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排序方式: 共有121条查询结果,搜索用时 31 毫秒
1.
Kyriacos Athanasiou Iordanis Arzimanoglou Colette Piccoli Hiroshi Yamasaki 《Cell biology and toxicology》1987,3(3):251-261
Airborne particulates were collected over a period of twelve months by the use of Hi-Vol samplers in the basin of Athens, Greece. N-Hexane extracts were tested in a battery ofin vitro tests for their ability to induce mutation in bacteria as well as mutation, sister chromatid exchange and morphological transformation in cultured mammalian cells. Positive results were found for mutagenicity withSalmonella strain TA98 in the Ames assay, for sister chromatid exchange induction in CHO cells and for transformation in BALB/c 3T3 cells in culture. They also showed weak non-doserelated induction of ouabain resistance in BALB/c 3T3 cells. The contribution of oxidizing and nitrating agents found in the Athens atmosphere, together with sunlight UV irradiation in the formation of direct acting mutagens and potential carcinogens from ambient polycyclic aromatic hydrocarbons, is suggested.Abbreviations FCS
fetal calf serum
- FPG
fluorescent-plus-Giemsa technique
- ouaR
ouabain resistant
- PAH
polycyclic aromatic hydrocarbon
- SCE
sister chromatid exchange
- TSP
total suspended particulate 相似文献
2.
H Eklund M Ingelman B O S?derberg T Uhlin P Nordlund M Nikkola U Sonnerstam T Joelson K Petratos 《Journal of molecular biology》1992,228(2):596-618
The structure of wild-type bacteriophage T4 glutaredoxin (earlier called thioredoxin) in its oxidized form has been refined in a monoclinic crystal form at 2.0 A resolution to a crystallographic R-factor of 0.209. A mutant T4 glutaredoxin gives orthorhombic crystals of better quality. The structure of this mutant has been solved by molecular replacement methods and refined at 1.45 A to an R-value of 0.175. In this mutant glutaredoxin, the active site residues Val15 and Tyr16 have been substituted by Gly and Pro, respectively, to mimic that of Escherichia coli thioredoxin. The main-chain conformation of the wild-type protein is similar in the two independently determined molecules in the asymmetric unit of the monoclinic crystals. On the other hand, side-chain conformations differ considerably between the two molecules due to heterologous packing interactions in the crystals. The structure of the mutant protein is very similar to the wild-type protein, except at mutated positions and at parts involved in crystal contacts. The active site disulfide bridge between Cys14 and Cys17 is located at the first turn of helix alpha 1. The torsion angles of these residues are similar to those of Escherichia coli thioredoxin. The torsion angle around the S-S bond is smaller than that normally observed for disulfides: 58 degrees, 67 degrees and 67 degrees for wild-type glutaredoxin molecule A and B and mutant glutaredoxin, respectively. Each sulfur atom of the disulfide cysteines in T4 glutaredoxin forms a hydrogen bond to one main-chain nitrogen atom. The active site is shielded from solvent on one side by the beta-carbon atoms of the cysteine residues plus side-chains of residues 7, 9, 21 and 33. From the opposite side, there is a cleft where the sulfur atom of Cys14 is accessible and can be attacked by a nucleophilic thiolate ion in the initial step of the reduction reaction. 相似文献
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This study describes a synthesis method of biodegradable macroporous hydrogels suitable as in situ cross-linkable biomaterials. Macroporous hydrogels were based on poly(propylene fumarate-co-ethylene glycol) and prepared via coupled free radical and pore formation reactions. Cross-linking was initiated by a pair of redox initiators, ammonium persulfate and L-ascorbic acid. Pores were formed by the reaction between L-ascorbic acid and sodium bicarbonate, a basic component, which evolved carbon dioxide. Sol fraction of the hydrogels was varied from 0.06 +/- 0.01 to 0.64 +/- 0.01. A stereological approach was used to analyze the morphological properties of the macroporous hydrogels by relating the morphological properties of thin sections to the original three-dimensional macroporous hydrogel. Prepared macroporous hydrogels had porosities between 0.43 +/- 0.08 and 0.84 +/- 0.02 and surface area densities between 55 +/- 3 and 108 +/- 7 cm(-1). Sodium bicarbonate concentration had the greatest effect on both the porosity and surface area density. The effect of copolymer formulation on the porosity and surface area density was insignificant. From thin sections of the macroporous hydrogels, the profile size distributions were determined as an estimate of the pore size distribution. Two formulations synthesized with varying L-ascorbic acid concentration of 0.05 and 0.1 M had median profile sizes of 50-100 and 150-200 microm, respectively. This novel synthesis method allows for the in situ cross-linking of biodegradable macroporous hydrogels with morpholological properties suitable for consideration as an injectable tissue engineering scaffold. 相似文献
5.
Minimal Requirement for a Lentivirus Vector Based on Human Immunodeficiency Virus Type 1 总被引:8,自引:1,他引:7 下载免费PDF全文
V. Narry Kim Kyriacos Mitrophanous Susan M. Kingsman Alan J. Kingsman 《Journal of virology》1998,72(1):811-816
The use of human immunodeficiency virus vectors for gene therapy is hampered by concern over their safety. This concern might be ameliorated, in part, if the viral accessory genes and proteins could be eliminated from the vector genomes and particles. Here we describe a minimal vector system that is capable of transducing nondividing cells and which does not contain tat, vif, vpr, vpu, and nef. 相似文献
6.
Maria Papadovasilaki Dominik Oberthür Renate Gessmann Iosifina Sarrou Christian Betzel Effie Scoulica Kyriacos Petratos 《Biochemistry and Biophysics Reports》2015
The gene coding for the aminoglycoside adenylyltransferase (aadA6) from a clinical isolate of Pseudomonas aeruginosa was cloned and expressed in Escherichia coli strain BL21(DE3)pLysS. The overexpressed enzyme (AadA6, 281 amino-acid residues) and a carboxy-terminal truncated variant molecule ([1-264]AadA6) were purified to near homogeneity and characterized. Light scattering experiments conducted under low ionic strength supported equilibrium between monomeric and homodimeric arrangements of the enzyme subunits. Circular Dichroism spectropolarimetry indicated a close structural relation to adenylate kinases. Both forms modified covalently the aminoglycosides streptomycin and spectinomycin. The enzyme required at least 5 mM MgCl2 for normal Michaelis–Menten kinetics. Streptomycin exhibited a strong substrate inhibition effect at 1 mM MgCl2. The truncated 17 residues at the C-terminus have little influence on protein folding, whereas they have a positive effect on the enzymic activity and stabilize dimers at high protein concentrations (>100 μM). Homology modelling and docking based on known crystal structures yielded models of the central ternary complex of monomeric AadA6 with ATP and streptomycin or spectinomycin. 相似文献
7.
Gidon Ofek Enda P. Dowling Robert M. Raphael J. Patrick McGarry Kyriacos A. Athanasiou 《Biomechanics and modeling in mechanobiology》2010,9(2):153-162
Articular chondrocytes experience a variety of mechanical stimuli during daily activity. One such stimulus, direct shear,
is known to affect chondrocyte homeostasis and induce catabolic or anabolic pathways. Understanding how single chondrocytes
respond biomechanically and morphologically to various levels of applied shear is an important first step toward elucidating
tissue level responses and disease etiology. To this end, a novel videocapture method was developed in this study to examine
the effect of direct shear on single chondrocytes, applied via the controlled lateral displacement of a shearing probe. Through
this approach, precise force and deformation measurements could be obtained during the shear event, as well as clear pictures
of the initial cell-to-probe contact configuration. To further study the non-uniform shear characteristics of single chondrocytes,
the probe was positioned in three different placement ranges along the cell height. It was observed that the apparent shear
modulus of single chondrocytes decreased as the probe transitioned from being close to the cell base (4.1 ± 1.3 kPa), to the
middle of the cell (2.6 ± 1.1 kPa), and then near its top (1.7 ± 0.8 kPa). In addition, cells experienced the greatest peak
forward displacement (~30% of their initial diameter) when the probe was placed low, near the base. Forward cell movement
during shear, regardless of its magnitude, continued until it reached a plateau at ~35% shear strain for all probe positions,
suggesting that focal adhesions become activated at this shear level to firmly adhere the cell to its substrate. Based on
intracellular staining, the observed height-specific variation in cell shear stiffness and plateau in forward cell movement
appeared to be due to a rearrangement of focal adhesions and actin at higher shear strains. Understanding the fundamental
mechanisms at play during shear of single cells will help elucidate potential treatments for chondrocyte pathology and loading
regimens related to cartilage health and disease. 相似文献
8.
Yongdong Feng Gidon Ofek Jianguo Wen Hong Zhao Kyriacos A. Athanasiou 《Progress in biophysics and molecular biology》2010,103(1):148-156
We observed that BMSCs (bone marrow stromal cells) from myeloma patients (myeloma BMSCs) were significantly stiffer than control BMSCs using a cytocompression device. The stiffness of myeloma BMSCs and control BMSCs was further increased upon priming by myeloma cells. Additionally, myeloma cells became stiffer when primed by myeloma BMSCs. The focal adhesion kinase activity of myeloma cells was increased when cells were on stiffer collagen gels and on myeloma BMSCs. This change in myeloma stiffness is associated with increased colony formation of myeloma cells and FAK activation when co-cultured with stiffer myeloma BMSCs or stiffer collagen. Additionally, stem cells of RPMI8226 cells became stiffer after priming by myeloma BMSCs, with concomitant increases of stem cell colony formation. These results suggest the presence of a mechanotransduction loop between myeloma cells and myeloma BMSCs to increase the stiffness of both types of cells via FAK activation. The increase of stiffness may in turn support the growth of myeloma cells and myeloma stem cells. 相似文献
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