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排序方式: 共有825条查询结果,搜索用时 328 毫秒
61.
Jesudason R Sato S Parameswaran H Araujo AD Majumdar A Allen PG Bartolák-Suki E Suki B 《Biophysical journal》2010,99(9):3076-3083
Many fundamental cellular and extracellular processes in the body are mediated by enzymes. At the single molecule level, enzyme activity is influenced by mechanical forces. However, the effects of mechanical forces on the kinetics of enzymatic reactions in complex tissues with intact extracellular matrix (ECM) have not been identified. Here we report that physiologically relevant macroscopic mechanical forces modify enzyme activity at the molecular level in the ECM of the lung parenchyma. Porcine pancreatic elastase (PPE), which binds to and digests elastin, was fluorescently conjugated (f-PPE) and fluorescent recovery after photobleach was used to evaluate the binding kinetics of f-PPE in the alveolar walls of normal mouse lungs. Fluorescent recovery after photobleach indicated that the dissociation rate constant (koff) for f-PPE was significantly larger in stretched than in relaxed alveolar walls with a linear relation between koff and macroscopic strain. Using a network model of the parenchyma, a linear relation was also found between koff and microscopic strain on elastin fibers. Further, the binding pattern of f-PPE suggested that binding sites on elastin unfold with strain. The increased overall reaction rate also resulted in stronger structural breakdown at the level of alveolar walls, as well as accelerated decay of stiffness and decreased failure stress of the ECM at the macroscopic scale. These results suggest an important role for the coupling between mechanical forces and enzyme activity in ECM breakdown and remodeling in development, and during diseases such as pulmonary emphysema or vascular aneurysm. Our findings may also have broader implications because in vivo, enzyme activity in nearly all cellular and extracellular processes takes place in the presence of mechanical forces. 相似文献
62.
Sunil Kumar Battu Michael A. Repka Sindhuri Maddineni Amar G. Chittiboyina Mitchell A. Avery Soumyajit Majumdar 《AAPS PharmSciTech》2010,11(3):1466-1475
The objective of the present research was to evaluate the physicochemical characteristics of berberine chloride and to assess the complexation of drug with 2-hydroxypropyl-β-cyclodextrin (HPβCD), a first step towards solution dosage form development. The parameters such as log P value were determined experimentally and compared with predicted values. The pH-dependent aqueous solubility and stability were investigated following standard protocols at 25°C and 37°C. Drug solubility enhancement was attempted utilizing both surfactants and cyclodextrins (CDs), and the drug/CD complexation was studied employing various techniques such as differential scanning calorimetry, Fourier transform infrared, nuclear magnetic resonance, and scanning electron microscopy. The experimental log P value suggested that the compound is fairly hydrophilic. Berberine chloride was found to be very stable up to 6 months at all pH and temperature conditions tested. Aqueous solubility of the drug was temperature dependent and exhibited highest solubility of 4.05 ± 0.09 mM in phosphate buffer (pH 7.0) at 25°C, demonstrating the effect of buffer salts on drug solubility. Decreased drug solubility was observed with increasing concentrations of ionic surfactants such as sodium lauryl sulfate and cetyl trimethyl ammonium bromide. Phase solubility studies demonstrated the formation of berberine chloride–HPβCD inclusion complex with 1:1 stoichiometry, and the aqueous solubility of the drug improved almost 4.5-fold in the presence of 20% HPβCD. The complexation efficiency values indicated that the drug has at least threefold greater affinity for hydroxypropyl-β-CD compared to randomly methylated-β-CD. The characterization techniques confirmed inclusion complex formation between berberine chloride and HPβCD and demonstrated the feasibility of developing an oral solution dosage form of the drug.KEY WORDS: berberine chloride, complexation, cyclodextrin, solubility, surfactants 相似文献
63.
Jonojit Roy Soumi Naha Madhumita Majumdar Nirmalya Banerjee 《Plant Cell, Tissue and Organ Culture》2007,90(1):31-39
An efficient method of mass propagation of Dendrobium chrysotoxum Lindl. was developed using a shoot-tip culture system. Both direct and callus-mediated formation of protocorm-like bodies
(PLBs) occurred from the basal cut surface of explants. Frequency of callusing was best in the presence of 2 μM thidiazuron
(TDZ) or N6-benzylaminopurine (BAP). The callus exhibited complete hormone autonomy for growth and differentiation of PLBs and was maintained
for 18 months without any exogenous growth regulators, an aspect important for minimising somaclonal variation. However, the
rate of callus growth and PLB formation varied with application of cytokinin and auxin. In addition, the callus exhibited
a differential sensitivity to the exogenous cytokinins. While BAP promoted callus growth and PLB differentiation, TDZ was
inhibitory to callus mediated PLB formation and caused extensive necrosis of callus. Although α-naphthaleneacetic acid (NAA)
had no significant effect on the induction of callus, subsequent growth was best in its presence. Using a 3-month subculture
period, a 69-fold increase in callus weight was achieved with 0.5 μM NAA, while as many as 133 PLBs could be obtained per
100 mg callus in the presence of 1 μM NAA. For direct PLB formation, the optimum cytokinin dosage was dependent upon the type
of cytokinin used. While TDZ was most effective at a concentration of 1 μM (15 PLBs per explant), for similar PLB yield the
application of 8 μM BAP was essential. 相似文献
64.
Ermolenko DN Majumdar ZK Hickerson RP Spiegel PC Clegg RM Noller HF 《Journal of molecular biology》2007,370(3):530-540
Protein synthesis is believed to be a dynamic process, involving structural rearrangements of the ribosome. Cryo-EM reconstructions of certain elongation factor G (EF-G)-containing complexes have led to the proposal that translocation of tRNA and mRNA through the ribosome, from the A to P to E sites, is accompanied by a rotational movement between the two ribosomal subunits. Here, we have used F?rster resonance energy transfer (FRET) to monitor changes in the relative orientation of the ribosomal subunits in different complexes trapped at intermediate stages of translocation in solution. Binding of EF-G to the ribosome in the presence of the non-hydrolyzable GTP analogue GDPNP or GTP plus fusidic acid causes an increase in the efficiency of energy transfer between fluorophores introduced into proteins S11 in the 30 S subunit and L9 in the 50 S subunit, and a decrease in energy transfer between S6 and L9. Similar anti-correlated changes in energy transfer occur upon binding the GTP-requiring release factor RF3. These changes are consistent with the counter-clockwise rotation of the 30 S subunit relative to the 50 S subunit observed in cryo-EM studies. Reaction of ribosomal complexes containing the peptidyl-tRNA analogues N-Ac-Phe-tRNAPhe, N-Ac-Met-tRNAMet or f-Met-tRNAfMet with puromycin, conditions favoring movement of the resulting deacylated tRNAs into the P/E hybrid state, leads to similar changes in FRET. Conversely, treatment of a ribosomal complex containing deacylated and peptidyl-tRNAs bound in the A/P and P/E states, respectively, with EF-G.GTP causes reversal of the FRET changes. The use of FRET has enabled direct observation of intersubunit movement in solution, provides independent evidence that formation of the hybrid state is coupled to rotation of the 30 S subunit and shows that the intersubunit movement is reversed during the second step of translocation. 相似文献
65.
Mazumdar S Bhattacharyya S Ghosh S Majumdar S Ganguly NK 《Molecular and cellular biochemistry》2007,297(1-2):9-19
An immunodominant heat shock protein (Hsp 24) was purified from Vibrio cholerae O139 at 42 degrees C and used as an immunomodulator for studying the gut immune response. T cell clone and T cell line specific for the Hsp 24 were generated from the lymphocytes of lamina propria and intra-epithelial lymphocytes of mice orally infected with V. cholerae O139, respectively. The T cell clone was TCR alphabeta(+), CD4(+) and appeared to play an important role in the functioning of gut B-lymphocytes. The T cell line had heterogenous population of CD8+ and CD4+ cells, most of which were found to be TCR alphabeta(+) and a minor population was TCR gammadelta(+). The lymphokine profile of T cell line showed IFN-gamma to be the most abundant lymphokine followed by IL-2 and IL-4. The possible involvement of alternative pathway of activation for T cell clone was also addressed in this study. The splenocytes showed an up-regulation of their CD2 receptor expression on stimulation with the Hsp-24. The pattern of lymphokines released by splenocytes stimulated with the Hsp-24 showed no particular cell type to be responsible for mounting immune response. Thus, there is involvement of both, mucosal and peripheral arm of the immune system. 相似文献
66.
67.
Loveena Rishi Rohan DhimanManoj Raje Sekhar Majumdar 《Biochimica et Biophysica Acta (BBA)/General Subjects》2007
Constitutive active NF-κB have been shown to protect cutaneous T cell lymphoma (CTCL) cells from apoptosis. In the present study, we have studied the cytotoxic potential of nitric oxide generating compound, sodium nitroprusside (SNP) on CTCL cell line, HuT-78. Treatment of cells with SNP resulted in decrease in mitochondrial membrane potential, cytochrome c release, activation of caspase-3 and poly (ADP ribose) polymerase cleavage. SNP treatment inhibited activation of NF-κB in a concentration dependent manner. SNP increased the expression of IκBα without affecting the phosphorylation of IκBα. Downregulation of NF-κB by SNP decreased p65 nuclear translocation as evident by confocal fluorescence microscopy. Further it was found that SNP treatment caused downregulation of Bcl-2 family member (Bcl-xl) in HuT-78 cells. Thus, we have provided evidence that SNP induces apoptosis in CTCL cell line, HuT-78 by downregulating constitutive NF-κB and thereby Bcl-xl expression. 相似文献
68.
A galactose-specific adhesin was isolated from the fimbriae of an enteroaggregative Escherichia coli (EAEC) strain. The adhesin was found to be a high molecular weight aggregate of the 18-kDa monomer. The dimeric (36 kDa)
and tetrameric (76 kDa) forms appeared in sodium dodecyl sulphate polyacrylamide gel electrophoresis when a higher concentration
of the adhesin was used. The IgGAD (IgG against adhesin) obtained from the immune sera raised in rabbits against purified adhesin could detect all three forms
of the adhesin even from the crude fimbrial preparation. The IgGAD failed to recognize the adhesin in the presence of galactose, thereby suggesting the antibody-binding site and the sugar-binding
site on the adhesin might be same or overlapping. Furthermore, the IgGAD could localize the adhesin exclusively on the fimbriae as observed in immunogold electron microscopy. The aggregative adherence
of the bacteria to HEp-2 cells was reduced to 70% in the presence of the IgGAD. A glycoprotein (34 kDa) present in the membrane fraction of HEp-2 cells interacted with the purified adhesin in a galactose-specific
manner. The IgGAD could recognize the adhesin from the crude fimbrial preparation of 9 out of 10 clinical isolates of EAEC strains but failed
to identify any protein from the crude fimbrial preparation of Salmonella typhimurium (fim +ve as well as fim −ve strain), Vibrio cholerae (WO7) or Escherichia coli DH5α. 相似文献
69.
70.
Improvement of pea biomass and seed productivity by simultaneous increase of phloem and embryo loading with amino acids 下载免费PDF全文
Lizhi Zhang Matthew G. Garneau Rajtilak Majumdar Jan Grant Mechthild Tegeder 《The Plant journal : for cell and molecular biology》2015,81(1):134-146
The development of sink organs such as fruits and seeds strongly depends on the amount of nitrogen that is moved within the phloem from photosynthetic‐active source leaves to the reproductive sinks. In many plant species nitrogen is transported as amino acids. In pea (Pisum sativum L.), source to sink partitioning of amino acids requires at least two active transport events mediated by plasma membrane‐localized proteins, and these are: (i) amino acid phloem loading; and (ii) import of amino acids into the seed cotyledons via epidermal transfer cells. As each of these transport steps might potentially be limiting to efficient nitrogen delivery to the pea embryo, we manipulated both simultaneously. Additional copies of the pea amino acid permease PsAAP1 were introduced into the pea genome and expression of the transporter was targeted to the sieve element‐companion cell complexes of the leaf phloem and to the epidermis of the seed cotyledons. The transgenic pea plants showed increased phloem loading and embryo loading of amino acids resulting in improved long distance transport of nitrogen, sink development and seed protein accumulation. Analyses of root and leaf tissues further revealed that genetic manipulation positively affected root nitrogen uptake, as well as primary source and sink metabolism. Overall, the results suggest that amino acid phloem loading exerts regulatory control over pea biomass production and seed yield, and that import of amino acids into the cotyledons limits seed protein levels. 相似文献