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971.
In this article, carbon nanoparticles (CNPs) were used as a novel fluorescent sensing platform for highly sensitive and selective Hg(2+) detection. To the best of our knowledge, this is the first example of CNPs obtained from candle soot used in this type of sensor. The general concept used in this approach is based on that adsorption of the fluorescently labeled single-stranded DNA (ssDNA) probe by CNP via π-π stacking interactions between DNA bases and CNP leads to substantial dye fluorescence quenching; however, in the presence of Hg(2+), T-Hg(2+)-T induced hairpin structure does not adsorb on CNP and thus retains the dye fluorescence. A detection limit as low as 10nM was achieved. The present CNP-based biosensor for Hg(2+) detection exhibits remarkable specificity against other possible metal ions. Furthermore, superior selectivity performance was observed when Hg(2+) detection was carried out in the presence of a large amount of other interference ions. Finally, in order to evaluate its potential practical application, Hg(2+) detection was conducted with the use of lake water other than pure buffer and it is believed that it holds great promise for real sample analysis upon further development. 相似文献
972.
Qi Wang Cui Min Tingting Yan Hefang Pu Yinqiang Xin Shuangquan Zhang Lan Luo Zhimin Yin 《World journal of microbiology & biotechnology》2011,27(11):2603-2610
l-glutamine (Gln) is an important conditionally necessary amino acid in human body and potential demand in food or medicine
industry is expected. High efficiency of l-Gln production by coupling genetic engineered bacterial glutamine synthetase (GS) with yeast alcoholic fermentation system
has been developed. We report here first the application of small ubiquitin-related modifier (SUMO) fusion technology to the
expression and purification of recombinant Bacillus subtilis GS. In order to obtain GS with high Gln-forming activity, safety and low cost for food and pharmaceutics industry, 0.1% (w/v)
lactose was selected as inducer. The fusion protein was expressed in totally soluble form in E. coli, and expression was verified by SDS–PAGE and western blot analysis. The fusion protein was purified to 90% purity by nickel
nitrilo-triacetic acid (Ni–NTA) resin chromatography with a yield of 625 mg per liter fermentation culture. After the SUMO/GS
fusion protein was cleaved by the SUMO protease, the cleaved sample was reapplied to a Ni–NTA column. Finally, about 121 mg
recombinant GS was obtained from 1 l fermentation culture with no less than 96% purity. The recombinant purified GS showed
great transferase activity (23 U/mg), with 25 U recombinant GS in a 50 ml reaction system, a biosynthesis yield of 27.5 g/l l-Gln was detected by high pressure liquid chromatography (HPLC) or thin-layer chromatography. Thus, the application of SUMO
technology to the expression and purification of GS potentially could be employed for the industrial production of l-Gln. 相似文献
973.
Wang Qi Xin Yinqiang Zhang Feng Feng Zhiyong Fu Jin Luo Lan Yin Zhimin 《World journal of microbiology & biotechnology》2011,27(3):693-700
γ-aminobutyric acid (GABA) is an important bioactive regulator, and its biosynthesis is primarily through the α-decarboxylation of glutamate by glutamate decarboxylase (GAD). The procedures to obtain GABA by bioconvertion with high activity
recombinant Escherichia coli GAD have been seldom understood. In this study, Escherichia coli GAD (gadA) was highly expressed (about 70–75% of total protein) as soluble protein in Escherichia coli BL21(DE3) containing pET28a-gadA, which was induced by 0.4 mM IPTG in LB medium, and maximal GABA-forming activity of the
recombinant GAD was 40 U/mL at a concentration (0.15 mM) of pyridoxal phosphate (PLP) and a concentration (0.6 mM) of Ca2+ at optimal pH of 3.8. The optimal concentration (7.5 mM) of Mn2+ can also improve the activity of recombinant enzyme, but the co-effect of Ca2+ and Mn2+ exhibited antagonism effect when added simultaneously. LB and 0.1% (w/v) lactose were selected as culture medium and inducer,
respectively. The relative activity was markedly higher activated by Ca2+ (174%), Mn2+ (164%) than that by other seven bivalent cations. Finally, the yield of GABA was high of 94 g/L detected by paper chromatography
or HPLC in 1 L reaction system with 30 mL crude GAD (12 U/mL). By entrapping Escherichia coli glutamate decarboxylase into sodium alginate and carrageenan gel beads, the activity of immobilized GAD (IGAD) remained 85%
during the initial five batches and the activity still remained 50% at the tenth batch, these results indicated that the recombinant
Escherichia coli GAD was feasible for the future industrial production of GABA. 相似文献
974.
Objectives: DNA content of diploid H1 (ES) cells (2H1 cells) has been shown to be stable in long‐term culture; however, tetraploid and octaploid H1 (ES) cells (4H1 and 8H1 cells, respectively) were DNA‐unstable. Pentaploid H1 (ES) cells (5H1 cells) established recently have been found to be DNA‐stable; how, then is cell DNA stability determined? To discuss ploidy stability, decaploid H1 (ES) cells (10H1 cells) were established from 5H1 cells and examined for DNA stability. Materials and methods: 5H1 cells were polyploidized using demecolcine (DC) and 10H1 cells were obtained by one‐cell cloning. Results: Number of chromosomes of 10H1 cells was 180 and durations of their G1, S, and G2/M phases were 3, 7 and 6 h respectively. Volume of 10H1 cells was double that of 5H1 cells and morphology of 10H1 cells was flagstone‐like in shape. 10H1 cells exhibited alkaline phosphatase activity and their DNA content decayed in 91 days of culture. 10H1 cells injected into mouse abdomen formed solid tumours that contained several kinds of differentiated cells with lower DNA content, suggesting that 10H1 cells were pluripotent and DNA‐unstable. Loss of DNA stability was explained using a hypothesis concerning DNA structure of polyploid cells as DNA reconstructed through ploidy doubling was arranged in mirror symmetry in a new configuration. Conclusion: In the pentaploid–decaploid transition of H1 cells, cell cycle parameters and pluripotency were retained, but morphology and DNA stability were altered. 相似文献
975.
Jianshe Wang Yingguo Bai Pengjun Shi Huiying Luo Huoqing Huang Jun Yin Bin Yao 《World journal of microbiology & biotechnology》2011,27(2):207-213
A xylanase gene, xynA4-2, was obtained from the genome sequence of thermoacidophilic Alicyclobacillus sp. A4 and expressed in Escherichia coli BL21 (DE3). xynA4-2 encodes a mature protein of 411 residues with a calculated molecular weight of 46.8 kDa. Based on the amino acid sequence
similarities (highest identity of 61%), the enzyme was confined into glycoside hydrolase family 10. The purified recombinant
XynA4-2 exhibited maximum activity at pH 6.2 and 55°C. The enzyme was stable over a broad pH range, retaining more than 90%
of the original activity at pH 5.8–12.0, 37°C for 1 h. The substrate specificity of XynA4-2 was relatively narrow, exhibiting
100, 93, and 35% of the relative activity towards birchwood xylan, oat spelt xylan, and wheat arabinoxylan, respectively.
Supplementation of XynA4-2 to mash caused the reduction of mash filtration rate (5.6%) and viscosity (4.0%). When combined
with the commercial glucanase from Sunson, higher reduction was detected in the filtration rate (12.0%) and viscosity (17.2%).
These favorable properties make XynA4-2 a good candidate in the brewing industry. 相似文献
976.
The kinetics of water hyacinth decomposition using pyrolysis and hydrothermal treatment was compared. With pyrolysis, initial vaporization occurred at 453 K as determined by thermogravimetric analysis, while initial solubilisation occurred at 433 K with subcritical hydrothermal treatment. The “kinetic triplet” was determined for the ranges of 423-483 K (range I) and 473-553 K (range II) using the Coats-Redfern method for both treatments. The calculated activation energies for ranges I and II were 110 and 116 kJ/mol for conventional pyrolysis and 145 and 90 kJ/mol for hydrothermal treatment. The similar activation energies for the two temperature ranges observed for pyrolysis implied that only hemicellulose decomposition occurred. For hydrothermal treatment, both hemicellulose and cellulose decomposition occurred in temperature range II, in which a notable lower activation energy was observed. This implied hydrothermal treatment was more suitable for conversion lignocellulosic biomass under these conditions. 相似文献
977.
Shijia Luo Yanhong He Guogui Ning Jiaqi Zhang Guangying Ma Manzhu Bao 《Trees - Structure and Function》2011,25(6):1063-1071
Dove tree (Davidia involucrate) is a Tertiary relic species endemic to China and is reputed to be a ‘living fossil’ in the plant kingdom. Genetic diversity
and genetic structure of this species were analyzed for its conservation and management, using inter-simple sequence repeat
(ISSR) data obtained from eight populations distributed throughout seven provinces of China. A relatively high level of genetic
diversity, at both population and species levels, was detected using the POPGENE software. Analysis of molecular variance
(AMOVA) revealed a moderate level of among-population variation (i.e., 33.21%). The genetic structure of dove tree was closely
consistent with their isolated topographical distribution region based on the results of the STRUCTURE, POPGENE-UPGMA and
PCA analysis. It is postulated that the relatively high level of genetic diversity has been maintained because of: (a) the
original wild geographical distribution, (b) propagation through outcrossing seeds or root suckers, (c) the longevity of individuals
and (d) the relatively little human disturbance. Genetic drift and restricted gene are important factors affecting genetic
differentiation. There was no significant correlation between geographical distances and a pairwise comparison with genetic
distances, as analyzed by the Mantel test, but the clustering result of genetic diversity was consistent with their isolated
topographical distribution regions. Thus, maintaining the stable special habitats associated with this species is recommended
for the in situ conservation. Furthermore, it is important to develop an effective seed germination system for the maintenance
of an ex situ conservation pool of the germplasm resources. 相似文献
978.
979.
Effective virtual screening relies on our ability to make accurate prediction of protein-ligand binding, which remains a great challenge. In this work, utilizing the molecular-mechanics Poisson-Boltzmann (or Generalized Born) surface area approach, we have evaluated the binding affinity of a set of 156 ligands to seven families of proteins, trypsin β, thrombin α, cyclin-dependent kinase (CDK), cAMP-dependent kinase (PKA), urokinase-type plasminogen activator, β-glucosidase A, and coagulation factor Xa. The effect of protein dielectric constant in the implicit-solvent model on the binding free energy calculation is shown to be important. The statistical correlations between the binding energy calculated from the implicit-solvent approach and experimental free energy are in the range of 0.56-0.79 across all the families. This performance is better than that of typical docking programs especially given that the latter is directly trained using known binding data whereas the molecular mechanics is based on general physical parameters. Estimation of entropic contribution remains the barrier to accurate free energy calculation. We show that the traditional rigid rotor harmonic oscillator approximation is unable to improve the binding free energy prediction. Inclusion of conformational restriction seems to be promising but requires further investigation. On the other hand, our preliminary study suggests that implicit-solvent based alchemical perturbation, which offers explicit sampling of configuration entropy, can be a viable approach to significantly improve the prediction of binding free energy. Overall, the molecular mechanics approach has the potential for medium to high-throughput computational drug discovery. 相似文献
980.
Chi L Fan DD Ma XX Mi Y Luo YE Zhu CH Zhu XL Xue WJ 《Biotechnology and applied biochemistry》2011,58(3):175-184
Production of recombinant human-like collagen (RHLC) by thermoinduction of recombinant Escherichia coli BL 21 during high cell density cultivation was investigated in a 30 L bioreactor. The effects of induction temperature (T), pH, and carbon-to-nitrogen molar ratio of the nutrient medium (C/N) were examined. The optimal thermoinduction protocol for RHLC production was determined by using a model coupling genetic algorithm and artificial neural networks. The optimal operating conditions were as follows: maintenance of induction temperature at 42°C for 3 H and then at 39.4°C until the end, induction pH at 7.03, and C/N at 4.8 (mol/mol). The theoretical maximum concentration of RHLC was 12.5 g/L, whereas the experimental value was 12.1 g/L under the optimal induction conditions. 相似文献