共查询到20条相似文献,搜索用时 31 毫秒
1.
Padmarajaiah Nagaraja Anantharaman Shivakumar Ashwinee Kumar Shrestha 《Analytical biochemistry》2009,395(2):231-236
A sensitive, selective, and rapid enzymatic method is proposed for the quantification of hydrogen peroxide (H2O2) using 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and 10,11-dihydro-5H-benz(b,f)azepine (DBZ) as chromogenic cosubstrates catalyzed by horseradish peroxidase (HRP) enzyme. MBTH traps free radical released during oxidation of H2O2 by HRP and gets oxidized to electrophilic cation, which couples with DBZ to give an intense blue-colored product with maximum absorbance at 620 nm. The linear response for H2O2 is found between 5 × 10−6 and 45 × 10−6 mol L−1 at pH 4.0 and a temperature of 25 °C. Catalytic efficiency and catalytic power of the commercial peroxidase were found to be 0.415 × 106 M−1 min−1 and 9.81 × 10−4 min−1, respectively. The catalytic constant (kcat) and specificity constant (kcat/Km) at saturated concentration of the cosubstrates were 163.2 min−1 and 4.156 × 106 L mol−1 min−1, respectively. This method can be incorporated into biochemical analysis where H2O2 undergoes catalytic oxidation by oxidase. Its applicability in the biological samples was tested for glucose quantification in human serum. 相似文献
2.
Adam Sikora Jacek Zielonka Marcos Lopez Joy Joseph B. Kalyanaraman 《Free radical biology & medicine》2009,47(10):1401-1407
In this study, we show that boronates, a class of synthetic organic compounds, react rapidly and stoichiometrically with peroxynitrite (ONOO−) to form stable hydroxy derivatives as major products. Using a stopped-flow kinetic technique, we measured the second-order rate constants for the reaction with ONOO−, hypochlorous acid (HOCl), and hydrogen peroxide (H2O2) and found that ONOO− reacts with 4-acetylphenylboronic acid nearly a million times (k = 1.6 × 106 M− 1 s− 1) faster than does H2O2 (k = 2.2 M− 1 s− 1) and over 200 times faster than does HOCl (k = 6.2 × 103 M− 1 s− 1). Nitric oxide and superoxide together, but not alone, oxidized boronates to the same phenolic products. Similar reaction profiles were obtained with other boronates. Results from this study may be helpful in developing a novel class of fluorescent probes for the detection and imaging of ONOO− formed in cellular and cell-free systems. 相似文献
3.
One and a half year-old Ginkgo saplings were grown for 2 years in 7 litre pots with medium fertile soil at ambient air CO2 concentration and at 700 μmol mol−1 CO2 in temperature and humidity-controlled cabinets standing in the field. In the middle of the 2nd season of CO2 enrichment, CO2 exchange and transpiration in response to CO2 concentration was measured with a mini-cuvette system. In addition, the same measurements were conducted in the crown of one 60-year-old tree in the field. Number of leaves/tree was enhanced by elevated CO2 and specific leaf area decreased significantly.CO2 compensation points were reached at 75–84 μmol mol−1 CO2. Gas exchange of Ginkgo saplings reacted more intensively upon CO2 than those of the adult Ginkgo. On an average, stomatal conductance decreased by 30% as CO2 concentration increased from 30 to 1000 μmol mol−1 CO2. Water use efficiency of net photosynthesis was positively correlated with CO2 concentration levels. Saturation of net photosynthesis and lowest level of stomatal conductance was reached by the leaves of Ginkgo saplings at >1000 μmol mol−1 CO2. Acclimation of leaf net CO2 assimilation to the elevated CO2 concentration at growth occurred after 2 years of exposure. Maximum of net CO2 assimilation was 56% higher at ambient air CO2 concentration than at 700 μmol mol−1 CO2. 相似文献
4.
Dan Wang Qiang Li Wangliang Li Jianmin Xing Zhiguo Su 《Enzyme and microbial technology》2009,45(6-7):491-497
Succinate fermentation was investigated in Escherichia coli strains overexpressing cyanobacterium Anabaena sp. 7120 ecaA gene encoding carbonic anhydrase (CA). In strain BL21 (DE3) bearing ecaA, the activity of CA was 21.8 U mg−1 protein, whereas non-detectable CA activity was observed in the control strain. Meanwhile, the activity of phosphoenolpyruvate carboxylase (PEPC) increased from 0.2 U mg−1 protein to 1.13 U mg−1 protein. The recombinant bearing ecaA reached a succinate yield of 0.39 mol mol−1 glucose at the end of the fermentation. It was 2.1-fold higher than that of control strain which was just 0.19 mol mol−1 glucose. EcaA gene was also introduced into E. coli DC1515, which was deficient in glucose phosphotransferase, lactate dehydrogenase and pyruvate:formate lyase. Succinate yield can be further increased to 1.26 mol mol−1 glucose. It could be concluded that the enhancement of the supply of HCO3− in vivo by ecaA overexpression is an effective strategy for the improvement of succinate production in E. coli. 相似文献
5.
Igor Pirozzi Mark A. Booth 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2009,152(4):586-592
This study compared the mass-specific routine metabolic rate (RMR) of similar sized mulloway (Argyrosomus japonicus), a sedentary species, and yellowtail kingfish (Seriola lalandi), a highly active species, acclimated at one of several temperatures ranging from 10–35 °C. Respirometry was carried out in an open-top static system and RMR corrected for seawater–atmosphere O2 exchange using mass-balance equations. For both species RMR increased linearly with increasing temperature (T). RMR for mulloway was 5.78T − 29.0 mg O2 kg− 0.8 h− 1 and for yellowtail kingfish was 12.11T − 39.40 mg O2 kg− 0.8 h− 1. The factorial difference in RMR between mulloway and yellowtail kingfish ranged from 2.8 to 2.2 depending on temperature. The energetic cost of routine activity can be described as a function of temperature for mulloway as 1.93T − 9.68 kJ kg− 0.8 day− 1 and for yellowtail kingfish as 4.04T − 13.14 kJ kg− 0.8 day− 1. Over the full range of temperatures tested Q10 values were approximately 2 for both species while Q10 responses at each temperature increment varied considerably with mulloway and yellowtail kingfish displaying thermosensitivities indicative of each species respective niche habitat. RMR for mulloway was least thermally dependent at 28.5 °C and for yellowtail kingfish at 22.8 °C. Activation energies (Ea) calculated from Arrhenius plots were not significantly different between mulloway (47.6 kJ mol− 1) and yellowtail kingfish (44.1 kJ mol− 1). 相似文献
6.
Galactomannans isolated from legume seed endosperms, including those of commercial interest, have been characterized by multidetection aqueous SEC. Galactomannans derived from seeds of the Faboideae subfamily had substantially higher Mw than those from Caesalpinioideae seeds (Mw,Fab = 2.4–3.1 × 106 g/mol, Mw,Caes. = 0.86–2.1 × 106 g/mol) and within the latter botanical subfamily, an apparent correlation between Mw and the degree of galactose substitution DG was found. The molar mass distributions were unimodal and differed primarily by a scale factor, with distributional widths narrower than a true Flory ‘most-probable distribution’; good fits to Schulz–Zimm model were obtained. Across subfamilies no differences were found in the exponents of [η]–M and Rv–M relationships (0.61 ± 0.02, 0.54 ± 0.01, respectively), the Flory chain stiffness ratio (C∞ = 20 ± 1 (BSF analysis)), or the persistence length (Lp = 5.5 ± 0.2 nm) obtained from SEC fraction data. However, it was found that prefactors in the [η]–M and Rv–M relationships as well as the unperturbed parameter KΘ decrease in proportion to DG and therefore chain density. Generalized relationships incorporating galactose-dependent prefactors were therefore developed to model SEC fraction data of native galactomannans ([η]GM = (1800 ± 200) × Mo−1.61 × M0.61±0.02, Rv,GM = 0.63 ± 0.05 × Mo−0.54 × M0.54±0.01) as well as lower-M fractions obtained by ultrasonication ([η]GM = (730 ± 100) × Mo−1.71 × Mw0.71±0.02, Rv,GM = 0.49 ± 0.05 × Mo−0.57 × Mw0.57±0.01, M ≈ 1 × 105-native). As a consequence of this dependence and the observed patterns in molar mass variation, [η] varies within a narrow range for galactomannans as a whole despite substantial Mw differences. 相似文献
7.
Physicochemical properties and antitumor activities for sulfated derivatives of lentinan 总被引:1,自引:0,他引:1
Five fractions of lentinan, a β-(1→3)-d-glucan bearing β-(1→6)-d-glucopyranosyl branches, were treated with chlorosulfonic acid for 90 min at 60 °C in pyridine medium to synthesize water-soluble sulfated derivatives having the substitution degree of 1.44–1.76. The 13C NMR spectra of the sulfated β-glucans indicated that the C-6 position was preferentially substituted by the sulfate groups. The values of the weight-average molecular weight (Mw), radius of gyration (), and intrinsic viscosity ([η]) of the sulfated lentinan fractions were determined by size-exclusion chromatography with multi-angle laser light scattering (SEC–MALLS) and viscometry in 0.15 M aq NaCl at 25 °C, respectively. The dependence of [η] on Mw for the sulfated lentinan was found to be [η] = 8.93 × 10−3 (mL/g) in 0.15 M aq NaCl (for Mw ranging from 14.6 × 104 to 50.4 × 104). On the basis of the Yamakawa–Fujii–Yoshizaki (YFY) theory, the conformational parameters of the sulfated lentinan were calculated as 950 nm−1 for the molar mass per unit contour length (ML), 4.8 nm for the persistence length (q), and 13.9 for the characteristic ratio (C∞), indicating relatively extended single flexible chains in solution. The sulfated glucan fractions exhibited in vitro antiproliferative activities against sarcoma 180 (S-180) cells, and their inhibition ratios were lower than that of the triple-helix lentinan, but higher than that for the one with single random-coil lentinan chains. 相似文献
8.
Ashok Kumar Patel Vijay Kumar Singh Ravi Prakash Yadav A.J.G. Moir Medicherla V. Jagannadham 《Phytochemistry》2009,70(10):1210-1216
A multi-functional enzyme ICChI with chitinase/lysozyme/exochitinase activity from the latex of Ipomoea carnea subsp. fistulosa was purified to homogeneity using ammonium sulphate precipitation, hydrophobic interaction and size exclusion chromatography. The enzyme is glycosylated (14–15%), has a molecular mass of 34.94 kDa (MALDI–TOF) and an isoelectric point of pH 5.3. The enzyme is stable in pH range 5.0–9.0, 80 °C and the optimal activity is observed at pH 6.0 and 60 °C. Using p-nitrophenyl-N-acetyl-β-d-glucosaminide, the kinetic parameters Km, Vmax, Kcat and specificity constant of the enzyme were calculated as 0.5 mM, 2.5 × 10−8 mol min−1 μg enzyme−1, 29.0 s−1 and 58.0 mM−1 s−1 respectively. The extinction coefficient was estimated as 20.56 M−1 cm−1. The protein contains eight tryptophan, 20 tyrosine and six cysteine residues forming three disulfide bridges. The polyclonal antibodies raised and immunodiffusion suggests that the antigenic determinants of ICChI are unique. The first fifteen N-terminal residues G–E–I–A–I–Y–W–G–Q–N–G–G–E–G–S exhibited considerable similarity to other known chitinases. Owing to these unique properties the reported enzyme would find applications in agricultural, pharmaceutical, biomedical and biotechnological fields. 相似文献
9.
Sandoval A Fraisl P Arias-Barrau E Dirusso CC Singer D Sealls W Black PN 《Archives of biochemistry and biophysics》2008,477(2):363-371
These studies defined the expression patterns of genes involved in fatty acid transport, activation and trafficking using quantitative PCR (qPCR) and established the kinetic constants of fatty acid transport in an effort to define whether vectorial acylation represents a common mechanism in different cell types (3T3-L1 fibroblasts and adipocytes, Caco-2 and HepG2 cells and three endothelial cell lines (b-END3, HAEC, and HMEC)). As expected, fatty acid transport protein (FATP)1 and long-chain acyl CoA synthetase (Acsl)1 were the predominant isoforms expressed in adipocytes consistent with their roles in the transport and activation of exogenous fatty acids destined for storage in the form of triglycerides. In cells involved in fatty acid processing including Caco-2 (intestinal-like) and HepG2 (liver-like), FATP2 was the predominant isoform. The patterns of Acsl expression were distinct between these two cell types with Acsl3 and Acsl5 being predominant in Caco-2 cells and Acsl4 in HepG2 cells. In the endothelial lines, FATP1 and FATP4 were the most highly expressed isoforms; the expression patterns for the different Acsl isoforms were highly variable between the different endothelial cell lines. The transport of the fluorescent long-chain fatty acid C1-BODIPY-C12 in 3T3-L1 fibroblasts and 3T3-L1 adipocytes followed typical Michaelis–Menten kinetics; the apparent efficiency (kcat/KT) of this process increases over 2-fold (2.1 × 106–4.5 × 106 s−1 M−1) upon adipocyte differentiation. The Vmax values for fatty acid transport in Caco-2 and HepG2 cells were essentially the same, yet the efficiency was 55% higher in Caco-2 cells (2.3 × 106 s−1 M−1 versus 1.5 × 106 s−1 M−1). The kinetic parameters for fatty acid transport in three endothelial cell types demonstrated they were the least efficient cell types for this process giving Vmax values that were nearly 4-fold lower than those defined form 3T3-L1 adipocytes, Caco-2 cells and HepG2 cells. The same cells had reduced efficiency for fatty acid transport (ranging from 0.82 × 106 s−1 M−1 to 1.35 × 106 s−1 M−1). 相似文献
10.
Decarboxylation kinetics for the carbonatotris(pyridine)cobalt(III) ion in perchloric acid solutions
The kinetics of the decomposition reactions of the CO(py)3(CO3)(H2O)+ ion have been investigated in aqueous perchloric acid solutions over a range of hydrogen ion concentrations (0.10 to 5.0 M) and at two ionic strengths (I = 1.0 and 5.0 M). At the lower ionic strength, plots of ln (At–A∞ versus time show a nonlinearity that is consistent with that expected for consecutive first-order reactions. The rates of the faster reaction are similar to those reported for the spontaneous reduction of aquopyridine-cobalt(III) cations. At the higher ionic strength, the above noted curvature is not apparent and the decarboxylation kinetics of the title complex may be described by a pseudo-first-order rate constant: kobs = k[H3O+]. At 20°C, k = (1.75−+0.09) s−1 M−1 with activation parameters ofΔH‡ = (97 −+ 4) kJ mol−1 and ΔS‡ = −(54 −+ 32) J deg−1 mol−1. These kinetic parameters are compared with those previously reported for the similar complexes, Co(py)4CO3+ and Co(py)2(CO3)(H2O)2+. 相似文献
11.
Toshiaki Mori Momoko Toyoda Tatsuro Ohtsuka Yoshio Okahata 《Analytical biochemistry》2009,395(2):211-216
A biotinylated mannotriose (Man3-bio) was dispersively immobilized in the matrix of biotinylated lactose (Gal-Glc-bio) on a streptavidin-covered, 27-MHz quartz crystal microbalance (QCM), and binding kinetics of concanavalin A (Con A) to Man3-bio in the Gal-Glc-bio matrix could be obtained from frequency decreases (mass increases) of the QCM. Association constants (Ka) and binding and dissociation rate constants (kon and koff) could be determined separately as the 1:1 and 1:2 bindings of Con A to Man3-bio on the surface. When Man3-bio was immobilized with content of 1 to 5 mol% in the matrix, the 1:1 binding of Con A to Man3-bio was obtained as Ka = (4 ± 1) × 106 M−1, kon = (4 ± 1) × 104 M−1 s−1, and koff = (12 ± 2) × 10–3 s−1. On the contrary, when Man3-bio was immobilized with content of 20 to 100 mol% in the matrix, the 1:2 binding of Con A to Man3-bio was obtained as Ka = (14 ± 2) × 106 M−1, kon = (14 ± 2) × 104 M−1 s−1, and koff = (7 ± 2) × 10–3 s−1. Thus, Ka for the 1:2 binding was 10 times larger than that for the 1:1 binding, with a three times larger binding rate constant (kon) and a three times smaller dissociation rate constant (koff). This is the first example to obtain separate kinetic parameters for the 1:1 and 1:2 bindings of lectins to carbohydrates on the surface. 相似文献
12.
Jasaswini Tripathy Dinesh Kumar Mishra Mithilesh Yadav Kunj Behari 《Carbohydrate polymers》2010,79(1):40-46
An unreported graft copolymer of N,N-dimethylacrylamide (DMA) with chitosan has been synthesized under nitrogen atmosphere using peroxymonosulphate/mandelic acid redox pair. The effect of reaction conditions on grafting parameters i.e. grafting ratio, efficiency, conversion, add on and homopolymer has been studied. Experimental results show that maximum grafting has been obtained at 1.0 g dm−3 concentration of chitosan, 30 × 10−2 mol dm−3 concentration of N,N-dimethylacrylamide and 7.0 × 10−3 mol dm−3 concentration of hydrogen ion. It has also been observed that grafting ratio, add on, conversion and efficiency increase upto 3.2 × 10−3 mol dm−3 of mandelic acid, 12.0 × 10−3 mol dm−3 of potassium peroxymonosulphate, 150 min of time and 40 °C of temperature. Grafted polymer has been characterized by FTIR spectroscopy and thermogravimetric analysis. Water swelling capacity of chitosan-g-N,N-dimethylacrylamide has been determined. It has been observed that the graft copolymer is thermally more stable than parent backbone. 相似文献
13.
Sandeep Kumar Alka Dwevedi Arvind M. Kayastha 《Journal of Molecular Catalysis .B, Enzymatic》2009,58(1-4):138-145
The soybean (Glycine max) urease was immobilized on alginate and chitosan beads and various parameters were optimized and compared. The best immobilization obtained were 77% and 54% for chitosan and alginate, respectively. A 2% chitosan solution (w/v) was used to form beads in 1N KOH. The beads were activated with 1% glutaraldehyde and 0.5 mg protein was immobilized per ml of chitosan gel for optimum results. The activation and coupling time were 6 h and 12 h, respectively. Further, alginate and soluble urease were mixed to form beads and final concentrations of alginate and protein in beads were 3.5% (w/v) and 0.5 mg/5 ml gel. From steady-state kinetics, the optimum temperature for urease was 65 °C (soluble), 75 °C (chitosan) and 80 °C (alginate). The activation energies were found to be 3.68 kcal mol−1, 5.02 kcal mol−1, 6.45 kcal mol−1 for the soluble, chitosan- and alginate-immobilized ureases, respectively. With time-dependent thermal inactivation studies, the immobilized urease showed improved stability at 75 °C and the t1/2 of decay in urease activity was 12 min, 43 min and 58 min for soluble, alginate and chitosan, respectively. The optimum pH of urease was 7, 6.2 and 7.9 for soluble, alginate and chitosan, respectively. A significant change in Km value was noticed for alginate-immobilized urease (5.88 mM), almost twice that of soluble urease (2.70 mM), while chitosan showed little change (3.92 mM). The values of Vmax for alginate-, chitosan-immobilized ureases and soluble urease were 2.82 × 102 μmol NH3 min−1 mg−1 protein, 2.65 × 102 μmol NH3 min−1 mg−1 protein and 2.85 × 102 μmol NH3 min−1 mg−1 protein, respectively. By contrast, reusability studies showed that chitosan–urease beads can be used almost 14 times with only 20% loss in original activity while alginate–urease beads lost 45% of activity after same number of uses. Immobilized urease showed improved stability when stored at 4 °C and t1/2 of urease was found to be 19 days, 80 days and 121 days, respectively for soluble, alginate and chitosan ureases. The immobilized urease was used to estimate the blood urea in clinical samples. The results obtained with the immobilized urease were quite similar to those obtained with the autoanalyzer®. The immobilization studies have a potential role in haemodialysis machines. 相似文献
14.
The kinetics of formation of the complex ion, μ-carbonato-di-μ-hydroxo-bis((1,5-diamino-3-aza-pentane) cobalt(III), from the tri-μ-hydroxo-bis((1,5-diamino-3-aza-pentane(III)cobalt(III)) ion in aqueous buffered carbonate solution have been studied spectrophotometrically at 295 nm over the ranges 20.0θ°C34.8, 8.03pH9.44, 5 mM [CO32−35 mM and at an ionic strength of 0.1 M (LiClO4). On the basis of the kinetic results a mechanism, involving rapid cleavage of an hydroxo bridge followed by carbon dioxide uptake with subsequent bridge formation, has been proposed. At 25 °C, the rate of the carbon dioxide uptake is 0.58 M−1 s−1 with ΔH≠ = (13.2±0.7) kcal mol−1 and ΔS≠ = (−15.1 ± 0.7) cal deg−1 mol−1. The results are composed with those obtained for several mononuclear cobalt(III) and one dinuclear cobalt(III) complexes. 相似文献
15.
An influence of methane concentration on the methanotrophic activity of a model landfill cover 总被引:3,自引:0,他引:3
Evaluation of kinetic parameters of methane oxidation under various conditions, on the basis of an analysis of the literature and the authors’ own laboratory research, is presented. Variation in methanotrophic activity in the profile of a simulated landfill cover was observed. The greatest activity was found at a depth of 60 cm. A low affinity (1/KM) and high potential activity (Vmax) were observed. Vmax values ranged from 0.11 × 10−3 to 0.86 × 10−3 units. The values of KM ranged from 0.6 to 2.9% of CH4 (v/v). 相似文献
16.
Net ecosystem exchange of CO2 (NEE) was measured during 2005 using the eddy covariance (EC) technique over a reed (Phragmites australis (Cav.) Trin. ex Steud.) wetland in Northeast China (121°54′E, 41°08′N). Diurnal NEE patterns varied markedly among months. Outside the growing season, NEE lacked a diurnal pattern and it fluctuated above zero with an average value of 0.07 mg CO2 m−2 s−1 resulting from soil microbial activity. During the growing season, NEE showed a distinct V-like diel course, and the mean daily NEE was −7.48 ± 2.74 g CO2 m−2 day−1, ranging from −13.58 g CO2 m−2 day−1 (July) to −0.10 g CO2 m−2 day−1 (October). An annual cycle was also apparent, with CO2 uptake increasing rapidly in May, peaking in July, and decreasing from August. Monthly cumulative NEE ranged from −115 ± 24 g C m−2 month−1 (the reed wetland was a CO2 sink) in July to 75 ± 16 g C m−2 month−1 (CO2 source) in November. The annual CO2 balance suggests a net uptake of −65 ± 14 g C m−2 year−1, mainly due to the gains in June and July. Cumulative CO2 emission during the non-growing season was 327 g C m−2, much greater than the absolute value of the annual CO2 balance, which proves the importance of the wintertime CO2 efflux at the study site. The ratio of ecosystem respiration (Reco) to gross primary productivity (GPP) for this reed ecosystem was 0.95, indicating that 95% of plant assimilation was consumed by the reed plant or supported the activities of heterotrophs in the soil. Daytime NEE values during the growing season were closely related to photosynthetically active radiation (PAR) (r2 > 0.63, p < 0.01). Both maximum ecosystem photosynthesis rate (Amax) and apparent quantum yield (α) were season-dependent, and reached their peak values in July (1.28 ± 0.11 mg CO2 m−2 s−1, 0.098 ± 0.027 μmol CO2 μmol−1 photon, respectively), corresponding to the observed maximum NEE in July. Ecosystem respiration (Reco) relied on temperature and soil water content, and the mean value of Q10 was about 2.4 with monthly variation ranging from 1.8 to 4.1 during 2005. Annual methane emission from this reed ecosystem was estimated to be about 3 g C m−2 year−1, and about 5% of the net carbon fixed by the reed wetland was released to the atmosphere as CH4. 相似文献
17.
Chitosan (Ch) was chemically modified with ethylenesulfide (Es) under solvent-free conditions to give (ChEs), displaying a high content of thiol groups due to opening of the three member cyclic reagent. Elemental analysis showed a decrease in nitrogen content. This result indicated the incorporation of two ethylenesulfide molecules for each unit of the polymeric structure of the precursor biopolymer. Infrared spectroscopy, thermogravimetry, and 13C NMR in the solid state demonstrated the effectiveness of the reaction, with signals at 30 ppm for ChEs due to the change in the methylene group environment. Divalent metal uptake by chemically modified biopolymer gave the order Cu > Ni > Co > Zn, reflecting the corresponding acidity of these cations in bonding to the sulfur and the basic nitrogen atoms available on the pendant chains. The equilibrium data were fitted to Freundlich, Temkin, and Langmuir models. The maximum monolayer adsorption capacity for the cations was found to be 1.54 ± 0.02, 1.25 ± 0.03, 1.13 ± 0.01, and 0.83 ± 0.03 mmol g−1, respectively. The Langmuir model best explained the cation–sulfur bond interactions at the solid–liquid interface. The thermodynamics for these interactions gave exothermic enthalpic values of −43.02 ± 0.03, −28.72 ± 0.02, −26.27 ± 0.04, and −17.32 ± 0.02 kJ mol−1, respectively. The spontaneity of the systems is given by negative Gibbs free energies of −31.2 ± 0.1, −32.7 ± 0.1, −31.7 ± 0.1, and −32.2 ± 0.1 kJ mol−1, respectively, in spite of the unfavorable negative entropic values of −39 ± 1, −13 ± 1, −18 ± 1, and −49 ± 1 J K−1 mol−1 due to solvent ordering in the course of complexation. This newly synthesized biopolymer is presented as a chemically useful material for cation removal from aqueous solution. 相似文献
18.
Yoshiyuki Tanaka Toshihiro Miyajima Katsumasa Yamada Masakazu Hori Natsuki Hasegawa Yu Umezawa Isao Koike 《Aquatic Botany》2008,89(3):331-336
The seasonal variability of specific growth rate and the carbon stable isotope ratio (δ13C) of leaf blades (δ13Cleaf) of a temperate seagrass, Zostera marina (within 10 days old) were measured simultaneously, together with the δ13C of dissolved inorganic carbon (δ13CDIC) at three sites in the semi-closed Akkeshi estuary system, northeastern Japan, in June, September, and November 2004. The δ13Cleaf ranged from −16.2 to −6.3‰ and decreased from summer to winter. The simultaneous measurement of the δ13Cleaf, growth rate, and morphological parameters (mean leaf length and width, mean number of leaves per shoot, and sheath length) of the seagrass and δ13CDIC in the surrounding water allowed us to compare directly the δ13Cleaf and specific growth rate of seagrass. The difference in the δ13C of seagrass leaves relative to the source DIC (Δδ13Cleaf − DIC) was the least negative (−11 to −7‰) in June at all three sites and became more negative (−17 to −8‰) as the specific growth rate decreased. This positive correlation between Δδ13Cleaf − DIC and specific growth rate can be used to diagnose the growth of seagrasses. Δδ13Cleaf − DIC changed by −1.7 ± 0.2‰ when the leaf specific growth rate decreased by 1% d−1. 相似文献
19.
Thomas L. Emmons Karl J. Mathis Mary E. Shuck Beverly A. Reitz Daniel F. Curran Mark C. Walker Joseph W. Leone Jacqueline E. Day Michael J. Bienkowski H. David Fischer Alfredo G. Tomasselli 《Protein expression and purification》2009,65(2):133-139
Soluble guanylate cyclase (sGC) has been purified from 100 L cell culture infected by baculovirus using the newer and highly effective titerless infected-cells preservation and scale-up (TIPS) method. Successive passage of the enzyme through DEAE, Ni2+-NTA, and POROS Q columns obtained approximately 100 mg of protein. The sGC obtained by this procedure was already about 90% pure and suitable for various studies which include high throughput screening (HTS) and hit follow-up. However, in order to obtain enzyme of greater homogeneity and purity for crystallographic and high precision spectroscopic and kinetic studies of sGC with select stimulators, the sGC solution after the POROS Q step was further purified by GTP-agarose affinity chromatography. This additional step led to the generation of 26 mg of enzyme that was about 99% pure. This highly pure and active enzyme exhibited a Mr = 144,933 by static light scattering supportive of a dimeric structure. It migrated as a two-band protein, each of equal intensity, on SDS–PAGE corresponding to the α (Mr 77,000) and β (Mr 70,000) sGC subunits. It showed an A430/A280 = 1.01, indicating one heme per heterodimer, and a maximum of the Soret band at 430 nm indicative of a penta-coordinated ferrous heme with a histidine as the axial ligand. The Soret band shifted to 398 nm in the presence of an NO donor as expected for the formation of a penta-coordinated nitrosyl-heme complex. Non-stimulated sGC had kcat/Km = 1.7 × 10−3 s−1 μM−1 that increased to 5.8 × 10−1 s−1 μM−1 upon stimulation with an NO donor which represents a 340-fold increase due to stimulation. The novel combination of using the TIPS method for co-expression of a heterodimeric heme-containing enzyme, along with the application of a reproducible ligand affinity purification method, has enabled us to obtain recombinant human sGC of both the quality and quantity needed to study structure–function relationships. 相似文献
20.
In vitro effects of arsenic in human peripheral lymphocytes (HPL) at three different doses – 3.6×10−4, 1.4×10−3 and 0.72×10−3 μM for 24 h before harvesting on sister chromatid exchanges (SCE), Cell cycle proliferative index/replicative index (CCPI/RI), %M1, %M2 and %M3, population doubling time (PDT) and average generation time (AGT) were examined. Andrographis paniculata (commonly referred to as ‘kalmegh’) has been used for centuries in traditional Indian and Chinese herbal medicine as a safe, natural folk remedy for assorted health concerns. In the present study, kalmegh (0.01 μg/7 ml culture media) was used along with the highest dose of arsenic; the results showed that arsenic induced increase in these genotoxic endpoints were fairly diminished by kalmegh. In addition, mutagenic in vitro effect of ethyl methanesulphonate (EMS) was used as a positive control in this study. It is thus concluded from this study that Andrographis has a protective role in arsenic toxicity. 相似文献