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91.
V. Calderón A. Lázaro R.G. Contreras L. Shoshani C. Flores-Maldonado L. González-Mariscal G. Zampighi M. Cereijido 《The Journal of membrane biology》1998,164(1):59-69
Tight junctions (TJs) are cell-to-cell contacts made of strands, which appear as ridges on P faces and complementary furrows
on E faces on freeze fracture replicas. Evidences and opinions on whether these strands are composed of either membrane-bound
proteins or lipid micelles are somewhat varied. In the present work we alter the lipid composition of Madin-Darby canine kidney
monolayers using a novel approach, while studying (i) their transepithelial electrical resistance, a parameter that depends
on the degree of sealing of the TJs; (ii) the apical-to-basolateral flux of 4 kD fluorescent dextran (JDEX), that reflects the permeability of the intercellular spaces; (iii) the ability of TJs to restrict apical-to-basolateral
diffusion of membrane lipids; and (iv) the pattern of distribution of endogenous and transfected occludin, the sole membrane
protein presently known to form part of the TJs. We show that changing the total composition of phospholipids, sphingolipids,
cholesterol and the content of fatty acids, does not alter TER nor the structure of the strands. Interestingly, enrichment
with linoleic acid increases the JDEX by 631%. The fact that this increase is not reflected in a decrease of TER, suggests that junctional strands do not act as
simple resistive elements but may contain mobile translocating mechanisms.
Received: 7 November 1997/Revised: 20 March 1998 相似文献
92.
Kwang Kim A. Louise Creagh Charles A. Haynes 《Biotechnology and Bioprocess Engineering》1998,3(2):71-77
The strain ofSerratia marcescens QM B1466 produces selectively large amount of chitinolytic enzymes (about 1mg/L medium). Enzymatic hydrolysis of chitin to
N-acetyl-β-D-glucosamine (NAG) was performed with a system consisting of two hydrolases (chitinase and chitobiase) produced
by optimization of a microbial host consuming chitin particles. For the development of Large-scale biological process for
the production of NAG from chitinaceous waste, the selection and optimization of a microbial host, particle size of chitin
and pretreatment of chitin source were investigated. Also, the effect of crab/shrimp chitin sources and initial induction
time using chitin as a sole carbon source on chitinase/chitobiase production and NAG production were examined. Crab-shell
chitin(1.5%) treated by dilute acid and, ball-milled with a nominal diameter less than 250m gave the highest chitinase activity
over a 7 days culture. Crude chitinase/chitobiase solution obtained in a 10 L fed-batch fermentation showed a maximum activities
of 23.6 U/mL and 5.1 U/mL, respectively with a feeding time of 3 hrs, near pH 8.5 at 30°C. 相似文献
93.
94.
An effective chemical pretreatment method for lignocellulosic biomass with substituted imidazoles
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Yuzhi Kang Matthew J. Realff Minjeong Sohn Jay H. Lee Andreas S. Bommarius 《Biotechnology progress》2015,31(1):25-34
Lignocellulosic biomass is the most abundant naturally renewable organic resource for biofuel production. Because of its recalcitrance to enzymatic degradation, pretreatment is a crucial step before hydrolysis of the feedstock. A variety of pretreatment methods have been developed and intensively studied to achieve optimal yield without imposing significant adverse impact on the environment. Herein, we present a novel chemical pretreatment method using substituted heterocycles with low temperature and short residence time requirements. 1‐Methylimidazole (MI) is a precursor to some imidazolium‐based ionic liquids. In this study, its potential utilization as a biomass pretreatment agent is being investigated for the first time. At mild conditions, such as 25°C for 5 min at ambient pressure, a substantial increase in the hydrolysis rate throughout the entire course of conversion for cellulose substrate was obtained. Furthermore, the pretreatment effectiveness of MI on both untreated and steam‐exploded lignocellulosic biomass including loblolly pine, switchgrass, and sugarcane bagasse has been studied and MI was found to be an efficient delignifier. Remarkable rate enhancement was also observed for the non‐woody lignocellulosic substrates after a short period of MI pretreatment at ambient conditions. The mechanism of MI pretreatment is explored through analysis of cellulose physical properties including crystallinity index, degree of polymerization, accessibility, and lignin dissolution quantification. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:25–34, 2015 相似文献
95.
Timo Kanzleiter Michaela Rath Sven W. Görgens Jørgen Jensen Daniel S. Tangen Anders J. Kolnes Kristoffer J. Kolnes Sindre Lee Jürgen Eckel Annette Schürmann Kristin Eckardt 《Biochemical and biophysical research communications》2014
The health-promoting effects of regular exercise are well known, and myokines may mediate some of these effects. The small leucine-rich proteoglycan decorin has been described as a myokine for some time. However, its regulation and impact on skeletal muscle has not been investigated in detail. In this study, we report decorin to be differentially expressed and released in response to muscle contraction using different approaches. Decorin is released from contracting human myotubes, and circulating decorin levels are increased in response to acute resistance exercise in humans. Moreover, decorin expression in skeletal muscle is increased in humans and mice after chronic training. Because decorin directly binds myostatin, a potent inhibitor of muscle growth, we investigated a potential function of decorin in the regulation of skeletal muscle growth. In vivo overexpression of decorin in murine skeletal muscle promoted expression of the pro-myogenic factor Mighty, which is negatively regulated by myostatin. We also found Myod1 and follistatin to be increased in response to decorin overexpression. Moreover, muscle-specific ubiquitin ligases atrogin1 and MuRF1, which are involved in atrophic pathways, were reduced by decorin overexpression. In summary, our findings suggest that decorin secreted from myotubes in response to exercise is involved in the regulation of muscle hypertrophy and hence could play a role in exercise-related restructuring processes of skeletal muscle. 相似文献
96.
Rui Zhao Zhenya Zhang Ruiqin Zhang Miao Li Zhongfang Lei Motoo Utsumi Norio Sugiura 《Bioresource technology》2010,101(3):990-994
Rice straw was treated with a mixed solution of acetic acid and propionic acid to enhance its biodegradability. The effect of acid concentration, pretreatment time, and the ratio of solid to liquid on the delignification performance of rice straw were investigated. It was found that the optimal conditions for hydrolysis were 0.75 mol/L acid concentration, 2 h pretreatment time and 1:20 solid to liquid ratio. Batch methane fermentation of untreated rice straw, pretreated rice straw, and the hydrolysates (the liquid fraction) of pretreatment were conducted at 35 °C for 30 days, and the results indicated that methane production of rice straw can be enhanced by dilute organic acid pretreatment. Moreover, most of the acid in hydrolysates can also be converted into methane gas. 相似文献
97.
Circulating muscle-specific microRNA, miR-206, as a potential diagnostic marker for rhabdomyosarcoma 总被引:1,自引:0,他引:1
Mitsuru Miyachi Hideki Yoshida Ken Kikuchi Tomoko Iehara 《Biochemical and biophysical research communications》2010,400(1):89-93
Presently there is no serum biomarker of rhabdomyosarcoma (RMS). Several studies have shown that profiles of microRNA (miRNA) expression differ among tumor types. Here we evaluated the feasibility of using muscle-specific miRNAs (miR-1, -133a, -133b and -206) as biomarkers of RMS. Expression of muscle-specific miRNAs, especially miR-206, was significantly higher in RMS cell lines than in other tumor cell lines, as well as in RMS tumor specimens. Further, serum levels of muscle-specific miRNAs were significantly higher in patients with RMS tumors than in patients with non-RMS tumors. Normalized serum miR-206 expression level could be used to differentiate between RMS and non-RMS tumors, with sensitivity of 1.0 and specificity of 0.913. These results raise the possibility of using circulating muscle-specific miRNAs, especially miR-206, as landmark biomarkers for RMS. 相似文献
98.
Claudin-16 is involved in the paracellular reabsorption of Mg2+ in the thick ascending limb of Henle. Little is known about the mechanism regulating the tight junctional localization of claudin-16. Here, we examined the effect of Mg2+ deprivation on the distribution and function of claudin-16 using Madin-Darby canine kidney (MDCK) cells expressing FLAG-tagged claudin-16. Mg2+ deprivation inhibited the localization of claudin-16 at tight junctions, but did not affect the localization of other claudins. Re-addition of Mg2+ induced the tight junctional localization of claudin-16, which was inhibited by U0126, a MEK inhibitor. Transepithelial permeability to Mg2+ was also inhibited by U0126. The phosphorylation of ERK was reduced by Mg2+ deprivation, and recovered by re-addition of Mg2+. These results suggest that the MEK/ERK-dependent phosphorylation of claudin-16 affects the tight junctional localization and function of claudin-16. Mg2+ deprivation decreased the phosphothreonine levels of claudin-16. The phosphothreonine levels of T225A and T233A claudin-16 were decreased in the presence of Mg2+ and these mutants were widely distributed in the plasma membrane. Furthermore, TER and transepithelial Mg2+ permeability were decreased in the mutants. We suggest that the tight junctional localization of claudin-16 requires a physiological Mg2+ concentration and the phosphorylation of threonine residues via a MEK/ERK-dependent pathway. 相似文献
99.
目的:观察不同频率迷走神经刺激对蟾蜍离体心脏的心率及心率变异的影响。方法:将蟾蜍心脏和右侧迷走交感干离体后,以不同频率电刺激神经,记录心电图曲线并作心率变异性(HRV)分析。结果:交感神经阻断后,电刺激迷走交感干,心率(HR)显著下降(P0.01),全部正常心动周期的标准差(SDNN)和相邻正常心动周期差值的均方根(RMSSD)显著升高(P0.01),不同频率刺激组之间没有明显差异;与对照组相比,各指标变化较大;给药组0.2Hz时高频(HF)显著升高(P0.01),低频/高频比值(LF/HF)明显降低(P0.05),0.8Hz时HF和LF/HF接近刺激前水平。结论:一定范围内增加刺激频率,迷走神经降低心率的作用增强;没有交感神经调节条件下的迷走神经对心率和心率变异的调节可能存在不同的机制。 相似文献
100.