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1.
Production and Purification of Extracellular D-Xylose Isomerase from an Alkaliphilic, Thermophilic Bacillus sp. 总被引:1,自引:0,他引:1 下载免费PDF全文
An alkaliphilic, thermophilic Bacillus sp. (NCIM 59) produced extracellular xylose isomerase at pH 10 and 50°C by using xylose or wheat bran as the carbon source. The distribution of xylose isomerase as a function of growth in comparison with distributions of extra- and intracellular marker enzymes such as xylanase and β-galactosidase revealed that xylose isomerase was truly secreted as an extracellular enzyme and was not released because of sporulation or lysis. The enzyme was purified to homogeneity by ammonium sulfate precipitation followed by gel filtration, preparative polyacrylamide gel electrophoresis, and ion-exchange chromatography. The molecular weight of xylose isomerase was estimated to be 160,000 by gel filtration and 50,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating the presence of three subunits. The enzyme is most active at pH 8.0 and with incubation at 85°C for 20 min. Divalent metal ions Mg2+, Co2+, and Mn2+ were required for maximum activity of the enzyme. The Km values for D-xylose and D-glucose at 80°C and pH 7.5 were 6.66 and 142 mM, respectively, while Kcat values were 2.3 × 102 s-1 and 0.5 × 102 s-1, respectively. 相似文献
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Vasanti Deshpande Mala Rao Sulbha Keskar Chittra Mishra 《Enzyme and microbial technology》1984,6(8):371-374
The endo-1,4-β-d-glucanase [cellulase, 1,4-(1,3:1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] activity of two-day old culture filtrates of Penicillium janthinellum has been enhanced four-fold by incubating with a 10-day old culture filtrate of Penicillium funiculosum grown on the same medium. An inactive protein isolated by fractionation of two-day old culture filtrate of P. janthinellum using preparative isoelectric focusing, showed 30- to 50-fold enhancement of endo-1,4-β-d-glucanase activity. This fraction has been designated the ‘procellulase’ in the present paper. The purity of the procellulase was confirmed by analytical isoelectric focusing and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. It had a molecular weight of 68 000 and an isoelectric point of pH 3.7. 相似文献
4.
Efrem Kentiba Soumitra Mondal D. Mathivanan Mala George 《Chronobiology international》2013,30(12):1742-1747
ABSTRACTThe purpose of this study was to compare chronotype preferences of college students from high- and low-altitude backgrounds living in a tropical setting of Ethiopia. Chronotype (morningness–eveningness) is a preference for a given time of day for physical or mental activities. The present cross-sectional study employed Horne and Osteberg Morningness-Eveningness Questionnaires to evaluate chronotype preferences. The chronotype preference of 264 male college students from varied altitude backgrounds indicated significant differences (p < 0.001). Our findings confirm our hypothesis, of the prevalence of M-types dominant chronotype among college students at low than high altitude. However, we did not confirm our second hypothesis, since students from high-altitude backgrounds were generally I-type dominant chronotype. Similarly, students’ academic performances from low- compared to high-altitudes backgrounds also indicated significant differences (p < 0.003). Better academic performances were seen in students with I-type chronotype orientations from high altitudes. 相似文献
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The entorhinal cortex (EC) provides the predominant excitatory drive to the hippocampal CA1 and subicular neurons in chronic epilepsy. Discerning the mechanisms underlying signal integration within EC neurons is essential for understanding network excitability alterations involving the hippocampus during epilepsy. Twenty-four hours following a single seizure episode when there were no behavioral or electrographic seizures, we found enhanced spontaneous activity still present in the rat EC in vivo and in vitro. The increased excitability was accompanied by a profound reduction in I(h) in EC layer III neurons and a significant decline in HCN1 and HCN2 subunits that encode for h channels. Consequently, dendritic excitability was enhanced, resulting in increased neuronal firing despite hyperpolarized membrane potentials. The loss of I(h) and the increased neuronal excitability persisted for 1 week following seizures. Our results suggest that dendritic I(h) plays an important role in determining the excitability of EC layer III neurons and their associated neural networks. 相似文献
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Chakraborty M Abrams SI Camphausen K Liu K Scott T Coleman CN Hodge JW 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(12):6338-6347
CD8(+) CTL play important roles against malignancy in both active and passive immunotherapy. Nonetheless, the success of antitumor CTL responses may be improved by additional therapeutic modalities. Radiotherapy, which has a long-standing use in treating neoplastic disease, has been found to induce unique biologic alterations in cancer cells affecting Fas gene expression, which, consequently, may influence the overall lytic efficiency of CTL. Here, in a mouse adenocarcinoma cell model, we examined whether exposure of these tumor cells to sublethal doses of irradiation 1) enhances Fas expression, leading to more efficient CTL killing via Fas-dependent mechanisms in vitro; and 2) improves antitumor activity in vivo by adoptive transfer of these Ag-specific CTL. Treatment of carcinoembryonic Ag-expressing MC38 adenocarcinoma cells with irradiation (20 Gy) in vitro enhanced Fas expression at molecular, phenotypic, and functional levels. Furthermore, irradiation sensitized these targets to Ag-specific CTL killing via the Fas/Fas ligand pathway. We examined the effect of localized irradiation of s.c. growing tumors on the efficiency of CTL adoptive immunotherapy. Irradiation caused up-regulation of Fas by these tumor cells in situ, based on immunohistochemistry. Moreover, localized irradiation of the tumor significantly potentiated tumor rejection by these carcinoembryonic Ag-specific CTL. Overall, these results showed for the first time that 1) regulation of the Fas pathway in tumor cells by irradiation plays an important role in their sensitization to Ag-specific CTL; and 2) a combination regimen of tumor-targeted irradiation and CTL promotes more effective antitumor responses in vivo, which may have implications for the combination of immunotherapy and radiation therapy. 相似文献
8.
Percutaneous cryoablation of colorectal liver metastases: potentiated by two consecutive freeze-thaw cycles 总被引:12,自引:0,他引:12
Cryoablation may be beneficial for selected patients with liver tumours. Two freeze-thaw cycles at the same location have been recommended during treatment as this potentiate the effect of ablation in experimental studies. However, single freeze ablations are used by some as double freeze procedures are time-consuming and have been associated with increased risk of complications. Estimation of ice-ball volume is difficult using regularly used monitoring techniques. Magnetic resonance imaging, however, allows excellent and multiplanar visualisation of the frozen region during ablation. We comment on the effect of double freeze cycles in regard to ice-ball volume as estimated from magnetic resonance imaging during percutaneous cryoablation of colorectal liver metastases. The ice-ball volume at the end of the second freeze cycle was median 42% larger than the volume at the end of the first freeze. Double freeze cycles may thus facilitate tumour destruction. 相似文献
9.
Diversity of the native diazotrophs associated with the rhizosphere of pearl millet (P. glaucumn), grown in nutritionally poor soils of semi-arid regions was studied with a view to isolate effective nitrogen fixing and plant growth stimulating bacteria with root associative characteristics. The native population varied from 10(3)-10(4) g(-1) of rhizosphere soil after 40 d growth and belonged to genera Azospirillum, Azotobacter and Klebsiella. Another non-diazotrophic root associative group was Pseudomonas sp., which also produced IAA and enhanced plant growth. Some of these rhizobacteria showed high in vitro acetylene reduction activity along with production of indole acetic acid. Out of 11 selected diazotrophs used as seed inoculants, M10B (Azospirillum sp.), M11E (Azotobacter sp.) and M12D4 (Klebsiella sp.) resulted in significant increase in total root and shoot nitrogen at 45 and 60 days of plant growth under pot culture conditions. 相似文献
10.
In an earlier report on fungal protease (F-prot)-fatty acid biocomposite film formation [Gole et al. Anal. Chem. 2000, 72, 4301], it was observed that the biocatalytic activity of the immobilized enzyme was comparable to that of the free enzyme in solution. However, a somewhat negative aspect of the protocol was the steady loss in activity during reuse and storage of the biocomposite film. In this paper, we address the latter issues and demonstrate successful attempts toward the realization of efficient biocomposite films with enhanced biological activity, temporal stability, and excellent reusability. The improved performance of the F-prot-stearic acid biocomposite is accomplished by preordering the fatty acid film by incorporation of Pb(2+) ions into the lipid matrix prior to enzyme immobilization. The lead cation induces lamellar ordering in the lipid film and thus facilitates diffusion of the F-prot molecules into the lipid matrix and accessibility of the substrate molecules (hemoglobin, Hb) to the entrapped F-prot enzyme molecules. The preordering consequently leads to effective control of the "mass transport" problem and might be responsible for the enhanced biological activity ( approximately 36%) of the enzyme molecules in the biocomposite in comparison with the free enzyme in solution, as well the excellent reusability of the composite film. In addition to biocatalytic activity measurements, the formation and characterization of the F-prot-lead stearate biocomposite films was done by quartz crystal microgravimetry and X-ray diffraction. 相似文献