecithin was the uncharged (zwitterionic) component. The ESR spectra were analyzed in terms of the spin exchange frequency, Wex. By measuring Wex as a function of the molar percentage of labelled lecithin a distinction between a random and a heterogeneous lipid distribution could be made. It is established that mixed lecithinphosphatidic acid membranes exhibit lipid segregation (or a miscibility gap) in the fluid state. Comparative experiments with bilayer and monolayer membranes strongly suggest a lateral lipid segregation. At low lecithin concentration, aggregates containing between 25% and 40% lecithin are formed in the fluid phosphatidic acid membrane. This phase separation in membranes containing charged lipids is understandable on the basis of the Gouy-Chapman theory of electric double layers.In dipalmitoyl lecithin and in dimyristoyl phosphatidylethanolamine membranes the labelled lecithin is randomly distributed above the phase transition and has a coefficient of lateral diffusion of D = 2.8·10 ?8 cm 2/s at 59°C.Addition of Ca 2+ dramatically increases the extent of phase separation in lecithin-phosphatidic acid membranes. This chemically (and isothermally) induced phase separation is caused by the formation of crystalline patches of the Ca 2+-bound phosphatidic acid. Lecithin is squeezed out from these patches of rigid lipid. The observed dependence of Wex on the Ca 2+ concentration could be interpreted quantitatively on the basis of a two-cluster model. At low lecithin and Ca 2+ concentration clusters containing about 30 mol% lecithin are formed. At high lecithin or Ca 2+ concentrations a second type of precipitation containing 100% lecithin starts to form in addition. A one-to-one binding of divalent ions and phosphatidic acid at pH 9 was assumed. Such a one-to-one binding at pH 9 was established for the case of Mn 2+ using ESR spectroscopy.Polylysine leads to the same strong increase in the lecithin segregation as Ca 2+. The transition of the phosphatidic acid bound by the polypeptide is shifted from Tt = 47.5° to Tt = 62°C. This finding suggests the possibility of cooperative conformational changes in the lipid matrix and in the surface proteins in biological membranes. 相似文献
5.
Nicotinic acid adenine dinucleotide phosphate (NAADP) mobilizes Ca 2+ through a mechanism totally independent of cyclic ADP-ribose or inositol trisphosphate. Fluorescent analogs of NAADP were synthesized in this study to facilitate further characterization of this novel Ca 2+ release mechanism. The base-exchange reaction catalyzed by ADP-ribosyl cyclase was utilized to convert nicotinamide 1, N6-ethenoadenine dinucleotide phosphate to a fluorescent product, nicotinic acid 1, N6-ethenoadenine dinucleotide phosphate (etheno-NAADP). The excitation spectrum of the product showed two maxima at 275 nm and 300 nm and an emission maximum at 410 nm. An aza derivative of etheno-NAADP was also synthesized by sequential treatments with NaOH and nitrite. The product, nicotinic acid 1, N6-etheno-2-aza-adenine dinucleotide phosphate (etheno-aza-NAADP) had excitation maxima at 280 nm and 360 nm and an emission maximum at 470 nm. The fluorescence of both analogs was sensitive to polarity and exhibited a 3–4-fold enhancement going from an aqueous buffer to an organic solvent. Proton-NMR measurements confirmed the presence of the etheno ring in both analogs. In the aza derivative the proton at the 2-position of the adenine ring was absent, consistent with the conversion of the 2-carbon to a nitrogen. Both analogs could activate Ca 2+ release from sea urchin egg homogenates and the half-maximal concentrations for etheno-aza-NAADP and etheno-NAADP were at about 2.5 μM and 5 μM, respectively. At sub-threshold concentrations, both analogs could also function as antagonists, inactivating the NAADP-sensitive Ca 2+ release with a half-maximal concentration of 60–80 nM. Microinjection of etheno-aza-NAADP into live eggs activated Ca 2+ increase and triggered a cortical exocytotic reaction confirming its effectiveness in vivo. These fluorescent analogs are potentially useful for visualizing the novel Ca 2+ stores that are sensitive to NAADP in live cells. 相似文献
6.
The transport of serine into tobacco cells ( Nicotiana tabacum L.) cultured in liquid medium was examined. Transport was inhibited approximately 50% by 2,4-dichlorophenoxyacetic acid, indoleacetic acid, α-naphthalene acetic acid, and kinetin at a concentration of 10 micrograms per milliliter. Transport was not inhibited by 2,6-dichlorophenoxyacetic acid and inhibited less than 25% by p-chlorophenoxyacetic acid at this concentration. Removal of 2,4-dichlorophenoxyacetic acid from the transport medium resulted in an alleviation of inhibition. Gibberellic acid at concentrations from 2 to 20 micrograms per milliliter stimulated transport. It was previously shown that inhibition of transport by La3+ was due to removal of Ca2+ from surface sites and inhibition of Ca2+ uptake by cells. None of the growth regulators tested had any significant effect on Ca2+ binding and/or transport. A contributing factor to the low transport rates in the absence of Ca2+ is the increased rate of serine efflux. None of the growth regulators tested had any significant effect on the rate of serine efflux. 相似文献
7.
The hen oviduct shell gland is a highly active calcium-transporting epithelial tissue which is responsible for the mineralization of the egg shell. We have identified a calcium-stimulated ATPase present at high specific activity in membrane preparations from shell gland mucosal shavings. In the presence of optimal MgCl 2 (5 mm) and a Ca 2+ buffer, ATP hydrolysis was stimulated by addition of low concentrations of free Ca 2+ ( K0.5 ~0.4 μm); but not by similar concentrations of Mn 2+, Zn 2+, Co 2+, or La 2+. This stimulation was specific for ATP; there was little or no effect of Ca 2+ on hydrolysis of ADP, AMP, GTP, ITP, or p-nitrophenyl phosphate. Calcium-stimulated ATPase activity was inhibited by chlorpromazine, trifluoperazine, and quercetin, as well as by sulfhydryl-blocking agents, but not by oligomycin or ouabain. No significant effect of calmodulin was observed. Finally, low concentrations of free Ca 2+ (10 to 100 μm) in the presence or absence of Mg 2+ stimulated transfer of 32P from [γ- 32P]ATP to a 105,000 molecular weight shell gland membrane protein. This phosphoprotein was sensitive to hydrolysis by heating or by hydroxylamine treatment at acidic pH, and its formation was not inhibited by addition of K +. The specific activity of Ca 2+-ATPase in total membrane preparations from laying hen shell gland ranged from 80 to 150 nmol/min/ mg protein, similar to or greater than levels found in purified plasma membrane fractions from a variety of tissues. No significant activity was found in membrane preparations from the magnum or isthmus regions of the oviduct, which are not involved in egg shell calcification. The characteristics of the Ca 2+-ATPase, its high specific activity, and its preferential localization in the shell gland region of the oviduct suggest a role for an ATP-dependent calcium transport system in egg shell mineralization. 相似文献
8.
The characteristics of Ca 2+ transport into endoplasmic reticulum vesicles isolated from roots of Lepidium sativum L. cv Krause have been investigated. The concentration of free Ca 2+ and ATP needed for half-maximal activity were 2.5 and 73 micromolar, respectively, and the enzyme obeyed Michaelis-Menten-like kinetics. The pH maximum occurred at 7.5 and the activity was greatly reduced at either pH 7.0 or 8.0. The Ca2+-dependent modulation protein, calmodulin, was tested for its effect on Ca2+ transport into endoplasmic reticulum vesicles. Although the phenothiazine inhibitors chlorpromazine, fluphenazine, and trifluoperazine all inhibited Ca2+ transport activity with a half-maximal effect at approximately 35 micromolar, authentic bovine brain calmodulin did not alter the activity at concentrations of 0.5 to 8 micrograms per milliliter. Calmodulin also showed no influence on the time-dependent accumulation of Ca2+ into vesicles. The membranes did not contain endogenously bound calmodulin since washing with (ethylenebis[oxyethylenenitrile])tetraacetic acid or fluphenazine, treatments which disrupt calmodulin binding, did not alter Ca2+ transport activity. The inhibition of Ca2+ transport by phenothiazine drugs was likely related to their nonspecific interaction with the membrane. Thus, there was no indication that calmodulin regulated Ca2+ uptake into root endoplasmic reticulum. 相似文献
9.
The decline in ethylene production in apple ( Pyrus malus L. cv. Golden Delicious) tissue slices during 24 hours incubation in 600 millimolar sorbitol and 10 millimolar 2-( N-morpholino)ethanesulfonic acid buffer (pH 6.0) is recognized as a senescent phenomenon. The inclusion of very high concentrations (100 millimolar) of Ca 2+, Mg 2+, or Ca 2+ plus Mg 2+ severely inhibited ethylene production during the first 6 hours of incubation. However, after 6 hours and up to 24 hours the ethylene-forming system was stablized. These high concentrations of Ca 2+, Mg 2+, or Ca 2+ plus Mg 2+ virtually eliminated lipid peroxidation and protein leakage from these slices. Also conversion of 1-aminocyclopropane-1-carboxylic-1-acid to ethylene and the influence of indoleacetic acid on ethylene production was stabilized after 24 hours of incubation by these high concentrations of Ca 2+, Mg 2+, and Ca 2+ plus Mg 2+. Addition of divalent ionophores severely inhibited ethylene production, but this inhibition was prevented by Ca 2+ in concentrations greater than the ionophore. These data suggest that the loss of ethylene production by aging tissue slices results from degradation of membranes. They support previous work that indicates that the ethylene-forming system, perhaps the segment of the pathway from 1-aminocyclo-propane-1-carboxylic-1-acid to ethylene, resides in the plasma membrane. 相似文献
10.
The effect of archidonic, oleic and linoleic acid on calcium uptake and release by sarcoplasmic reticulum isolated from longissimus dorsi muscle was investigated using a Ca 2+ electrode. All three long chain fatty acids stimulated the release of Ca 2+ from sacroplasmic reticulum when added after exogenous Ca 2+ was accumulated by the vesicles, and also inhibited Ca 2+ uptake when added before Ca 2+. This inhibitory effect on the calcium transport by arachidonic, oleic and linoleic acid was prevented by bovine serum albumin through its ability to bind with the fatty acid. The order of effectiveness of the fatty acids in inhibiting calcium transport by isolated sarcoplasmic reticulum was linoleic acid. Similar inhibition of calcium uptake and induction of calcium release by arachidonic acid was observed in muscle homogenate sarcoplasmic reticulum preparations. Both arachidonic and oleic acid stimulated the (Ca 2+ + Mg 2+)-ATPase activity of sarcoplasmic reticulum at low concentrations, but inhibited the (Ca 2+ + Mg 2+)-ATPase activity at high concentrations. The maximal (Ca 2+ + Mg 2+-ATPase activity observed with arachidonic acid was twice that obtained with oleic acid, but the concentration of arachidonic acid required was 3–4-times greater than that of oleic acid. The concentration of arachidonic acid required to give maximum stimulation of the (Ca 2+ + Mg 2+)-ATPase activity was 3.6-times greater than that needed for complete inhibition of calcium accumulation by the sacroplasmic reticulum. With oleic acid, however, the concentration required to give maximum stimulation of the (Ca 2+ + Mg 2+)-ATPase activity inhibited the sarcoplasmic reticulum Ca 2+ accumulation by 72%. The present data support our hypothesis that, in porcine malignant hyperthermia, unsaturated fatty acids from mitochondrial membranes released by endogenous phospholipase A 2 would induce the sarcoplasmic reticulum to release calcium (Cheah K.S. and Cheah, A.M. (1981) Biochim. Biophys. Acta 634, 70–84). 相似文献
11.
In the presence of 1.0 mM ATP and MgCl 2, the specific viscosity of suspensions of human erythrocyte ghosts decreases 35% in 20 minutes at 22°C. The changes in viscosity are a sensitive index of Mg-ATP dependent shape changes in these membranes. Low concentrations of Ca 2+ (1 to 5 μM) inhibit Mg-ATP dependent viscosity changes. If ghosts were preincubated with 1 mM Mg-ATP and 20 μM A23187 to produce a maximal decrease in viscosity, addition of 10 μM Ca 2+ to the preincubated ghosts increased the viscosity to levels observed in ghosts preincubated without ATP. Ca 2+ (1 to 5 μM) also inhibited Mg 2+ dependent phosphorylation 30% and stimulated dephosphorylation 25% in ghost membranes. These effects of Ca 2+ on viscosity and phosphorylation may be due to a membrane bound Ca 2+ phosphatase activity which dephosphorylates membranes phosphorylated by a Mg 2+ dependent kinase activity. 相似文献
12.
Since the increasing prevalence of obesity is one of the major health problems of the modern era, understanding the mechanisms of oro-gustatory detection of dietary fat is critical for the prevention and treatment of obesity. We have conducted the present study on Psammomys obesus, the rodent desert gerbil which is a unique polygenic natural animal model of obesity. Our results show that obese animals exhibit a strong preference for lipid solutions in a two-bottle test. Interestingly, the expression of CD36, a lipido-receptor, in taste buds cells (TBC), isolated from circumvallate papillae, was decreased at mRNA level, but remained unaltered at protein level, in obese animals. We further studied the effects of linoleic acid (LA), a long-chain fatty acid, on the increases in free intracellular calcium (Ca 2+) concentrations, [Ca 2+]i, in the TBC of P. obesus. LA induced increases in [Ca 2+]i, largely via CD36, from intracellular pool, followed by the opening of store-operated Ca 2+ (SOC) channels in the TBC of these animals. The action of this fatty acid on the increases in [Ca 2+]i was higher in obese animals than that in controls. However, the release of Ca 2+ from intracellular stores, studied also by employing thapsigargin, was lower in TBC of obese animals than control rodents. In this study, we show, for the first time, that increased lipid intake and altered Ca 2+ signaling in TBC are associated with obesity in Psammomys obesus. 相似文献
13.
The binding of cAMP to the chemotactic cAMP receptor in intact Dictyostelium discoideum cells and isolated membranes is strongly inhibited by unsaturated fatty acids. In isolated membranes, cis-unsaturated fatty acids decreased the number of accessible cAMP binding sites, without significantly altering their affinity. Most potent were C 18 and C 20 cis-poly unsaturated fatty acids, like arachidonic acid, linoleic acid and linolenic acid. Trans-unsaturated fatty acid was less potent than its cis isomer, while saturated fatty acids did not affect the binding of cAMP to receptors at all. Oxidation reactions were not important for the effect of unsaturated fatty acids. When membranes were preincubated with millimolar concentrations of Ca 2+, the effect of unsaturated fatty acids was strongly diminished. Mg 2+ was ineffective. Ca 2+, if presented after the incubation of membranes with unsaturated fatty acids, did not reverse the inhibitory effect. The specificity of the fatty acid effect, and the interference with Ca 2+, but not Mg 2+, suggest that the properties of the cAMP receptor are changed as a result of alterations in the lipid bilayer structure of the membrane. 相似文献
14.
Assessment of the regulation of plant metabolism by the calcium ion requires a knowledge of its intracellular levels and dynamics. Technical problems have prevented direct measurement of the concentration of intracellular Ca 2+ in plant cells in all but a few cases. In this study we show that electropermeabilized protoplasts of Daucus carota and Hordeum vulgare took up the Ca 2+ indicating fluorescent dye methoxyquinoline( O-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid (Quin-2) and the Ca 2+ indicating photoprotein, aequorin. These protoplasts subsequently recovered their plasma membrane integrity. However, up to 10% of intracellularly trapped Quin-2 was associated with a protoplast vacuolar fraction. Also, Quin-2 loading reduced total ATP levels by approximately 60% and inhibited subsequent protoplast division whereas aequorin loading reduced ATP content by only 20% and did not prevent division. Therefore, the basal cytoplasmic Ca 2+ level measured with aequorin (less than 200 nanomolar) may more reliably reflect that found in vivo in the unperturbed protoplast than that measured with Quin-2 (120-360 nanomolar). However, measurements made with aequorin were found to be inaccurate at Ca 2+ levels below 200 nanomolar, Quin-2 proving complementary in indicating these low Ca 2+ concentrations. Cytosolic Ca 2+ was observed to increase on treatment with azide and silver ions. 相似文献
15.
Though most of the studies have focused on the effects of free fatty acids on T-cell activation, fatty acids incorporated into plasma membrane phospholipids may also affect cell signaling via diacylglycerol (DAG), generally produced by phospholipid hydrolysis. In the present study, we have synthesized a DAG-containing oleic acid and studied its implication in the modulation of calcium signaling in human Jurkat T-cells. 1-palmitoyl-2-oleoyl- sn-glycerol (POG) induced a dose-dependent increase in [Ca 2+] i. This effect was due to the presence of oleic acid at the sn-2 position as no differences were observed between POG and 1-stearoly-2-oleoyl- sn-glycerol (SOG). However, the substitution of oleic acid with arachidonic acid at the sn-2 position of the DAG moiety exerted a different response on the increases in [Ca 2+] i in these cells. POG-evoked increases in [Ca 2+] i were not due to its metabolites. Furthermore, POG-induced increases in [Ca 2+] i were due to the opening of TRPC3/TRPC6 channels as silencing of TRPC3 and TRPC6 genes by shRNA abolished calcium entry. Moreover, disruption of lipid rafts with methyl-β-cyclodextrin completely abolished POG-evoked increases in [Ca 2+] i. In conclusion, our results demonstrate that oleic acid can influence T-lymphocyte functions, in the conjugated form of DAG, via opening TRPC3/6 channels. 相似文献
16.
The (Ca 2+ + Mg 2+)-dependent ATPase (ATP phosphohydrolase, EC 3.6.1.3) from human erythrocytes occurred in two different states, A-state and B-state, depending on the membrane preparation.The A-state showed low maximum activity ( V) and the Ca 2+ activation was characterized by a Hill coefficient, nH, of about 1 and a Michaelis constant, KCa, about 30 μM.The B-state showed high V, a nH above 1, which indicates positive cooper-activity of Ca 2+ activation, and a KCa of about 1 μM.With varying ATP concentrations, both the A-state and the B-state showed negative cooperativity and slightly different values of Km.The B-state was shifted to the A-state when the membranes were exposed to low Ca 2+ concentrations. The shift reached 50% at approx. 0.5 μM Ca 2+. At the low Ca 2+ concentrations an activator was released from the membranes.The A-state was shifted to the B-state when the membranes were exposed to Ca 2+ in the presence of the activator. The shift reached 50% at about 30 μM Ca 2+. The recovery of high V was time dependent and lasted several minutes. Increasing concentrations of Ca 2+ and activator accelerated the recovery.It is suggested that the A-state and the B-state correspond to enzyme free of activator and enzyme associated with activator, respectively. Furthermore, the two states may represent a resting and an active state, respectively, of the calcium pump. 相似文献
17.
The divalent cation selective ionophores A23187 and ionomycin were compared for their effects on the Ca 2+ contents, nucleotide contents, and protein synthetic rates of several types of cultured cells. Both ionophores reduced amino acid incorporation by approximately 85% at low concentrations (50–300 nmol/L) in cultured mammalian cells without reducing ATP or GTP contents. At these concentrations A23187 and ionomycin each promoted substantial Ca 2+ efflux, whereas at higher concentrations a large influx of the cation was observed. Ca 2+ influx occurred at lower ionophore concentrations and to greater extents in C6 glioma and P3X63Ag8 myeloma than in GH 3 pituitary cells. The ATP and GTP contents of the cells and their ability to adhere to growth surfaces declined sharply at ionophore concentrations producing increased Ca 2+ influx. Prominent reductions of nucleotide contents occurred in EGTA-containing media that were further accentuated by extracellular Ca 2+. Ionomycin produced more Ca 2+ influx and nucleotide decline than comparable concentrations of A23187. The inhibition of amino acid incorporation and mobilization of cell-associated Ca 2+ by ionomycin were readily reversed in GH 3 cells by fatty acid-free bovine serum albumin, whereas the effects of A23187 were only partially reversed. Amino acid incorporation was further suppressed by ionophore concentrations depleting nucleotide contents. Mitochondrial uncouplers potentiated Ca 2+ accumulation in response to both ionophores. At cytotoxic concentrations Lubrol PX abolished protein synthesis but did not cause Ca 2+ influx. Nucleotide depletion at high ionophore concentrations is proposed to result from increased plasmalemmal Ca 2+-ATPase activity and dissipation of mitochondrial proton gradients and to cause intracellular Ca 2+ accumulation. Increased Ca 2+ contents in response to Ca 2+ ionophores are proposed as an indicator of ionophore-induced cytotoxicity.Abbreviations BSA
bovine serum albumin
- EGTA
[ethylenebis(oxyethylenenitrilo)]tetraacetic acid
- PKR
double-stranded RNA-regulated protein kinase
- ER
endoplasmic reticulum
- eIF
eukaryotic initiation factor 相似文献
18.
Clostridium cylindrosporum spores germinated rapidly under reducing conditions when bicarbonate, uric acid, and calcium were present. Germination rates on 10 mM urate increased with increasing Ca 2+ (maximum rate at 5 mM Ca 2+ or greater). Germination rates on urate (limiting Ca 2+) increased with increasing urate concentrations to 10 mM urate. At 10 mM Ca 2+, germination rates reached a maximum at 1 mM urate and remained constant thereafter. Cations (Na +, K +, Li +, and Mg 2+), purines, purine analogs, and EDTA inhibited germination at limiting calcium concentrations but not (except for 10 mM adenine) at 10 mM Ca 2+. Methyl viologen or formate did not inhibit germination. Germination was not observed in solutions containing xanthine, hypoxanthine, caffeine, theophylline, 6,8-dihydroxypurine, adenine, allopurinol, formate, glycine, or acetate, even though some of the purines are growth substrates. 相似文献
19.
Tryptophan 5-monooxygenase in rat brainstem cytosol was activated about twofold by incubation with 0.5 mm ATP and 5 mm MgCl 2. The activation required micromolar concentrations of Ca 2+ but was not dependent on either cyclic AMP or cyclic GMP. Rat brain cytosol was shown to possess an endogenous protein kinase which was markedly stimulated by the addition of Ca 2+ using endogenous protein substrates. Following activation by ATP and Mg 2+ in the presence of Ca 2+, tryptophan 5-monooxygenase was reversibly deactivated to the original level by incubation at 30 °C after removal of Ca 2+ by adding ethylene glycol bis(β-aminoethyl ether) N,N′-tetraacetic acid and was then reactivated by incubation at 30 °C after subsequent addition of Ca 2+ and ATP. The deactivation was markedly inhibited by the omission of Mg 2+ or by the addition of NaF. 相似文献
20.
Stress ethylene production in bean ( Phaseolus vulgaris L., cv. Taylor's Horticultural) leaf tissue was stimulated by Cd 2+ at concentrations above 1 micromolar. Cd 2+-induced ethylene biosynthesis was dependent upon synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase. Activity of ACC synthase and ethylene production rate peaked at 8 h of treatment. The subsequent decline in enzyme activity was most likely due to inactivation of the enzyme by Cd 2+, which inhibited ACC synthase activity in vitro at concentrations as low as 0.1 micromolar. Decrease in ethylene production rate was accompanied by leakage of solutes and increasing inhibition of ACC-dependent ethylene production. Ca 2+, present during a 2-hour preincubation, reduced the effect of Cd 2+ on leakage and ACC conversion. This suggests that Cd 2+ exerts its toxicity through membrane damage and inactivation of enzymes. The possibility of an indirect stimulation of ethylene biosynthesis through a wound signal from injured cells is discussed. 相似文献
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