Biomedical subjects
Publications and source records attributed to L An.
We report on the characterization of nanometer-scale torsional devices based on individual single-walled carbon nanotubes as the spring elements. The axial shear moduli of the nanotubes are obtained through modeling of device reaction to various amounts of applied electrostatic force and are compared to theoretical values.
Mitogen-activated protein kinases (MAPKs) are important signal transducing enzymes that connects diverse receptors/sensors to a wide range of cellular responses in mammals, yeasts and plants. In recent years, a large number of different components of plant MAPK cascades were isolated. Molecular and biochemical studies have revealed that plant MAPKs play important role in the response to a broad variety of biotic and abiotic stresses, including wounding, pathogen infection, temperature, drought, salinity, but also in the signaling of plant hormones and the cell division. This review briefly summaries the recent research results about the cross-talk and complexity of MAP kinase cascades in plant obtained from functional analyses.
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It is generally perceived that biodiversity is better protected from human activities after an area is designated as a protected area. However, we found that this common perception was not true in Wolong Nature Reserve (southwestern China), which was established in 1975 as a "flagship" protected area for the world-renowned endangered giant pandas. Analyses of remote sensing data from pre- and post-establishment periods indicate that the reserve has become more fragmented and less suitable for giant panda habitation. The rate of loss of high-quality habitat after the reserve's establishment was much higher than before the reserve was created, and the fragmentation of high-quality habitat became far more severe. After the creation of the reserve, rates of habitat loss and fragmentation inside the reserve unexpectedly increased to levels that were similar to or higher than those outside the reserve, in contrast to the situation before the reserve was created.
A new chemical shift imaging technique was developed to efficiently obtain separate images for multiple chemical shift peaks from a set of spin-echo acquisitions. Information from localized NMR spectroscopy was used to model the chemical shift spectrum as sharp peaks with known resonance frequencies but unknown amplitudes. Based on this model, a set of spin-echo images with shifted 180 degrees RF pulses were acquired, in which the magnetization vectors of different chemical components were put into different directions. The amplitudes of the chemical shift peaks were obtained by solving nonlinear equations in a region-growing process. Experimental results on an ethanol phantom as well as a subject with silicone breast implants are presented. Magn Reson Med 46:126-130, 2001.
The ginsenoside-beta-glucosidase that hydrolyzes the beta-(1-->2)-glucoside of the ginsenoside Rg3 sugar moiety to ginsenoside Rh2 was isolated from the ginseng root, and the enzyme was purified and characterized. The enzyme was purified to one spot in SDS polyacrylamide gel electrophoresis, and its molecular weight was about 59 kDa. The optimum temperature of the ginsenoside-beta-glucosidase was 60 degrees C, and the optimum pH was 5.0. Ca2+ ion had positive effect on ginsenoside-beta-glucosidase, while Cu2+ had negative effect on it. The ginsenoside-beta-glucosidase may be a special beta-glucosidase that is different from the original exocellulase such as beta-glucosidase (EC 3.2.1.21).
In order to enhance the expression level of human trefoil factor 3 (hTFF3) in Pichia pastoris, we optimized the transformant growth conditions in shake flasks including carbon sources in growth medium, inoculation ratio, methanol concentration, pH rotation speed and inducing time. The transformant could grow on the glucose to OD600 5.0 after 14 hours inoculation. The best inoculation ration of 100 mL growth medium to the induction medium was 1:1. The expression level of dimeric human trefoil factor 3 induction with 1% methanol for 48 hours at pH 6.0, agitation speed 240 r/min could reach 20 mg/L with OD600 15. The protein was expressed in 5-liter fermentor with 2% methanol induction for 32 hours, finally the cell density reached OD600 120. 100 mg/L of recombinant hTFF3 was obtained in the supernatant.
Ulva pertusa Kjellm alkaline phosphatase (EC 3.3.3.1) is a metalloenzyme, the active site of which contains a tight cluster of two zinc ions and one magnesium ion. The kinetic theory described by Tsou of the substrate reaction during irreversible inhibition of enzyme activity has been employed to study the kinetics of the course of inactivation of the enzyme by EDTA. The kinetics of the substrate reaction at different concentrations of the substrate p-nitrophenyl phosphate (PNPP) and inactivator EDTA indicated a complexing mechanism for inactivation by, and substrate competition with, EDTA at the active site. The inactivation kinetics are single phasic, showing that the initial formation of an enzyme-EDTA complex is a relative rapid reaction, following by a slow inactivation step that probably involves a conformational change of the enzyme. The presence of Zn2+ apparently stabilizes an active-site conformation required for enzyme activity.
The human TFF3 (trefoil factor 3) DNA fragment was amplified by polymerase chain reaction (PCR) from human fetal placenta cDNA. The gene was cloned into the Pichia pastoris expression vector pPIC9K containing AOX 1 promoter and alpha-factor leader sequence. Multi-copies insertion transformants were screened on G418 plates. After the induction by 2% methanol for 48 hours, the expression of dimeric hTFF3 came up to 45% of total proteins in medium, as identified by SDS-PAGE and Western blot assay. The recombinant protein was further purified by S-Sepharose, Q-Sepharose ion-exchange chromatography and Sephacryl-S-100 gel filtration chromatography to the 95% purity, as shown by densitometric scanning. The N-terminus and molecular weight of the recombinant hTFF3 was in good agreement with the native hTFF3. The recombinant protein was proved to have good biological activity of preventing rats from the gastric ulcer induced by hydrochloric acid.
This paper introduced a composite method of treating gastrointestinal tract cancer-thermo-chemotherapy. A complete set of intelligentialized real-time measure and control system was well designed. The experiment result showed that this system has a stable performance and good real-time.
In this paper, the results of EPR, VIS and enzyme activity show that alkaline phophatase from calf intrest directly interacted with additional Cu(II). The added Cu(II) enter into A site of active sites of AKP which decrease enzyme activity. With increase of pH value, the decrease in the intensity of the Cu(II) EPR signal and the change of place signal in VIS were observed. These results suggest that Cu(II) migrate in the active center of the enzyme.
In this paper, a simple experimental method for the determination of enthalpy change of coordinating color reaction has been proposed and a relation formula between absorption and temperature has been deduced. Using coordinating color reaction of cobalt(II) thiocyanate in Tween-80 medium, the linear relation of this formula has been validated: r = 0.9957 and delta H = -44.7 kJ.mol-1, which is accordant with the result obtained from Van't Hoff equation.
Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and DNA sequencing were employed to screen the coding region of the alpha-antichymotrypsin (AACT) gene in Han-Chinese population for polymorphism possibly associated with Alzheimer's disease (AD). Consequently, seven polymorphic sites including 25A>G, 39G>A, 370C>T, 662T>G, 892C>T, 923T>C and 1332A>G were detected. Of them, the 25A>G was reported previously and the others are all novel. We subsequently focused on the 25A>G and the 39G>A polymorphism that were of interest to us and conducted an association study of them by another scanning of 246 controls that matched the AD patients. Statistic test showed that both genotype (p=0.0378, Fisher's exact, two tailed) and allele frequency (p=0.0382, Fisher's exact, two tailed) of 39G>A are different between AD patients and the controls. As for 25A>G, lain only the heterozygous genotype A/G associates with AD (p=0.0220, chi(2)), but not the A allele frequency (p=0.1141, chi(2)).
The properties of microsomal membranes in spring wheat leaves (Triticum aestivum L. cv. Ganlong No. 92-005) exposed to (0) control, 8.64 (T1) and 11.2 kJ m(-2) day(-1) (T2) biologically effective UV-B irradiation (UV-B(BE)) were studied under greenhouse conditions. These irradiance levels correspond to a decrease in the stratospheric ozone of approximately 12.5 and 20%, respectively, for a clear solstice day at Lanzhou (36.04 degrees N, 1550 m), China. Compared with controls, the content of malondialdehyde (MDA) increased by 70.8% in T1 and 83.8% in T2 on the 7th day of the radiation, and the IUFA (index of unsaturated fatty acids) decreased, indicating peroxidation of lipid acids. Simultaneously, a drastic decrease of phospholipid content after 21 days and an increase of membrane lipid microviscosity on UV-B irradiation were also found, suggesting a reduction in the fluidity of membrane lipids. Ethylene emission by the microsomal membrane, in the presence of exogenous 1-aminocyclopropane-1-carboxylic acid was higher in the wheat seedlings after 7, 14 and 21 days' irradiation than in the controls. These changes were correlated with a rise in lipoxygenase activity. Membrane-bound enzymes (Ca2+ -ATPase and Mg2+ -ATPase) were promoted by UV radiation in the first 7 days and significantly decreased after 14 and 21 days' treatment in comparison to control. Our results suggest that UV-B radiation may cause changes in structural complexity and function of microsomal membranes in spring wheat leaves.
The immunosuppressive effects of UVB irradiation have been well documented. The production of cytokines by keratinocytes is considered to play a major role in the induction of local as well as systemic immunosuppression. It is thought that partly due to the interaction of locally produced cytokines with antigen-presenting cells (APC) systemic effects, like antigen-specific tolerance, can be induced. In this study we examined the effect of UVB irradiation on cytokine profiles of peripheral APC as well as the functional consequences. Our results indicate that UVB irradiation impairs T(h)1-mediated immune responses in vivo by suppression of the systemic IL-12p70 production. Splenic APC from UVB-exposed mice showed an enhanced production of prostaglandin E(2), IL-1, IL-6 and tumor necrosis factor-alpha after in vitro stimulation. Also, spleen cells from UVB irradiated IL-4(-/-) mice showed increased IL-6 levels. These APC were less efficient in inducing IFN-gamma production by CD4(+) T cells and suppressed IgM production by B cells. We conclude that the altered cytokine profile of peripheral APC can be responsible for the systemic effects of UVB irradiation on the T(h)1/T(h)2 balance as well as on B cell responses.
A new implementation of the minimum spanning tree (MST) phase unwrapping method is presented. The time complexity of the MST method is reduced from O(n2) to O(n log2 n), where n is the number of pixels in the phase map. Typical 256 x 256 phase maps from magnetic resonance imaging can be unwrapped in seconds, compared with tens of minutes with the O(n2) implementation. This makes the pixel-level MST method time efficient and practically attractive. Index Terms-Image processing, magnetic resonance imaging, medical imaging, phase unwrapping.
The effect of changing the amount of external added Co(trp)n and pH values on the interaction of Cu2Zn2 SOD with organic metal compound (Cobalt(II)-Tryptophane) have been studied by means of ICP, VIS and measurement of enzyme activity. It has found that in aqueous solution, there exists a direct interaction of the metal ions of the active center in the metalloenzyme (Cu2Zn2 SOD) with external added Co(Trp)n. As a result, part of the metal ions in metalloenzyme were replaced and the corresponding metalloenzyme derivatives (Co(II)-substituted derivatives of SOD) were produced and the catalytic activity of enzyme were affected. It has also studied the intensity of interactions in different molar ratios (Cobalt(II)-Tryptophane) and pH values and got some results under the effect of corresponding factors.