共查询到20条相似文献,搜索用时 15 毫秒
1.
Soluble and mitochondrial malic dehydrogenases (MDH) were isolated from root tips of the halophyte Tamarix tetragyna L. grown in the presence and absence of NaCl. The activity of the enzymes isolated from root tips grown in the presence of NaCl was lower than that of the enzymes isolated from roots grown in absence of NaCl. The mitochondrial MDH was much more sensitive to salinity than the soluble MDH. The soluble enzyme from roots grown in NaCl had a higher Km for malate and lower Km for NAD than enzyme from the control roots. Addition of NaCl in vitro at 72 mM significantly stimulated the reductive activity of soluble MDH, while higher NaCl concentrations (240 mM and above) depressed enzyme activity. The inhibition of enzyme activity by various salts was found to be in the order MgCl2 > NaCl = KCl > Na2SO4. Mannitol at equiosmotic concentrations had no effect. Substrate inhibition, typical for oxaloacetate oxidation, was not observed at high NaCl concentrations in vitro and high substrate concentrations neutralized the inhibitory effect of NaCl. Increased coenzyme concentrations had no effect. In vitro NaCl increased the Km for malate and oxaloacetate already at relatively low concentrations. At the same time NaCl decreased the Km for NAD and NADH. The inhibitory effect of NaCl on enzyme activity seems not to be due to the effect on the Km alone. Soluble and mitochondrial MDH had different responses to pH changes, mitochondrial MDH being more sensitive. Mitochondrial MDH released from the particles had a similar response to that of the entire particles. Changes of pH modified the effect of NaCl on enzyme activity. It was postulated that NaCl apparently induces conformational changes in the enzyme. 相似文献
2.
Regulation of Photosynthetic Electron Transport in Intact Spinach Chloroplasts: II. MECHANISM OF SALT-INDUCED INCREASE IN OXALOACETATE PHOTOREDUCTION
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The main focus of this study was to determine the mechanism by which certain exogenous monovalent salts stimulate rates of net O2 evolution linked to oxaloacetate reduction in intact spinach chloroplasts. The influence of salts on the dicarboxylate translocator involved in the transport of oxaloacetate and on the activity and activation of the chloroplast enzyme NADP-malate dehydrogenase, which mediates electron transport to oxaloacetate, was examined. High concentrations of KCl (155 millimolar) increased the apparent Km for oxaloacetate but did not significantly alter the maximal velocity of uptake. Likewise, external salts (KCl, MgCl2, or KH2PO4) had minimal effects on the magnitude of light activation of NADP-malate dehydrogenase. In contrast, measurements of chloroplast NADP-malate dehydrogenase activity (after release by osmotic shock) showed a marked dependence on salt concentration. Rates were stimulated approximately 2-fold by both monovalent (optimally 75 millimolar) and divalent (optimally 20 millimolar) salts. It was inferred that the salt-induced increase in net rates of O2 evolution linked to oxaloacetate reduction is due, at least in part, to stimulation of NADP-malate dehydrogenase caused by monovalent cation permeability of the chloroplast inner envelope membrane. 相似文献
3.
Three RNases in Senescent and Nonsenescent Wheat Leaves : Characterization by Activity Staining in Sodium Dodecyl Sulfate-Polyacrylamide Gels 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have described three RNases in wheat leaves (Triticum aestivum L. cv Chinese Spring) and developed assays for measuring each RNase individually in crude leaf extracts. We initially used activity staining in sodium dodecyl sulfate-polyacrylamide gels to characterize RNases in extracts of primary and flag leaves. We thus identified acid RNase (EC 3.1.27.1, here designated RNase WLA), and two apparently novel enzymes, designated RNases WLB and WLC. RNase WLB activity displays a distinctive isozyme pattern, a molecular mass of 26 kilodaltons (major species), a broad pH range with an optimum near neutrality, insensitivity to EDTA, and stimulation by moderate concentrations of KCl and by MgCl2. RNase WLC activity exhibits a molecular mass of 27 kilodaltons, a neutral pH optimum, insensitivity to EDTA, and inhibition by KCl, MgCl2, and tri-(hydroxymethyl)aminomethane. Based on distinctive catalytic properties established in gels, we designed conventional solution assays for selective quantitation of each RNase activity. We used the assays to monitor the individual RNases after gel filtration chromatography and native gel electrophoresis of extracts. In accompanying work, we used the assays to monitor RNases WLA, WLB, and WLC, which are present in senescent and nonsenescent leaves, during the course of leaf senescence. 相似文献
4.
Isolation of dihydroxyacetone phosphate reductase from dunaliella chloroplasts and comparison with isozymes from spinach leaves
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A dihydroxyacetone phosphate (DHAP) reductase has been isolated in 50% yield from Dunaliella tertiolecta by rapid chromatography on diethylaminoethyl cellulose. The activity was located in the chloroplasts. The enzyme was cold labile, but if stored with 2 molar glycerol, most of the activity was restored at 30°C after 20 minutes. The spinach (Spinacia oleracea L.) reductase isoforms were not activated by heat treatment. Whereas the spinach chloroplast DHAP reductase isoform was stimulated by leaf thioredoxin, the enzyme from Dunaliella was stimulated by reduced Escherichia coli thioredoxin. The reductase from Dunaliella was insensitive to surfactants, whereas the higher plant reductases were completely inhibited by traces of detergents. The partially purified, cold-inactivated reductase from Dunaliella was reactivated and stimulated by 25 millimolar Mg2+ or by 250 millimolar salts, such as NaCl or KCl, which inhibited the spinach chloroplast enzyme. Phosphate at 3 to 10 millimolar severely inhibited the algal enzyme, whereas phosphate stimulated the isoform in spinach chloroplasts. Phosphate inhibition of the algal reductase was partially reversed by the addition of NaCl or MgCl2 and totally by both. In the presence of 10 millimolar phosphate, 25 millimolar MgCl2, and 100 millimolar NaCl, reduced thioredoxin causes a further twofold stimulation of the algal enzyme. The Dunaliella reductase utilized either NADH or NADPH with the same pH maximum at about 7.0. The apparent Km (NADH) was 74 micromolar and Km (NADPH) was 81 micromolar. Apparent Vmax was 1100 μmoles DHAP reduced per hour per milligram chlorophyll for NADH, but due to NADH inhibition highest measured values were 350 to 400. The DHAP reductase from spinach chloroplasts exhibited little activity with NADPH above pH 7.0. Thus, the spinach chloroplast enzyme appears to use NADH in vivo, whereas the chloroplast enzyme from Dunaliella or the cytosolic isozyme from spinach may utilize either nucleotide. 相似文献
5.
Bush LP 《Plant physiology》1969,44(3):347-350
Succinyl CoA synthetase from Nicotiana tabacum exhibited a requirement for univalent and divalent cations. Mn2+ replaced Mg2+ in the assay medium and Co2+ and Ca2+ partially replaced Mg2+. Addition of Zn2+ resulted in no enzyme activity. The enzyme was activated by univalent cations K+, Rb+, NH4+, and Na+; Li+ showed little or no activation. Maximum enzyme activity varied significantly with potassium salts of different anions. Greatest activation was obtained with K3PO4 and, respectively, KCl, KNO3, K2SO4 and KF exhibited steadily decreasing enzyme activation. 相似文献
6.
Paul Reznikoff 《The Journal of general physiology》1928,11(3):221-232
I. The Plasmalemma. 1. On the plasmalemma of amebæ CaCl2 antagonizes the toxic action of LiCl better than it does NaCl, and still better than it does KCl. MgCl2 antagonizes the toxic action of NaCl better than it does LiCl and still better than it does KCl. 2. CaCl2 antagonizes the toxic action of LiCl and of KCl better than does MgCl2: MgCl2 antagonizes NaCl better than does CaCl2. II. The Internal Protoplasm. 3. The antagonizing efficiency of CaCl2 and of MgCl2 are highest against the toxic action of KCl on the internal protoplasm, less against that of NaCl, and least against that of LiCl. 4. CaCl2 antagonizes the toxic action of LiCl better than does MgCl2: MgCl2 antagonizes the toxic action of NaCl and of KCl better than does CaCl2. 5. LiCl antagonizes the toxic action of MgCl2 on the internal protoplasm more effectively than do NaCl or KCl, which have an equal antagonizing effect on the MgCl2 action. III. The Nature of Antagonism. 6. When the concentration of an antagonizing salt is increased to a toxic value, it acts synergistically with a toxic salt. 7. No case was found in which a potentially antagonistic salt abolishes the toxic action of a salt unless it is present at the site (surface or interior) of toxic action. 8. Antagonistic actions of the salts used in these experiments are of differing effectiveness on the internal protoplasm and on the surface membrane. 相似文献
7.
Jike Lu Li Deng Rui Zhao Ruisi Zhang Fang Wang Tianwei Tan 《Journal of Molecular Catalysis .B, Enzymatic》2010,62(1):15-18
Candida sp. 99-125 lipase immobilized on textile membrane was pretreated with several methods to improve its activity and methanol tolerance for biodiesel production. Lipase pretreatments with short chain alcohols from n-propyl alcohol to isobutyl alcohol did not have any positive effect on the lipase activity and methanol tolerance. While lipase treated with methanol solutions from 10 to 20% volume concentrations did enhance the enzyme activity and methanol tolerance, and this lipase activation effect did not exist when methanol volume concentration was 40%. 1 mM salt solutions of (NH4)2SO4, CaCl2, KCl, K2SO4 and MgCl2 pretreatments were the useful tools to improve the lipase activity and methanol tolerance. The reason might be that salts could incorporate with the protein molecular to form a more stable molecular to resist conformation change induced by high methanol concentration. The operational stability of pretreated lipase was improved dramatically for biodiesel production during batch reactions. 相似文献
8.
Henry S. Simms 《The Journal of general physiology》1929,12(4):511-528
1.25 per cent gelatin solutions containing enough NaOH to bring them to pH 7.367 (or KOH to pH 7.203) were made up with various concentrations of NaCl, KCl and MgCl2, alone and in mixtures, up to molar ionic strength. The effects of these salts on the pH were observed. MgCl2 and NaCl alone lower the pH of the Na gelatinate or the K gelatinate, in all amounts of these salts. KCl first lowers the pH (up to 0.01 M K+), then raises the pH. Mixtures of NaCl and KCl (up to 0.09 M of the salt whose concentration is varied) raise the pH; then (up to 0.125 M Na+ or K+) lower the pH; and finally (above 0.125 M) behave like KCl alone. Mixtures of MgCl2 and NaCl raise the pH up to 0.10 M Na+, and lower it up to 0.15 M Na+
regardless of the amount of MgCl
2. Higher concentrations of NaCl have little effect, but the pH in this range of NaCl concentration is lowered with increase of MgCl2. Mixtures of MgCl2 and KCl behave as above described (for MgCl2 and NaCl) and the addition of NaCl plus KCl to gelatin containing MgCl2 produces essentially the same effect as the addition of either alone, except that the first two breaks in this curve come at 0.07 M and 0.08 M [Na+ + K+] and there is a third break at 0.12 M. In this pH range the free groups of the dicarboxylic acids and of lysine are essentially all ionized and the prearginine and histidine groups are essentially all non-ionized. The arginine group is about 84 per cent ionized. Hence we are studying a solution with two ionic species in equilibrium, one with the arginine group ionized, and one with it non-ionized. It is shown that the effect of each salt alone depends upon the effect of the cation on the activity of these two species due to combination. The anomalous effects of cation mixtures may be qualitatively accounted for if one or both of these species fail to combine with the cations in a mixture in proportion to the relative combination in solutions of each cation alone. Special precautions were taken to ensure accuracy in the pH measurements. The mother solutions gave identical readings to 0.001 pH and the readings with salts were discarded when not reproducible to 0.003 pH. All doubtful data were discarded. 相似文献
9.
Summary The effects of different concentrations of KCl, K2SO4, MgCl2 and MgSO4 on the growth in length of the first seminal root of wheat, and on the change in fresh and oven-dry weight of the seedling
and its component parts have been studied. The effect of mannitol was also investigated for comparison and to study the osmotic
action.
The effect of salts on root growth was dependent on salt species; all effects were specific to ions and not due to osmotic
activity of solution.
The growth of wheat roots was suppressed by concentrations of salts much lower than those required to suppress germination.
All solutions of KCl from 0.1 to 50 me/l checked the growth of the root; the retardation increased with increase of concentration.
In K2SO4 there was a slight activation of root growth for one day in 0.1 and 0.5 me/l; then the growth was suppressed after that.
In all other concentrations from 1 to 50 me/l the growth was retarded.
In MgCl2 or MgSO4 there was some activation of root elongation in 0.05, 0.1 and 0.5 me/l; but higher concentrations retarded root growth. 相似文献
10.
The K+-dependent p-nitrophenylphosphatase activity catalyzed by purified (Na+ + K+)-ATPase from pig kidney shows substrate inhibition (Ki about 9.5 mM at 2.1 mM Mg2+). Potassium antagonizes and sodium favours this inhibition. In addition, K+ reduces the apparent affinity for substrate activation, whereas p-nitrophenyl phosphate reduces the apparent affinity for K+ activation. In the absence of Mg2+, p-nitrophenyl phosphate, as well as ATP, accelerates the release of Rb+ from the Rb+ occluded unphosphorylated enzyme. With no Mg2+ and with 0.5 mM KCl, trypsin inactivation of (Na+ + K+)-ATPase as a function of time follows a single exponential but is transformed into a double exponential when 1 mM ATP or 5 mM p-nitrophenyl phosphate are also present. In the presence of 3 mM MgCl2, 5 mM p-nitrophenyl phosphate and without KCl the trypsin inactivation pattern is that described for the E1 enzyme form; the addition of 10 mM KCl changes the pattern which, after about 6 min delay, follows a single exponential. These results suggest that (i) the shifting of the enzyme toward the E1 state is the basis for substrate inhibition of the p-nitrophenulphosphatase acitivy of (Na+ + K+)-ATPase, and (ii) the substrate site during phosphatase activity is distinct from the low-affinity ATP site. 相似文献
11.
The intra-chloroplastic distribution of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) between thylakoid membranes and stroma was studied by determining the enzyme activities in the two fractions, obtained by the rapid centrifugation of hypotonically disrupted chloroplast preparations of spinach and pea leaf tissues. The membrane-associated form of RuBisCO was found to increase in proportion to the concentration of MgCl2 in the disrupting medium; with 20 mM MgCl2 approximately 20% of the total RuBisCO of spinach chloroplasts and 10% of that of pea chloroplasts became associated with thylakoid membranes. Once released from membranes in the absence of MgCl2, addition of MgCl2 did not cause reassociation of the enzyme. The inclusion of KCl in the hypotonic disruption buffer also caused the association of RuBisCO with membranes; however, up to 30 mM KCl, only minimal enzyme activities could be detected in the membranes, whereas above 40 mM KCl there was a sharp increase in the membrane-associated form of the enzyme.Higher concentrations of chloroplasts during the hypotonic disruption, as well as addition of purified preparations of RuBisCO to the hypotonic buffer, resulted in an increase of membrane-associated activity. Therefore, the association of the enzyme with thylakoid membranes appears to be dependent on the concentration of RuBisCO. P-glycerate kinase and aldolase also associated to the thylakoid membranes but NADP-linked glyceraldehyde-3-P dehydrogenase did not. The optimal conditions for enzyme association with the thylakoid membranes were examined; maximal association occurred at pH 8.0. The association was temperature-insensitive in the range of 4° to 25° C. RuBisCO associated with the thylakoid membranes could be gradually liberated to the soluble form upon shaking in a Vortex mixer at maximal speed, indicating that the association is loose.Abbreviations DTT
dithiothreitol
- RuBP
ribulose 1,5-bisphosphate
- RuBisCO
ribulose 1,5-bisphosphate carboxylase/oxygenase
- MES
2-(N-morpholino) ethane sulfonic acid 相似文献
12.
《Experimental mycology》1986,10(4):289-293
We have determined the effects of KCl, ZnCl2, and MgCl2 on kinetic parameters of glucose-6-phosphate dehydrogenases from the bacteriaEscherichia coli, Bacillus stearothermophilus, andLeuconostoc mesenteroides, from the fungiAspergillus parasiticus, Alternaria alternata, Aphanomyces astaci, Saccharomyces cerevisiae, andTorula sp., and from the mammalRattus rattus. Each enzyme was stimulated by increasing ionic strength (KCl) and by MgCl2. One bacterial enzyme, fromE. coli, three fungal enzymes, fromA. parasiticus, S. cerevisiae, andTorula sp., and the rat liver enzyme were inhibited by ZnCl2. These data are discussed in light of our previous proposal that Zn2+ inhibition of this enzyme may stimulate versicolorin synthesis byA. parasiticus. 相似文献
13.
By means of micro-dissection and injection Amœba proteus was treated with the chlorides of Na, K, Ca, and Mg alone, in combination, and with variations of pH. I. The Plasmalemma. 1. NaCl weakens and disrupts the surface membrane of the ameba. Tearing the membrane accelerates the disruption which spreads rapidly from the site of the tear. KCl has no disruptive effect on the membrane but renders it adhesive. 2. MgCl2 and CaCl2 have no appreciable effect on the integrity of the surface membrane of the ameba when applied on the outside. No spread of disruption occurs when the membrane is torn in these salts. When these salts are introduced into the ameba they render the pellicle of the involved region rigid. II. The Internal Protoplasm. 3. Injected water either diffuses through the protoplasm or becomes localized in a hyaline blister. Large amounts when rapidly injected produce a "rushing effect". 4. HCl at pH 1.8 solidifies the internal protoplasm and at pH 2.2 causes solidification only after several successive injections. The effect of the subsequent injections may be due to the neutralization of the cell-buffers by the first injection. 5. NaCl and KCl increase the fluidity of the internal protoplasm and induce quiescence. 6. CaCl2 and MgCl2 to a lesser extent solidify the internal protoplasm. With CaCl2 the solidification tends to be localized. With MgCl2 it tends to spread. The injection of CaCl2 accelerates movement in the regions not solidified whereas the injection of MgCl2 induces quiescence. III. Pinching-Off Reaction. 7. A hyaline blister produced by the injection of water may be pinched off. The pinched-off blister is a liquid sphere surrounded by a pellicle. 8. Pinching off always takes place with injections of HCl when the injected region is solidified. 9. The injection of CaCl2 usually results in the pinching off of the portion solidified. The rate of pinching off varies with the concentration of the salt. The injection of MgCl2 does not cause pinching off. IV. Reparability of Torn Surfaces. 10. The repair of a torn surface takes place readily in distilled water. In the different salt solutions, reparability varies specifically with each salt, with the concentration of the salt, and with the extent of the tear. In NaCl and in KCl repair occurs less readily than in water. In MgCl2 repair takes place with great difficulty. In CaCl2 a proper estimate of the process of repair is complicated by the pinching-off phenomenon. However, CaCl2 is the only salt found to increase the mobility of the plasmalemma, and this presumably enhances its reparability. 11. The repair of the surface is probably a function of the internal protoplasm and depends upon an interaction of the protoplasm with the surrounding medium. V. Permeability. 12. NaCl and KCl readily penetrate the ameba from the exterior. CaCl2 and MgCl2 do not. 13. All four salts when injected into an ameba readily diffuse through the internal protoplasm. In the case of CaCl2 the diffusion may be arrested by the pinching-off process. VI. Toxicity. 14. NaCl and KCl are more toxic to the exterior of the cell than to the interior, and the reverse is true for CaCl2 and MgCl2. 15. The relative non-toxicity of injected NaCl to the interior of the ameba is not necessarily due to its diffusion outward from the cell. 16. HCl is much more toxic to the exterior of a cell than to the interior; at pH 5.5 it is toxic to the surface whereas at pH 2.5 it is not toxic to the interior. NaOH to pH 9.8 is not toxic either to the surface or to the interior. VII. Antagonism. 17. The toxic effects of NaCl and of KCl on the exterior of the cell can be antagonized by CaCl2 and this antagonism occurs at the surface. Although the lethal effect of NaCl is thus antagonized, NaCl still penetrates but at a slower rate than if the ameba were immersed in a solution of this salt alone. 18. NaCl and HCl are mutually antagonistic in the interior of the ameba. No antagonism between the salts and HCl was found on the exterior of the ameba. No antagonism between the salts and NaOH was found on the interior or exterior of the ameba. 19. The pinching-off phenomenon can be antagonized by NaCl or by KCl, and the rate of the retardation of the pinching-off process varies with the concentration of the antagonizing salt. 20. The prevention of repair of a torn membrane by toxic solutions of NaCl or KCl can be antagonized by CaCl2. These experiments show directly the marked difference between the interior and the exterior of the cell in their behavior toward the chlorides of Na, K, Ca, and Mg. 相似文献
14.
Krishna Nath Bong-Kwan Phee Suyeong Jeong Sun Yi Lee Yoshio Tateno Suleyman I. Allakhverdiev Choon-Hwan Lee Hong Gil Nam 《Photosynthesis research》2013,117(1-3):547-556
Photosynthetic complexes in the thylakoid membrane of plant leaves primarily function as energy-harvesting machinery during the growth period. However, leaves undergo developmental and functional transitions along aging and, at the senescence stage, these complexes become major sources for nutrients to be remobilized to other organs such as developing seeds. Here, we investigated age-dependent changes in the functions and compositions of photosynthetic complexes during natural leaf senescence in Arabidopsis thaliana. We found that Chl a/b ratios decreased during the natural leaf senescence along with decrease of the total chlorophyll content. The photosynthetic parameters measured by the chlorophyll fluorescence, photochemical efficiency (F v/F m) of photosystem II, non-photochemical quenching, and the electron transfer rate, showed a differential decline in the senescing part of the leaves. The CO2 assimilation rate and the activity of PSI activity measured from whole senescing leaves remained relatively intact until 28 days of leaf age but declined sharply thereafter. Examination of the behaviors of the individual components in the photosynthetic complex showed that the components on the whole are decreased, but again showed differential decline during leaf senescence. Notably, D1, a PSII reaction center protein, was almost not present but PsaA/B, a PSI reaction center protein is still remained at the senescence stage. Taken together, our results indicate that the compositions and structures of the photosynthetic complexes are differentially utilized at different stages of leaf, but the most dramatic change was observed at the senescence stage, possibly to comply with the physiological states of the senescence process. 相似文献
15.
Isolation and Characterization of Two Enzymes Capable of Hydrolyzing Fructose-1,6-Bisphosphatase from the Lichen Peltigera rufescens 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Two enzymes capable of hydrolyzing fructose-1,6-bisphosphate (FBP) have been isolated from the foliose lichen Peltigera rufescens (Weis) Mudd. These enzymes can be separated using Sephadex G-100 and DEAE Sephacel chromatography. One enzyme has a pH optimum of 6.5, and a substrate affinity of 228 micromolar FBP. This enzyme does not require MgCl2 for activity, and is inhibited by AMP. The second enzyme has a pH optimum of 9.0, with no activity below pH 7.5. This enzyme responds sigmoidally to Mg2+, with half-saturation concentration of 2.0 millimolar MgCl2, and demonstrates hyperbolic kinetics for FBP (Km = 39 micromolar). This enzyme is activated by 20 millimolar dithiothreitol, is inhibited by AMP, but is not affected by fructose-2-6-bisphosphate. It is hypothesized that the latter enzyme is involved in the photosynthetic process, while the former enzyme is a nonspecific acid phosphatase. 相似文献
16.
Ethylene and ethane production in response to salinity stress 总被引:1,自引:1,他引:0
Abstract Ethylene and ethane production in mung bean hypocotyl sections were evaluated as possible indicators of stress due to contact with four salts that are common in natural sites. Ethylene production decreased with increasing concentrations of applied NaCl and KCl. When CaCl2 was applied, the ethylene evolution was greater. However, when MgCl2 was applied, ethylene evolution remained high then decreased and at higher salt concentrations again showed an increase. NaCl (up to 0.1 kmol m?1) and KCl (up to 0.5 kmol m?3) caused a concentration-dependent increase in ethane production. The ethane production with CaCl2 was the lowest among the salts tested and only a minute increase was noticed with the increase of concentration from 0.01 to 1 kmol m?3. Ethane production showed a distinct maximum at 0.2 kmol m?3 MgCl2. The introduction of 0.01 kmol m?3 CaCl2, as well as anaerobic conditions obtained by purging vials with N2, eliminated that high ethane production. Respiratory activity of the mung bean hypocotyl sections in MgCl2 concentrations from 0 to 0.5 kmol m?3 was correlated with ethane but not with ethylene production. The ethane/ethylene ratio showed three patterns for the four salts tested. 相似文献
17.
Ai Hasegawa Asami Kurita Shinji Hayashi Takeshi Fukumoto Hamako Sasamoto 《Plant biotechnology reports》2013,7(2):205-209
The effects of sea salts, NaCl, KCl, MgCl2, MgSO4, and CaCl2, on the growth of protoplast cultures of two mangrove species, Sonneratia alba and Avicennia alba, were investigated using 96-well culture plates. Plants of these two species naturally grow at the seaward side of a mangrove forest. Cotyledon protoplasts of S. alba showed halophilic nature to NaCl, KCl, and MgCl2 at low concentrations (10–50 mM) when cultured in Murashige and Skoog’s (MS) medium containing 0.6 M mannitol. CaCl2 at a concentration higher than 25 mM was inhibitory to cell growth. On the other hand, in protoplast culture of A. alba suspension cells, which were induced from cotyledon tissues, in the modified amino acid (mAA) medium containing 1.2 M sorbitol, tolerance to NaCl, MgCl2 and MgSO4 were observed at a wide range of concentrations up to 400 mM. CaCl2 was always inhibitory for cell divisions in A. alba, but stimulatory for spherical enlargement of cells. However, no difference in cell enlargement was observed among other salts. Similarity and difference in reactivity to salts between protoplasts and suspension cells from our previous studies were discussed in relation to the site of salt tolerance or halophilic adaptation within mangrove cells. For protoplast cultures, the site(s) for response of S. alba and A. alba are located in the cytoplasm and/or the cell membrane. 相似文献
18.
Protection of DNA by salts against thermodegradation at temperatures typical for hyperthermophiles 总被引:2,自引:0,他引:2
The effect of physiological concentrations of KCl and MgCl2 on the chemical stability of double-stranded and single-stranded DNA has been studied at temperatures typical for hyperthermophiles.
These two salts protect both double and single-stranded DNA against heat-induced cleavage by inhibiting depurination. High
KCl concentrations also protect DNA cleavage at apurinic sites, while high MgCl2 concentrations stimulate this cleavage. It has been previously proposed that salt protects double-stranded DNA against depurination
by stabilizing the double helix. However, the inhibition of the depurination of single-stranded DNA by KCl and MgCl2 indicates that this effect is more probably due to a direct interaction of salts with purine nucleotides. These results suggest
that the number and nature of heat-induced DNA lesions which have to be repaired might be quite different from one hyperthermophile
to another, depending on their intracellular salt concentration. High salt concentrations might be also useful to protect
DNA in long polymerase chain reaction (PCR) experiments and for long-term preservation.
Received: October 12, 1997 / Accepted: January 29, 1998 相似文献
19.
The activation of the coupling factor-latent ATPase enzyme by tryptic proteolysis may resemble the activation of many proenzymes by limited proteolysis. The beta (53 000 dalton) subunit of solubilized coupling factor-latent ATPase from Mycobacterium phlei was selectively lost in some trypsin-treated samples. Since a concomitant loss of ATPase activity was not observed, the beta subunit may not be essential for ATPase catalytic activity. Treatment of solublized coupling factor with chymotrypsin rapidly produced an A′-type (61 000 dalton) species from the native alpha (64 000 dalton) subunits with partial activation of the ATPase enzyme. Secondary chymotryptic cleavage yielded an A″-type (58 000 dalton) species and a less-active enzyme. Storage of fresh coupling factor samples at ?20°C in the presence of 4 mM MgCl2 with several freeze-thaw cycles resulted in loss of ATPase activity without apparent change in alpha subunit structure. Storage at 4°C in the presence or absence of MgCl2 both decreased ATPase activity and generated A′-type alpha subunit species. Since presence of phenylmethylsulfonyl fluoride prevented these changes, an unknown protease was suspected. The peptide bonds first cleaved by trypsin, chymotrypsin, and the unknown protease are all apparently located within the same small segment of alpha subunit polypeptide chain. 相似文献
20.
Soluble proteins released into the medium of aortic tissues in culture behave as substrates for the enzyme lysyl oxidase. The reaction shows an unusual dependence on the concentration of neutral salts in the assay medium. Practically no enzyme activity was observed in Tris-HCl, 0.005 m, pH 7.6 buffer. However, supplementing the buffer with high concentrations of KCl, KBr, NaCl, and (NH4)2SO4 (in decreasing order of effectiveness) accelerated velocities as much as 10-fold. CaCl2, KSCN, and KI at increasing concentrations became strongly inhibitory. β-Aminopropionitrile, a specific inhibitor of lysyl oxidase, effectively blocked the catalysis in low and high KCl. The salt-stimulated effects on lysyl oxidase activity were not as noticeable when insoluble proteins were used as substrates. Kinetic studies employing double reciprocal plots revealed that high KCl concentrations (2.0 m) raised the maximum velocity of the reaction but did not alter the apparent Km. Thus high salt concentrations did not affect the binding of the soluble substrate to the enzyme. In high salts, however, more radioactive substrate proteins appeared to bind to the enzyme, suggesting that the high salt environment increases the fraction of the total enzyme potentially capable of binding to and catalyzing a reaction with the substrate. 相似文献