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1.
The effects of chemicals such as metal ions and typical organic enzyme inhibitors on the activity of deglycosylated β-fructofuranosidases ( P -1 and P -2) from Aureobasidium were observed and compared with those of native enzymes. P -1 and P -2 enzymes became sensitive to metal ions, such as Fe2+ , Co2+ , Ni2+ and Al3+ , after deglycosylation. The enzymes were also inhibited by a sulphydryl reagent (monoiodoacetic acid), a peptide-hydrolysing reagent (hydroxylamine) and chelating reagents (sodium citrate, EDTA and sodium azide) after deglycosylation. The importance of deglycosylation for the determination of the true characteristics of the enzymes against chemicals is discussed. 相似文献
2.
M.H. Abd-Alla 《Letters in applied microbiology》1994,19(4):240-243
Of 13 Rhizobium and Bradyrhizobium strains investigated for the production of cellular and extracellular phosphodiesterase and phosphotriesterase, all were found to produce both enzymes. Phosphodiesterase was produced at a much higher level than phosphotriesterase. Rhizobium meliloti TAL 1373 was the most productive. The extracellular enzymes were activated by inclusion in the assay mixture of Ca2+ or Mg2+ . The enzymes were inhibited by Zn2+ but not significantly affected by Cu2+ , Co2+ and Mn2+ . Both hydrolases were inhibited by dithiothreitol but not by thiol-directed inhibitors, suggesting that sulphydryl groups are not directly involved in catalysis. The enzymes have the ability to hydrolyse some organophosphorus compounds, suggesting that Rhizobium and Bradyrhizobium strains play an important role in the degradation of organophosphorus pesticides. 相似文献
3.
Relation of source and sink during grain filling period in wheat and some aspects of its regulation 总被引:1,自引:0,他引:1
H. Herzog 《Physiologia plantarum》1982,56(2):155-160
The effect of Mg2+ , Na+ , K+ , ouabain and pH on ATPase activity of purified membrane fractions enriched in plasmalemma fragments from Hordeum vulgare L. (glycophyte) and Halocnemum strobilaceum L. (halophyte) was studied. Membrane ATPases from both plants were synergistically activated by K+ and Na+ in the presence of Mg2+ . The maximum activity of the enzymes were observed at the ratio Na/K = 2–3. Ouabain (10-4 M) almost completely eliminated the (Na+ + K+ )-stimulated component of the ATPase activity. The Na, K, Mg-ATPase of Hordeum had a single pH optimum (pH 8), but that of the Halocnemum had two optima(pH 6 and 8). It appears that similar enzymes operate in the cells of both plants studied. The higher Na, K, Mg-ATPase activity of the halophyte compared to that of the glycophyte suggests the involvement of the enzyme in the extrusion of Na+ from the cytoplasm of cells of both plants. 相似文献
4.
An improved method for purification of pectate lyases (PLI and PLII) from culture fluids of Pseudomonas fluorescens CY091 and Ps. viridiflava PJ-08-6 by using a phosphocellulose cation exchanger was described. Analysis of purified PLI and PLII by sodium dodecyl sulphate-polyacrylamide and isoelectric focusing gel electrophoresis revealed that both enzymes had been purified to near homogeneity. Optimal Ca2+ concentration required for PLI and PLII activity was determined to be 0·5 mmol l−1 . The Ca2+ requirement could not be replaced by other metal cations such as Mg2+ , Cu2+ , Zn2+ , Fe3+ and Co2+ . Optimal pH for activity was determined to be between 8·5 and 9·0. The K m values for sodium polygalacturonate were 1·28 and 1·11 mg ml−1 for PLI and PLII, respectively. Both PLI and PLII were stable at low temperatures (25°C or below) for at least 1 month. However, at 37°C, the activity decreased 50% in 36 h. Optimal temperatures for activity were estimated to be 46° and 52°C for PLI and PLII, respectively. Thermal stability of both enzymes at elevated temperatures (48°C or higher) increased when CaCl2 or a positively charged molecule such as polylysine was present, but decreased when polygalacturonate or a negatively charged molecule such as heparin was present. PLI and PLII exhibit differential degrees of sensitivity to group-specific inhibitors, including iodoacetic acid and diethylpyrocarbonate. This result suggests that both sulphydryl and imidazole groups are important for the catalytic function of PLI and PLII. 相似文献
5.
Abstract— The hypothesis that the ATPase and phosphatidyhnositol (PI) kinase activities of chromaffin vesicle membranes are catalysed by same enzyme was investigated. The two activities exhibited entirely different responses to variations in Mg2+ or Mn2+ concentrations. In the presence of 1 mM ATP, maximal ATPase activity occurred with 1 mM Mg2+ while maximal PI kinase activity required 100 mM Mg2+ Similar differences were observed with Mn2+ with the exception that maximal ATPase activity occurred with 0.5 mM Mn2+ and maximal PI kinase activity occurred with 5 mM Mn2+ Mn2+ was more effective than Mg2+ in stimulating PI kinase activity at low concentrations, but at optimal concentrations of each, the maximal activity obtained with Mg2+ was 5-fold greater than the maximal activity obtained with Mn2+ The heat stabilities of the two enzymes are vastly different. At 50°C the ATPase activity of the intact membranes was stable for up to 20 min while the t l/2 of PI kinase was less than 2 min. After solubilization in Lubrol PX or at higher temperatures both enzymes were less heat stable, but PI kinase was still inactivated at a much greater rate than the ATPase. The evidence suggests that the ATPase and the PI kinase are different proteins.
The major phosphorylated product was diphosphatidylinositol and once formed, it was stable. Phosphorylation of membrane protein accounted for less than 10% of the total32 P-incorporated into chromaffin vesicles. SDS gel electrophoresis of the solubilized membranes showed the presence of at least 2 major phosphorylated high molecular weight components. 相似文献
The major phosphorylated product was diphosphatidylinositol and once formed, it was stable. Phosphorylation of membrane protein accounted for less than 10% of the total
6.
Calmodulin and calmodulin-mediated processes in plants 总被引:11,自引:3,他引:8
PETER DIETER 《Plant, cell & environment》1984,7(6):371-380
Abstract. The Ca2+ -binding protein calmodulin is found in all plants investigated so far. The comparison of the biochemical and functional properties reveals that it is structurally conserved and functionally preserved throughout the plant and animal kingdom. Among the plant enzymes so far known to be dependent on the Ca2+ -calmodulin complex are NAD kinase(s), Ca2+ -transport ATPase, quinate: NAD+ oxidoreductase, soluble and membrane bound protein kinases, and H+ -transport ATPase. Calmodulin may play also an important role in the regulation of other cellular reactions, such as hormone-mediated processes, secretion of enzymes, and contractile mechanisms. On the basis of the NAD kinase and its regulation by light and Ca2+ -calmodulin, it is suggested that changes in the cellular, free Ca2+ concentration following stimulation may alter the metabolism of a plant cell. According to this suggestion free Ca2+ may act as a second messenger in plants much as it does in animal cells. 相似文献
7.
Purification and characterization of 3-isopropylmalate dehydrogenase from a thermoacidophilic archaebacterium Sulfolobus sp. strain 7 总被引:1,自引:0,他引:1
Emiri Yoda Yoriko Anraku Hiromi Kirino Takayoshi Wakagi Tairo Oshima 《FEMS microbiology letters》1995,131(3):243-247
Abstract 3-Isopropylmalate dehydrogenase was purified (about 2000-fold) to homogeneity for the first time from an archaebacterium, Sulfolobus sp. strain 7. The enzyme showed an apparent molecular mass of about 110 kDa by gel filtration and a single 36-kDa polypeptide band on SDS-PAGE, suggesting tri- or tetrameric structure. The p I value was 6.9. The N-terminal amino acid sequence was similar to enzymes from other sources. The enzyme activity was greatly stimulated by the presence of Mn2+ , Cd2+ , Mg2+ , or Co2+ . In contrast to 3-isopropylmalate dehydrogenase from other sources, monovalent cations such as K2+ and Na2+ were neither essential for activity nor stability of the protein. The enzyme was extraordinarily thermostable. 相似文献
8.
Haruyoshi Konno Susumu Nakashima Toshihiko Maitani Kenji Katoh 《Physiologia plantarum》1999,107(3):287-293
Suspension-cultured carrot ( Daucus carota L. cv. Kintoki) cells were grown in calcium (Ca2+ )-deficient and normal liquid media. Cell growth was limited by the Ca2+ deficiency. Similar amounts of pectic fractions were extracted from the walls of control and Ca2+ -deprived cells, but the fractions from the walls of Ca2+ -deprived cells showed a substantial decrease in galacturonic acid content. However, after 15 days of culture, Ca2+ -deprived cells released galacturonic acid-rich extracellular polysaccharides at twice the rate of control cells. The polysaccharides consisted of a mixture of several polymers containing predominantly arabinose, galactose and galacturonic acid. Ca2+ -deprived cells also secreted three times more extracellular proteins, containing many glycan-hydrolytic enzymes, into the medium than did normal cells. SDS-PAGE analysis revealed several distinct changes in the polypeptide pattern in the medium of control and Ca2+ -deprived cells. Activities of α -galactosidase, β -glucosidase and exo- polygalacturonase increased considerably during Ca2+ deficiency, whereas α - l -arabinofuranosidase and β -galactosidase activities were much reduced. 相似文献
9.
A purified plasmalemma preparation from roots of Plantago major L. ssp. pleiosperma (Pilger) was obtained by the two-phase partitioning method, using 6.5% (w/w) of Dextran T-500 and polyethylene glycol 3350, respectively. The distribution of murker enzymes proved the purity of the plasmalemma fraction. The ATPase activity was characterized by determining its sensitivity to anions, cations and inhibitors. The Mg2+ -dependent ATPase activity peaked at pH 7.25, K+ -stimulation at pH 6.75, and the Cl− -stimulation both at pH 6.75 and 7.5 (all in the presence of 3 m M MgSO4 ). The plasmalemma preparations hydrolyzed preferentially ATP (in the presence of Mg2+ ), although they were less specific for ATP at pH 7.5 than at pH 6.75. The Cl− - stimulated ATPase is probably associated with and located on the plasmalemma. The question if the Cl− -stimulated activity is due to an ATPase distinct from the classical K+ -stimulated ATPase is considered. 相似文献
10.
Response of antioxidative enzymes to nickel and cadmium stress in hyperaccumulator plants of the genus Alyssum 总被引:10,自引:0,他引:10
The term 'phytoremediation' is used to describe the clean-up of heavy metals from contaminated soils by plants. In this study, we examined Alyssum argenteum and Alyssum maritimum for their ability to accumulate Cd2+ . We also exemined Ni2+ accumulation by A. maritimum with comparison with the known Ni-hyperaccumulator A. argenteum , in a hydroponic system. Both species were tolerant to low levels of Cd2+ , and accumulated high quantities under the experimental conditions. Only very low levels of Ni2+ were found in the shoot of A. maritimum , defining it as a non-hyperaccumulator. The role of the antioxidative enzyme system was investigated in relation to Ni2+ and Cd2+ stress. In both species, superoxide dismutase (SOD) activity was elevated at high Cd2+ concentrations, while ascorbate peroxidase (APX) activity remained unchanged and glutathione reductase (GR) activity was reduced. In the presence of Ni2+ , A. maritimum exhibited a typical antioxidative defense mechanism, as evidenced by the elevated activities of all three enzymes tested. A. argenteum exhibited a different enzyme response pattern, with a significant reduction in SOD activity, and elevated APX and GR activities only at the highest Ni2+ concentration. 相似文献
11.
Ca2+ is implicated as a messenger in coupling various environmental stimuli, such as gravity and light, to response. In recent years, it has become evident that Ca2+ plays a central role in all three phases of gravitropism – perception, transduction and response. The root cap, which is known to contain high amounts of Ca2+ and calmoduin, is the primary site of gravity preeception. The possible role of phosphoinositide turnovr and Ca2+ and Ca2+ calmodulin-dependent enzymes such as Ca2+ – ATPase and protein kinases in gravitropsim is discussed. A model is proposed to describe the role of Ca2+ in both normal and light-dependnt gravity response in roots. 相似文献
12.
The activities of 5'-methylthioadenosine (MTA) nucleosidase (EC 2.2.2.28) and 5-methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato ( Lycopersicon esculentum Mill. cv. Rutgers) and cucumber ( Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2- to 4-fold higher in wounded than in intact tissue. Wounded, mature-green tomato tissue treated with specific inhibitors of MTA nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature-green tomato discs were infiltrated with [14 CH3 ] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature-green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+ , while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA nucleosidase and MTR kinase are required for wound-induced ethylene biosynthesis but not for chemical stress-induced ethylene by Cu2+ or Li+ treatments. 相似文献
13.
Glucoamylases produced by Aspergillus niger grown on wheat bran in solid cultures were purified. Four different forms, GA I, GA I', GA II and GA III, were found having apparent molecular weights of 112 000, 104 000, 74 000 and 61 000 Da respectively. The enzymes are glycoproteins with a carbohydrate content of 16%, and optimal activity at 60C and pH 4.4. Activity was strongly inhibited by Hg2+ while Mn2+ and Fe2+ were stimulatory. The Km values for the degradation of starch and maltose were 3.5 and 7.8 mg ml-1 , respectively. 相似文献
14.
ROLE OF MALATE TRANSPORT IN REGULATING METABOLISM IN MITOCHONDRIA ISOLATED FROM RABBIT BRAIN 总被引:2,自引:2,他引:0
Abstract— Partly purified chromaffin granules were incubated in vitro with Ca2+ (with trace amounts of 45 Ca2+ ) in concentrations ranging from 4 μm to 1 mm. After incubation the granules were washed with media containing EDTA and then subjected to density gradient centrifugation (1.3 to 2.0 m-sucrose solutions) in order to characterize the particles which had taken up 45 Ca2+ . By using marker enzymes and various inhibitors of Ca2+ uptake into such cell particles as mitochondria it was established that under the conditions of the experiments chromaffin granules took up Ca2+ from the incubation medium. To characterize this uptake a simplified density gradient procedure was tested and found to be suitable. The uptake of Ca2+ into chromaffin granules was strongly dependent on temperature. It was not activated by ATP. The uptake was linear up to 10 min. At high calcium concentrations (above 200 μm) the rate of uptake levelled off. The uptake at 37°C was 1 nmol Ca2+ /mg protein/min at a Ca2+ concentration of 500 μm. Mg2+ had no influence on Ca2+ uptake, whereas Sr2+ (1 mm) inhibited it. The methods established in this study should prove useful for a further characterization of this Ca2+ uptake into chromaffin granules which is likely to represent a useful model for the Ca2+ uptake occurring in the intact gland. 相似文献
15.
Calcium and plant organelles 总被引:2,自引:0,他引:2
Abstract. The role of intracellular organelles in the regulation of cytosolic Ca2+ levels and whether changes in these levels affect organelle metabolism is considered. We have assessed the biochemical properties of the Ca2+ transporting systems in mitochondrial, chloroplast and microsomal fractions. It is proposed that although all of these organelles can transport Ca2+ to varying extents it would appear that in some tissues at least mitochondria do not play a significant role in the maintenance of cytosolic Ca2+ . The most important Ca2+ transporting systems are probably the ATP dependent Ca2+ extrusion across the plasma membrane and Ca2+ uptake by endoplasmic reticulum, as well as light driven Ca2+ uptake by chloroplasts. Changes in cytoplasmic [Ca2+ ] do appear to regulate the activity of NAD kinase in chloroplasts, the mitochondrial external NADH dehydrogenase and intra-mitochondrial glutamate dehydrogenase, all of which play a key role in plant cell metabolism. Since some of these enzymes are affected by primary stimuli such as light or hormones, it is concluded that Ca2+ may act as a second messenger mediating some of the primary responses. 相似文献
16.
Germinating seedlings of mung bean ( Phaseolus vulgaris L. cv. K-16) were treated with different concentrations of cadmium acetate (10, 50 and 100 μ M ). Cd2+ lowered the chlorophyll and heme levels. The level of lipid peroxides were higher on day 3 than on day 6. However, Cd2+ treatment significantly enhanced the level of lipid peroxides. Similarly, a dose-dependent induction of lipoxygenase (EC 1.13.11.12) activity was observed with Cd2+ treatment. Further, the activities of antioxidant enzymes such as superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were decreased. Our results suggest that lipoxygenase-mediated accumulation of lipid peroxides on the one hand and inhibition of free radical scavenging enzymes like superoxide dismutase and catalase on the other caused a pronounced reduction in the chlorophyll and heme levels of the seedlings. The experiments conducted on the effect of Cd2+ on dark-grown seedlings did not conform with the result of light-grown seedlings. Though chlorophyll and heme levels decreased in a dose-dependent manner, no accumulation of lipid peroxides was observed, suggesting that the inhibition of chlorophyll synthesis by Cd2+ is achieved both by reaction with constituent biosynthetic enzymes as well as peroxide-mediated degradation. 相似文献
17.
Xylanase and β-xylosidase with activity of 6.46 U mg-1 and 0.500 U mg-1 , respectively, were produced extracellularly by Aspergillus ochraceus during growth on pulverized grass in liquid state fermentation, compared to 9.3 U mg-1 and 0.74 U mg-1 when pure xylan was used. The culture filtrate was devoid of any cellulase activity. Xylanolytic enzymes were produced optimally in 144 h of incubation on 1% pulverized grass, pH 6.5. About 8.43% (w/w) sugars were liberated from alkali-treated grass in 6 h by the synergistic effect of xylanolytic enzymes. The half-lives for xylanase and β-xylosidase at 50°C were 210 min and 300 min, respectively, and half-life increased with the increase in protein concentration. Both mono- and divalent cations, especially K+ and Zn2+ , exhibited a profound effect on the rate of enzyme saccharification. 相似文献
18.
† Hitoshi Morikawa †Kazuhiko Fukuda †Shigehisa Kato †Kenjiro Mori Haruhiro Higashida 《Journal of neurochemistry》1995,65(3):1403-1406
Abstract: Voltage-dependent Ca2+ currents were measured in NG108-15 neuroblastoma × glioma hybrid cells transformed to express the rat μ-opioid receptor by the whole-cell configuration of the patch-clamp technique with Ba2+ as charge carrier. A μ-opioid receptor-selective agonist, [ d -Ala2 , N -Me-Phe4 ,Gly5 -ol]enkephalin caused significant inhibition of voltage-dependent Ca2+ currents in μ-receptor-transformed NG108-15 cells but not in nontransfected or vector-transformed control cells. On the other hand, a δ-opioid receptor-selective agonist, [ d -penicillamine2 , d -penicillamine5 ]enkephalin, induced inhibition of voltage-dependent Ca2+ currents in both control and μ-receptor-transformed cells, which is mediated by the δ-opioid receptor expressed endogenously in NG108-15 cells. The inhibition of voltage-dependent Ca2+ currents induced by [ d -Ala2 , N -Me-Phe4 ,Gly5 -ol]enkephalin and [ d -penicillamine2 , d -penicillamine5 ]enkephalin was reduced by pretreatment of the cells with pertussis toxin or ω-conotoxin GVIA. These results indicate that the μ-opioid receptor expressed from cDNA functionally couples with ω-conotoxin-sensitive N-type Ca2+ channels through the action of pertussis toxin-sensitive G proteins in NG108-15 cells. 相似文献
19.
Suresh Bhosale Deepa Kshirsagar Prashant Pawar Tulsiram Yeole Dilip Ranade 《FEMS microbiology letters》1995,127(1-2):151-155
Abstract 5-Aminolevulinic acid dehydratase from the archaebacterium Methanosarcina barken resembles the mammalian and yeast enzymes in its activation by Zn2+ , whereas its activation by K+ resembles the characteristic of bacterial enzymes. This enzyme is activated with Ni2+ which is a component of F430 , a cofactor present mainly in methanogens. The M r of 280000 for the native enzyme and 30 000 ± 2000 for the individual subunit suggest that the enzyme is composed of eight apparently indentical subunits similar to mammalian and yeast enzymes. The enzyme has two pH optima, at 8.5 and 9.4. Higher levels of 5-aminolevulinic acid dehydratase in acetate-grown cells suggest the possibility that regulation and control of this enzyme could be different on various growth substrates. 相似文献
20.
The apparent activity of cytoplasmic fructose bisphosphatase (EC 3.1.3.11) in crude extracts of spinach ( Spinacia oleracea L.) and soybean ( Glycine max [L.] Merr.) leaves was only partially dependent on Mg2+ . At least two major non-chloroplastic fructose bisphosphatases that differed in dependence on Mg2+ were chromatographically resolved from spinach leaves. The Mg2+ -dependent enzyme had an apparent Michaelis constant of 4 μM for fructose-1,6-P2 , was highly specific, and was strongly inhibited by fructose-2,6-P2 . Enzyme activity was inhibited by physiological levels of fructose-6-P.
Both species also contained at least one major enzyme, the activity of which was independent of Mg2+ . These enzymes had pH optima near neutrality, Michaelis constants of 25 to 30 μM for fructose-1,6-P2 , and were inhibited by AMP. Although hexose monophosphates were not metabolized, the enzymes were not specific for fructose-1,6-P2 : phosphate was released from phosphoenolpyruvate and ribulose-1, 5-P2 , and with fructose-1,6-P2 , as substrate, Pi release was about 1.5-fold greater than fructose-6-P production. It is concluded that only the Mg2+ -dependent fructose bisphosphatase, previously characterized, functions in the photosynthetic sucrose formation pathway. Inhibition of the Mg2+ -dependent enzyme by fructose-6-P may be involved in regulation of sucrose formation. 相似文献
Both species also contained at least one major enzyme, the activity of which was independent of Mg