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Query: HUMANGGP:008114 (TEM)
 20,717 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Scanning and transmission electron microscopy (SEM and TEM) revealed unique structures and development of the venomous spicules of tussock moth caterpillars of the genus Euproctis: (1) Flower-like structure at the distal end and a longitudinal minute depression on the proximal subapical wall of these spicules were observed by SEM. This depression was revealed to be a small hole by TEM. (2) During molting, observed were cytoplasmic processes of several trichogen cells penetrating the cytoplasm of a tormogen cell to form the spicules with the holes at their subapical portions. A papilla was formed by a tormogen and several epidermal cells. (3) After the molting, the cytoplasmic process in a spicule disappeared and the spicule cavity was replaced by electron-dense materials secreted apparently from the trichogen cell. (4) It was considered that the electron-dense materials were the main toxic or precursory substances in the Euproctis spicules.
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PMID:Studies on the venomous spicules and spines of moth caterpillars. I. Fine structure and development of the venomous spicules of the Euproctis caterpillars. 73 32

This investigation examined the tissue response and interfacial bonding between bone and hard-tissue replacement (HTR) using scanning (SEM) and transmission (TEM) electron microscopy. Twenty adult male Sprague-Dawley rats were anesthetized and a hole (1.0 mm deep by 2.0 mm wide) was drilled in the calvarium. Subsequently, HTR was implanted and the wound closed. The implants and surrounding tissues were removed at 7, 14, 28, and 56 days and prepared for examination by SEM or TEM. Scanning electron microscopic analysis revealed a typical inflammatory response that subsided by day 14. At that time, a fine layer of collagen fibrils (fibrous envelope) was observed covering the polymeric surface. Energy dispersive x-ray analysis (EDXA) showed no sign of mineralization. Ultrastructural analysis demonstrated that the fibrous envelope was bilaminar; it consisted of a relatively undifferentiated cellular layer adjacent to the polymer and an outer fibrous region. Scanning electron microscopic analysis of 28-day implants showed that osteoblasts had migrated onto the outer surface of the fibrous envelope and that calcification had been initiated as judged by EDXA. Electron microscopic examination confirmed previous observations of an undifferentiated cellular layer along the interfacial boundary, but also showed both macrophages and foreign-body giant cells. At 56 days, bone was observed to contact and cover the fibrous envelope surrounding the polymeric bead; however, EDXA showed that the fibrous envelope remained noncalcified. Transmission electron microscopic analysis revealed that the inner cellular layer was beginning to mature, as indicated by the presence of numerous cellular organelles. This maturation was accompanied by an increased incidence of macrophages as well as foreign-body giant cells. Within the time constraints of the experimental design, it is apparent that a bilaminar layer of cells and fibers remains between the HTR and the bone. Additional studies will be necessary, over extended time periods, to determine whether the bilaminar layer remains a constant feature between the HTR and the surrounding bone or whether this region is gradually supplanted by the ingrowing bone.
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PMID:The ultrastructural architecture of the tissue/hard-tissue replacement interface. 154 93

A procedure is described for staining large numbers of thin sections on support films for use with one-hole grids. The film is picked up, carried and protected using easily made plastic blocks. Loop-tipped forceps are then used to transfer tissue ribbons from the knife boat to the support film. A large number of tissue sections can then be stained and washed simultaneously in a modified Pyrex dish without damaging the film. After staining, the slot in the one-hole grid is centered over the tissue ribbon, and the grid is attached to the film. The method is suitable for serial reconstruction and the unobstructed viewing of large thin sections in the TEM.
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PMID:Method for staining and washing thin sections on support films. 616 34

The crystal structure of a phosphonate complex of the class A TEM-1 beta-lactamase has been determined to a resolution of 2.0 A. The phosphonate appears stoichiometrically at the active site, bound covalently to Ser70Ogamma, with one phosphonyl oxygen in the oxyanion hole. Although the overall structure is very similar to that of the native enzyme (rms difference 0.37 A for all heavy atoms), changes have occurred in the position of active site functional groups. The active site is also not in the conformation observed in the complex of another class A beta-lactamase, that of Staphylococcus aureus PC1, with the same phosphonate [Chen, C. C. H., et al. (1993) J. Mol. Biol. 234,165-178]. Both phosphonate structures, however, can be seen to represent models of acylation transition-states since in each the deacylating water molecule appears firmly bound to the Glu166 carboxylate group. The major difference between the structures lies in the positioning of Lys73Nzeta and Ser130Ogamma. In the S. aureus structure, the closest interaction of these functional groups is between Lys73Nzeta and Ser70Ogamma (2.8 A), while in the TEM-1 structure it is between Ser130Ogamma and the second phosphonyl oxygen of the bound inhibitor (2.8 A). The former structure therefore may resemble a transition state for formation of the tetrahedral species in acylation by nucleophilic attack on the substrate, where Lys73Nzeta presumably catalyzes the reaction as a general base. The TEM-1 structure can then be seen as an analogue of the transition state for breakdown of the tetrahedral species, where Ser130Ogamma is acting as a general acid, assisting the departure of the leaving group. The class A beta-lactamase crystal structures now available lead to a self-consistent proposal for a mechanism of catalysis by these enzymes.
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PMID:Crystal structure of an acylation transition-state analog of the TEM-1 beta-lactamase. Mechanistic implications for class A beta-lactamases. 948 12

The kinetic parameters of three IRT (Inhibitor-Resistant-TEM-derived-) beta-lactamases (IRT-5, IRT-6 and IRT-I69) were determined for substrates and the beta-lactamase inhibitors: clavulanic acid, sulbactam and tazobactam, and compared with those of TEM-1 beta-lactamase. The catalytic behaviour of the beta-lactamases towards substrates and inhibitors was correlated with the properties of the amino acid at position ABL69. The three IRT beta-lactamases contain at that position a residue Ile, Leu and Val, amino acids whose side-chain are branched. Molecular modelling shows that the methyl groups of Ile-69 (C gamma 2) and Val-69 (C gamma 1) produced steric constraints with the side chain of Asn-170 as well as the main chain nitrogen of Ser-70, a residue contributing to the oxyanion hole. We suggest that hydrophobicity could be the main factor responsible for the kinetic properties of Met69Leu (IRT-5), as no steric effects could be detected by molecular modelling. Hydrophobicity and steric constraints are combined in Met69Ile and Met69Val, IRT-I69 and IRT-6, respectively.
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PMID:Clinical inhibitor-resistant mutants of the beta-lactamase TEM-1 at amino-acid position 69. Kinetic analysis and molecular modelling. 950 60

In order to observe anisotropically grown crystalline materials perpendicular to a certain preferred orientation, a standard cross-sectional TEM preparation method has been modified. The material is embedded in an organic epoxy resin between two Si-wafers. Plates, needles and tubes lay flat inside the resulting sandwich, which is then cut into slices perpendicular to the wafers. The slices are thinned by mechanical abrading and, finally, by ion milling. Crystals located near the central hole are electron-transparent, and their orientation often allows for an observation along the desired direction. The usefulness of this procedure is demonstrated on the examples of high-Tc superconductors and vanadium oxide nanotubes.
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PMID:A simple and fast TEM preparation method utilizing the pre-orientation in plate-like, needle-shaped and tubular materials 1094 25

The new mesoporous transparent conducting oxide based on indium-tin-oxide, meso-ITO, has been synthesized by a modified sol-gel method, using CTAB as the surfactant. Critical was the employment of triethanolamine to control the rate of hydrolysis and inhibit deposition of the bulk oxides. Removal of the surfactant by calcination yielded a relatively well-ordered worm-hole motif arrangement of pores visible in the TEM and stable to 400 degrees C. BET measurements revealed no hysteresis in the absorption-desorption isotherm, consistent with a narrow pore-size distribution (between 20 and 40 A depending on the In:Sn ratio); surface areas ranged between 270 and 310 m2/g. This colorless material is the first mesoporous oxide exhibiting substantial framework conductivity, with a conductivity at 25 degrees C of 1.2 x 10-3 S/cm. This distinguishes it from mesoporous mixed-valence transition-metal oxides that exhibit weak hopping semiconductor behavior and much lower conductivity.
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PMID:Synthesis and characterization of mesoporous indium tin oxide possessing an electronically conductive framework. 1212 Oct 78

The inelastic mean free path of 120 keV electrons in vitrified ice layers has been determined in an energy-filtering TEM. From the ratio of the unfiltered and zero-loss-filtered image intensities recorded with a slow-scan CCD camera, the relative sample thickness t/Lambda can be calculated. For calibration, the geometric ice thickness was measured by imaging a tilted view of a cylindrical hole which had been burnt into the ice layer. The total inelastic mean free path was found to be 161 nm, and the partial inelastic mean free path for an acceptance angle of 4.2 mrad was 232 nm. These results were built into a standard protocol for use in cryo-electron microscopy allowing on-line measurements of local ice-layer thicknesses by zero-loss-filtered/unfiltered imaging.
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PMID:Determination of the inelastic mean free path of electrons in vitrified ice layers for on-line thickness measurements by zero-loss imaging. 1255 83

High-resolution electron energy-loss spectroscopy in a transmission electron microscope is a very powerful method for the study of electronic structure of materials. The fine structure of Ga L(2,3) and N ionization edges in c-GaN and h-GaN was studied using a TEM equipped with a monochromator and high-resolution energy spectrometer. The experimental results were compared with the results of calculation based on the density functional theory using the Wien2k code and show that the best fit is achieved when the core hole effect is taken into account. The effect of the core hole value and the supercell size on the energy-loss near-edge structure have been investigated. A different behaviour was found for c-GaN and h-GaN: better agreement is obtained for a 0.5 core hole for h-GaN and for a full core hole for c-GaN. The anisotropic behaviour of the experimental spectra and calculated spectra for h-GaN have been studied and the "magic" angle was determined.
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PMID:Investigation of hexagonal and cubic GaN by high-resolution electron energy-loss spectroscopy and density functional theory. 1504 5

Titania is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of its excellent UV light absorption properties. Its high photocatalytic activity, however, facilitates the generation of reactive oxygen species, which can oxidize and degrade other ingredients during its formulation, raising safety concerns. Dense coating of titania nanoparticles with a silica layer could help in depression of their photocatalytic activity by disturbing the formation of radicals produced by the reaction of oxygen and/or water with the electron-hole pair. Depression of the high photocatalytic activity of titania necessitates that the silica shell has to be thick, with minimum microporosity. Coating parameters were optimized to attain greater amounts of precipitated silica and thicker shells with lower microporosity, which in turn resulted in great depression of photocatalytic activity. Silica-coated titania nanoparticles were characterized by TEM, XPS, FT-IR, EDX, and microporosity measurements. The photocatalytic activity was evaluated for the coated powder to investigate the efficiency of the silica coating as well.
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PMID:Control of silica shell thickness and microporosity of titania-silica core-shell type nanoparticles to depress the photocatalytic activity of titania. 1669 69


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