Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A preparational method was developed solving the problem of cross-sectional TEM preparation of thin films and layer systems deposited onto water-soluble substrates. The technique is based on the replacement of the sample onto steady substrate, followed by mechanical and ion beam thinning. Cross-sectional TEM micrographs of Ag and Ag/Ag2Se layers are shown presenting the efficiency of this novel technique.
 ...
PMID:A novel method for the cross-sectional TEM preparation of thin films deposited onto water-soluble substrates. 835 85

In higher plants, cell-cell recognition reactions taking place following pollination allow the selective restriction of self-pollination and/or interspecific pollination. Many of these systems function by regulating the process of water transfer from the cells found at the stigmatic surface to the individual pollen grain. Interspecific pollination studies on the cruciferous weed Arabidopsis thaliana revealed only a broad specificity of pollen recognition such that pollen from all tested members of the crucifer family were recognized, whereas pollen from almost all other species failed to hydrate. Genetic analysis of A. thaliana has identified three genes that are essential for this recognition process. Recessive mutations in any of these genes result in male sterility due to the production of pollen grains that fail to hydrate when placed on the stigma, but that are capable of hydrating and growing a pollen tube in vitro. Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen-stigma recognition system. All three mutations described also result in a defect in the wax layer normally found on stems and leaves, similar to previously described eceriferum (cer) mutations. Genetic complementation and mapping experiments demonstrated that the newly identified mutants are allelic to the previously identified genes cer1, cer3 and cer6. TEM analysis of the ultrastructure of the pollen coating revealed that all of the mutant pollen grains bear coatings of normal thickness and that tryphine lipid droplets are missing in cer1-147, are reduced in size in cer6-2654 and appear normal in cer3-2186.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Identification of genes required for pollen-stigma recognition in Arabidopsis thaliana. 852 81

The structure of TEM-1 beta-lactamase complex with the inhibitor BLIP has been determined at 1.7 angstrom resolution. The two tandemly repeated domains of BLIP form a polar, concave surface that docks onto a predominantly polar, convex protrusion on the enzyme. The ability of BLIP to adapt to a variety of class A beta-lactamases is most likely due to an observed flexibility between the two domains of the inhibitor and to an extensive layer of water molecules entrapped between the enzyme and inhibitor. A beta-hairpin loop from domain 1 of BLIP is inserted into the active site of the beta-lactamase. The carboxylate of Asp 49 forms hydrogen bonds to four conserved, catalytic residues in the beta-lactamase, thereby mimicking the position of the penicillin G carboxylate observed in the acyl-enzyme complex of TEM-1 with substrate. This beta-hairpin may serve as a template with which to create a new family of peptide-analogue beta-lactamase inhibitors.
 ...
PMID:A potent new mode of beta-lactamase inhibition revealed by the 1.7 A X-ray crystallographic structure of the TEM-1-BLIP complex. 860 17

Beta-Lactamases are widespread in the bacterial world, where they are responsible for resistance to penicillins, cephalosporins, and related compounds, currently the most widely used antibacterial agents. Detailed structural and mechanistic understanding of these enzymes can be expected to guide the design of new antibacterial compounds resistant to their action. A number of high-resolution structures are available for class A beta-lactamases, whose catalytic mechanism involves the acylation of a serine residue at the active site. The identity of the general base which participates in the activation of this serine residue during catalysis has been the subject of controversy, both a lysine residue and a glutamic acid residue having been proposed as candidates for this role. We have used the pH dependence of chemical modification of epsilon-amino groups by 2,4,6,-trinitrobenzenesulfonate and the pH dependence of the epsilon-methylene 1H and 13C chemical shifts (in enzyme selectively labeled with [epsilon-13C]lysine) to estimate the pKa of the relevant lysine residue, lysine-73, of TEM-1 beta-lactamase. Both methods show that the pKa of this residue is > 10, making it very unlikely that this residue could act as a proton acceptor in catalysis. An alternative mechanism in which this role is performed by glutamate-166 through an intervening water molecule is described.
 ...
PMID:The catalytic mechanism of beta-lactamases: NMR titration of an active-site lysine residue of the TEM-1 enzyme. 870 Aug 29

The substitution of a methionine for an isoleucine at position 69 (Met69Ile), which causes inhibitor resistance to TEM-type beta-lactamases (IRT-3 and IRT-I69), altered the positions of the Asn-170 and Glu-166 side chains as well as the position of the catalytic water molecule. A novel hydrogen bond between the hydroxyl of Thr-182 and the carbonyl of Glu-64 was expected to be responsible for the increase in the catalytic activity of the IST-T182 and IRT-3 enzymes compared with those of TEM-1 and IRT-169, respectively.
 ...
PMID:Implication of Ile-69 and Thr-182 residues in kinetic characteristics of IRT-3 (TEM-32) beta-lactamase. 889 Nov 61

Suspensions of coated superparamagnetic particles (magnetic fluids, MF) in AC magnetic fields have a pronounced specific absorption rate (SAR) per mass compared to multidomain particles. The aim of the present study was to investigate cellular uptake and the biological effects of AC magnetic field excited bio-compatible magnetic fluids on human carcinoma cells in vitro. One of the fluids tested was a dextran magnetite, which has a very low cyto-toxicity with survival fractions (SF) between 0.8 and 0.9 at concentrations of up to 5 mg ferrite per ml. Human carcinoma cells intracellularly accumulate up to 1 pg ferrite/cell which has been demonstrated by electron microscopy (TEM), X-ray spectroscopy and measurements of intracellular iron. It has been shown that the ferrite core is not altered intracellularly, but many of the dextran shells are degraded which yields particle chains and other aggregates observed in TEM. Semi-solid pellets of the tumour cells were treated with AC magnetic fields (520 kHz, 4-12.5 kA/m) or waterbath hyperthermia at 43 and 45 degrees C, in presence of extracellular and/or intracellular magnetic fluid particles. Although MF heating is produced from individual particles, the survival fractions of MF heated and water bath heated cells are equal. In fact, the extracellular MF particle distribution is homogeneous enough to obtain similar inactivation. In contrast to earlier reports intracellular dextran magnetite particles in AC magnetic fields did not induce cell inactivation. Since the amount of intracellular ferrite should be indeed large enough for cell inactivation, the loss of dextran shells is most probably the main cause of limited effectiveness of the intracellular magnetite particles. The present work has demonstrated that: (1) MFH is able to inactivate tumour cells in vitro to at least the same extent as water bath hyperthermia; and (2) that there is a sensitizer effect of ferrofluids at 43 degrees C probably caused by free ferric ions which induce oxidative stress; and (3) that there is no cytotoxic effect of intracellular dextran magnetite particles 30-180 min excited with AC magnetic fields used in this study. For the new method the term 'magnetic fluid hyperthermia (MFH)' is proposed.
 ...
PMID:Cellular uptake of magnetic fluid particles and their effects on human adenocarcinoma cells exposed to AC magnetic fields in vitro. 895 Jan 52

The catalytic pathway of class A beta-lactamases involves an acyl-enzyme intermediate where the substrate is ester-linked to the Ser-70 residue. Glu-166 and Lys-73 have been proposed as candidates for the role of general base in the activation of the serine OH group. The replacement of Glu-166 by an asparagine in the TEM-1 and by a histidine in the Streptomyces albus G beta-lactamases yielded enzymes forming stable acyl-enzymes with beta-lactam antibiotics. Although acylation of the modified proteins by benzylpenicillin remained relatively fast, it was significantly impaired when compared to that observed with the wild-type enzyme. Moreover, the E166N substitution resulted in a spectacular modification of the substrate profile much larger than that described for other mutations of Omega-loop residues. Molecular modeling studies indicate that the displacement of the catalytic water molecule can be related to this observation. These results confirm the crucial roles of Glu-166 and of the "catalytic" water molecule in both the acylation and the deacylation processes.
 ...
PMID:Site-directed mutagenesis of glutamate 166 in two beta-lactamases. Kinetic and molecular modeling studies. 903 44

Mixtures of water and of the nonionic surfactant C12E8 (octaoxyethyleneglycol monododecylether) have been investigated by time-resolved fluorescence quenching (TRFQ) and transmission electron microscopy at cryogenic temperature (cryo-TEM) to obtain information on the size and shape of the surfactant aggregates and on the microstructure of the mixtures. The studies were performed at surfactant contents and temperatures where the micelles grew significantly and also where the systems undergo phase transitions from micellar-to-cubic upon increasing surfactant content or decreasing temperature and from cubic-to-hexagonal-to-micellar upon increasing temperature. No rapid change or discontinuity was observed in the variation of the aggregation number with the surfactant content or temperature upon crossing the micellar-to-cubic phase boundary nor at the approach of the hexagonal phase from the cubic phase. The results confirmed that the cubic phase consists of spheroidal micelles forming a three-dimensional array. The aggregation numbers at high surfactant content or temperature can be much larger than that of the minimum spherical micelle for a surfactant with a dodecyl chain, suggesting that the micelles should be anisotropic. However, cryo-TEM showed that in the micellar phase the micelles are always spheroidal. These apparently inconsistent results are explained in terms of a partial mixing of the surfactant dodecyl chains and octaoxyethylene head groups which allows for spheroidal micelles of aggregation number much larger than for a surfactant with a dodecyl chain. The results show extensive exchange of material at 40°C, taking place most likely via temporary merging of micelles in micelle clusters then present in the system.
 ...
PMID:Aggregation and Microstructure in Aqueous Solutions of the Nonionic Surfactant C12E8 905 24

Rats poisoned with cadmium acetate during 12 weeks, at a dose of 50 mg/dm3 given in drinking water, were treated with oxygen-ozone mixture as intraperitoneal injection during the last 10 days of the experiment, at a daily dose of 1 cm3 and ozone concentration 40 micrograms/cm3. The mixture was made of medical oxygen with a Bioozon U type apparatus produced by B. Prochazka GmbH, Germany, Reutlingen. Control groups included animals treated with the above mixture with no cadmium, and rats poisoned with cadmium, with no oxygen-ozone treatment. Liver and cardiac muscle were examined in TEM Philips EM 301. Morphological traits of a protective of the mixture against cadmium-poisoning were observed in both those organs. This was expressed as weaker destructive changes within the endoplasmic reticulum, basal cytoplasm and lysosome of the hepatocytes, and additionally as a stabilization of contractile apparatus fibres in the heart myocytes.
 ...
PMID:Ultrastructural studies on organs of cadmium-poisoned rats treated with oxygen-ozone mixture. 907 58

The morphology of the valva portalis renalis of the duck was investigated, using histological, SEM and TEM techniques. The wall thickness of the vena iliaca externa, the vena portalis renalis caudalis, the vena iliaca communis and the vena renalis caudalis was morphometrically evaluated. The blood pressure in these veins was measured using a three-way H2O manometer. The valva portalis renalis was composed primarily of epithelioid cells and lined with endothelium. Throughout the entire valva there was a dense complex of nerve structures made up of fibers and fiber bundles which also extended beneath the endothelium of the valva and around the subendothelial epithelioid cells. The wall thicknesses of the veins supplying the renal portal system (vena iliaca externa and vena portalis renalis caudalis) were greater than those of the vessels collecting the renal refluent venous blood (vena iliaca communis and vena renalis caudalis). In addition, the blood pressure values taken in the vena iliaca externa and the vena portalis renalis caudalis were much higher than those in the vena iliaca communis and the vena renalis caudalis. The above observations suggest that the renal portal system works at higher blood pressure levels than the general venous system and that the valva portalis renalis regulates its aperture in order to maintain a constant blood pressure and a continuous blood flow in the renal portal system vessels, hence avoiding damage to the renal parenchyma caused by pressure overloads.
 ...
PMID:The valva portalis renalis in the duck (Anas platyrhynchos). 914 38


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>