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21.
Fatemeh Moradian Khosro Khajeh Hossein Naderi-Manesh Majid Sadeghizadeh 《Applied biochemistry and biotechnology》2009,159(1):33-45
Bacillus sp. HR-08 screened from soil samples of Iran, is capable of producing proteolytic enzymes. 16S rDNA analysis showed that
this strain is closely related to Bacillus subtilis, Bacillus licheniformis, Bacillus pumilus, Bacillus mojavensis, and Bacillus atrophaeus. The zymogram analysis of the crude extract revealed the presence of five extracellular proteases. One of the proteases was
purified in three steps procedure involving ammonium sulfate precipitation, DEAE-Sepharose ionic exchange and Sephacryl S-200
gel filtration chromatography. The molecular mass of the enzyme on SDS-PAGE was estimated to be 29 kDa. The protease exhibited
maximum activity at pH 10.0 and 60 °C and was inhibited by PMSF but it was not affected by cysteine inhibitors, suggesting
that the enzyme is a serine alkaline protease. Irreversible thermoinactivation of enzyme was examined at 50, 60, and 70 °C
in the presence of 10 mM CaCl2. Results showed that the protease activity retains more than 80% and 50% of its initial activity after incubation for 30 min
at 60 and 70 °C, respectively. This enzyme had good stability in the presence of H2O2, nonionic surfactant, and local detergents and its activity was enhanced in the presence of 20% of dimethyl sulfoxide (DMSO),
dimethyl formamide (DMF) and isopropanol. The enzyme retained more than 90% of its initial activity after pre-incubation 1 h
at room temperature in the presence of 20% of these solvents. Also, activation can be seen for the enzyme at high concentration
(50%, v/v) of DMF and DMSO. 相似文献
22.
Marzieh Ghollasi Khosro Khajeh Hossein Naderi-Manesh Atiyeh Ghasemi 《Applied biochemistry and biotechnology》2010,162(2):444-459
Successful industrial use of amylases requires that they are sufficiently stable and active at application conditions, e.g.,
at high temperature in starch-liquefaction process. In the present study, site-directed mutagenesis was used to enhance the
thermal stability and calcium independency of a mesophilic α-amylase from Bacillus megaterium WHO. Mutations (A53S and H58I) were designed at the calcium-binding site based on the sequence alignment. Kinetic and thermostability
parameters of the mutants were analyzed and compared with that of the wild type. In the presence of calcium, the affinity
of the enzymes (wild type and mutants) toward starch was increased. In comparison to the wild type, calcium ion had more effect
on the catalytic efficiency, k
cat/K
m, and half-life (at 60 °C) of A53S mutant. In A53S, the dependence of half-life on calcium concentration showed that the enhanced
calcium binding is likely to be responsible for the increased stability. In contrast, calcium-independent mutant (H58I) possessed
high thermostability. In addition, thermodynamic parameters of amylolytic reaction exhibited an increase in the activation
energy and the entropy of the system. Kinetics of irreversible thermal inactivation suggests that the activation energy increased
by 1.4-fold in the most stable variant. 相似文献
23.
Khosro Shahbazi Nathan Albin Oscar P. Bruno Jan S. Hesthaven 《Journal of computational physics》2011,230(24):8779-8796
We introduce a multi-domain Fourier-continuation/WENO hybrid method (FC–WENO) that enables high-order and non-oscillatory solution of systems of nonlinear conservation laws, and which enjoys essentially dispersionless, spectral character away from discontinuities, as well as mild CFL constraints (comparable to those of finite difference methods). The hybrid scheme employs the expensive, shock-capturing WENO method in small regions containing discontinuities and the efficient FC method in the rest of the computational domain, yielding a highly effective overall scheme for applications with a mix of discontinuities and complex smooth structures. The smooth and discontinuous solution regions are distinguished using the multi-resolution procedure of Harten [J. Comput. Phys. 115 (1994) 319–338]. We consider WENO schemes of formal orders five and nine and a FC method of order five. The accuracy, stability and efficiency of the new hybrid method for conservation laws is investigated for problems with both smooth and non-smooth solutions. In the latter case, we solve the Euler equations for gas dynamics for the standard test case of a Mach three shock wave interacting with an entropy wave, as well as a shock wave (with Mach 1.25, three or six) interacting with a very small entropy wave and evaluate the efficiency of the hybrid FC–WENO method as compared to a purely WENO-based approach as well as alternative hybrid based techniques. We demonstrate considerable computational advantages of the new FC-based method, suggesting a potential of an order of magnitude acceleration over alternatives when extended to fully three-dimensional problems. 相似文献
24.
Farangis Ataei Saman Hosseinkhani Khosro Khajeh 《Photochemistry and photobiology》2009,85(5):1162-1167
Firefly luciferase is a 62 kDa protein that produces a flash of light on the oxidation of luciferin in the presence of ATP, Oxygen and Mg2+ . Luciferase has a broad range of applications for analytical purposes and in vivo imaging for nanosystem biology studies. However, the enzyme is highly susceptible to proteolytic degradation that reduces its half-life. Rate of proteolytic digestion between two members of luciferase family ( Photinus pyralis and Lampyris turkestanicus ) is compared. Proteolytic sensitivity of L. turkestanicus luciferase was found to be more than P. pyralis luciferase, due to higher rate of hydrolysis under identical conditions. Both luciferases showed more sensitivity to chymotrypsin than trypsin with different digestion pattern. Digestion of P. pyralis by trypsin produced some fragments which were found to be more resistant to further degradation, whereas in L. turkestanicus initial fragments subdigested by trypsin, like chymotrypsin effect on both luciferases. Furthermore, both luciferases become increasingly labile to proteolysis as the temperature increases. The rate of inactivation and the rate of degradation between luciferases were different in a specific time of incubation. Appearance of similar bands for both luciferases confirmed exposure of specific regions, in spite of structural differences. 相似文献
25.
Zandi K Ramedani E Mohammadi K Tajbakhsh S Deilami I Rastian Z Fouladvand M Yousefi F Farshadpour F 《Natural product communications》2010,5(12):1935-1938
Antiviral drug resistance is one of the most common problems in medicine, and, therefore, finding new antiviral agents, especially from natural resources, seems to be necessary. This study was designed to assay the antiviral activity of curcumin and its new derivatives like gallium-curcumin and Cu-curcumin on replication of HSV-1 in cell culture. The research was performed as an in vitro study in which the antiviral activity of different concentrations of three substances including curcumin, Gallium-curcumin and Cu-curcumin were tested on HSV-1. The cytotoxicity of the tested compounds was also evaluated on the Vero cell line. The CC50 values for curcumin, gallium-curcumin and Cu-curcumin were 484.2 microg/mL, 255.8 microg/mL and 326.6 microg/mL, respectively, and the respective IC50 values 33.0 microg/mL, 13.9 microg/mL and 23.1 microg/mL. The calculated SI values were 14.6, 18.4 and 14.1, respectively. The results showed that curcumin and its new derivatives have remarkable antiviral effects on HSV-1 in cell culture. 相似文献
26.
New 2-substituted pyrazolo[5,1-b][1,3]oxazoles are synthesized through the Sonogashira coupling reaction of 2-iodomethyl-6-methylpyrazolo[5,1-b][1,3]oxazole with terminal alkynes in the presence of a palladium catalyst. This process is carried out in the absence of any copper salt, and provides an eco-friendly and efficient method for the synthesis of the products in water in good-to-high yields. Some of the compounds synthesized were screened for their in vitro anti-oxidant activity using the DPPH (2,2-diphenyl-2-picrylhydrazyl) assays. 相似文献
27.
Substitution reactions of a Cl− ligand in [SnCl2(tpp)] (tpp=5,10,15,20‐tetraphenyl‐21H,23H‐porphinato(2−)) by five organic bases i.e., butylamine (BuNH2), sec‐butylamine (sBuNH2), tert‐butylamine (tBuNH2), dibutylamine (Bu2NH), and tributylamine (Bu3N), as entering nucleophile in dimethylformamide at I=0.1M (NaNO3) and 30–55° were studied. The second‐order rate constants for the substitution of a Cl− ligand were found to be (36.86±1.14)⋅10−3, (32.91±0.79)⋅10−3, (22.21±0.58)⋅10−3, (19.09±0.66)⋅10−3, and (1.36±0.08)⋅10−3 M −1s−1 at 40° for BuNH2, tBuNH2, sBuNH2, Bu2NH, and Bu3N, respectively. In a temperature‐dependence study, the activation parameters ΔH≠ and ΔS≠ for the reaction of [SnCl2(tpp)] with the organic bases were determined as 38.61±4.79 kJ mol−1 and −150.40±15.46 J K−1mol−1 for BuNH2, 40.95±4.79 kJ mol−1 and −143.75±15.46 J K−1mol−1 for tBuNH2, 30.88±2.43 kJ mol−1 and −179.00±7.82 J K−1mol−1 for sBuNH2, 26.56±2.97 kJ mol−1 and −194.05±9.39 J K−1mol−1 for Bu2NH, and 39.37±2.25 kJ mol−1 and −174.68±7.07 J K−1 mol−1 for Bu3N. From the linear rate dependence on the concentration of the bases, the span of k2 values, and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the ligand substitution. 相似文献
28.
In this work, we show that the transmission moiré pattern is two-dimensional autocorrelation of transmission function (2D-ACTF) of two superimposed linear gratings that make a small angle with each other. In this approach, the properties of moiré fringes vs. the relative displacement of the gratings are formulated. By measuring 2D-ACTF of two similar gratings, we evaluate the modulation transfer function (MTF) of the gratings’ generating system. This work is the generalized form of our previous works. The implied MTF measurement method is easier and faster than our previous methods. 相似文献
29.
In this paper, the feasibility of using explosion synthesized diamond nanoparticles with an average particle size (APS) of 3–5 nm with a concentration of 1 % by weight for improving lubrication and friction in elastohydrodynamic lubrication (EHL) was investigated. Owing to the orders of magnitude increase in the viscosity of the lubricant in the EHL contact zone, diamond nanoparticles in the lubricant polish the surfaces at the nanoscale which decreases the composite roughness of contacting surfaces. The reduced composite roughness results in an increased film thickness ratio which yields lower friction. In the numerical analysis, governing equations of lubricant flow in the full elastohydrodynamic lubrication were solved, and the shear stress distribution over the fluid film was calculated. Using an abrasion model and the shear stress distribution profile, the material removal by the nanofluid containing nanoparticles and the resultant surface roughness were determined. The numerical analysis showed that in full EHL regime, the nanolubricant can reduce the composite roughness of moving surfaces. Experimental results from prior studies which exhibited surface polishing by such nanolubricants in boundary, mixed, and full elastohydrodynamic lubrication were used for comparison to the numerical model. 相似文献
30.
Khosro Sayevand J. Tenreiro Machado Iman Masti 《Mathematical Methods in the Applied Sciences》2020,43(17):9928-9947
In recent years, random functional or stochastic equations have been reported in a large class of problems. In many cases, an exact analytical solution of such equations is not available and, therefore, is of great importance to obtain their numerical approximation. This study presents a numerical technique based on Bernstein operational matrices for a family of stochastic fractional integro-differential equations (SFIDE) by means of the trapezoidal rule. A relevant feature of this method is the conversion of the SFIDE into a linear system of algebraic equations that can be analyzed by numerical methods. An upper error bound, the convergence, and error analysis of the scheme are investigated. Three examples illustrate the accuracy and performance of the technique. 相似文献