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At least 631 records · Page 35Linked to original sources
PubMed1993

Osteogenesis at the dental implant interface: high-voltage electron microscopic and conventional transmission electron microscopic observations.

The osteogenesis of mandibular bone to endosteal dental implants was examined using an in vivo dog model. One half of the implants examined were unloaded implants, with the remaining one half prosthodontically loaded for 6 months. Undecalcified mandibular implant samples were examined with both high-voltage electron microscopy (HVEM) stereology and routine transmission electron microscopy. The osseous interface to integrated implants was shown to vary in its morphology. Mineralized bone was observed directly apposing the implant, often separated from the implant by an electron-dense deposit of approximately 50 nm. Within this densely mineralized matrix, osteocytes were routinely observed. Adjacent areas were shown to contain slightly wider zones of either a less dense mineralized matrix or, alternatively, unmineralized tissue. Other zones consisted of wider unmineralized matrices containing collagen fibers and osteoblasts. These latter zones were consistent with the appearance of an appositional type of bone growth. Because bone is a dynamic, actively remodeling tissue, a varied morphology of the support tissues to dental implant is not unexpected. Areas of mature bone interfacing with successfully integrated implants were demonstrated, as well as areas adjacent to the mature bone that were undergoing remodeling or mineralization. This study has also shown that HVEM stereology is a valuable research tool to investigate the oral tissue interface with dental implants.

Aluminum Oxide↗
PubMed1991

Ferredoxin electron transfer site on cytochrome c3. Structural hypothesis of an intramolecular electron transfer pathway within a tetra-heme cytochrome.

To specify electron exchanges involving Desulfovibrio desulfuricans Norway tetra-heme cytochrome c3, the chemical modification of arginine 73 residue, was performed. Biochemical and biophysical studies have shown that the modified cytochrome retains its ability to both interact and act as an electron carrier with its redox partners, ferredoxin and hydrogenase. Moreover, the chemical modification effects on the cytochrome c3 1H NMR spectrum were similar to that induced by the presence of ferredoxin. This suggests that arginine 73 is localized on the cytochrome c3 ferredoxin interacting site. The identification of heme 4, the closest heme to arginine 73, as the ferredoxin interacting heme helps us to hypothesize about the role of the three other hemes in the molecule. A structural hypothesis for an intramolecular electron transfer pathway, involving hemes 4, 3 and 1, is proposed on the basis of the crystal structures of D. vulgaris Miyazaki and D. desulfuricans Norway cytochromes c3. The unique role of some structural features (alpha helix, aromatic residues) intervening between the heme groups, is proposed.

Amino Acid Sequence↗
PubMed2001

Improved low-energy electron injection systems for high rate electron capture dissociation in Fourier transform ion cyclotron resonance mass spectrometry.

New low-energy electron injection systems based on indirectly heated dispenser cathodes facilitate electron capture dissociation (ECD) in Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. In this joint report, details are presented of the design and performance of these systems on two commercial FTICR instruments, 9.4 T Bruker BioAPEX in Uppsala and 4.7 T IonSpec Ultima in Odense. New results include obtaining meaningful one-scan MS/MS data for isolated precursor ions with millisecond irradiation times. The ECD rate improvement is not only due to the larger total electron current, but the larger emitting area as well.

Amino Acid Sequence↗
PubMed1995

Electron transport phosphorylation driven by glyoxylate respiration with hydrogen as electron donor in membrane vesicles of a glyoxylate-fermenting bacterium.

The syntrophically glycolate-fermenting bacterium in the methanogenic binary coculture FlGlyM was isolated in pure culture (strain FlGlyR) with glyoxylate as sole substrate. This strain disproportionated 12 glyoxylate to 7 glycolate, 10 CO2, and 3 hydrogen. Glyoxylate was oxidized via the malyl-CoA pathway. All enzymes of this pathway, i.e. malyl-CoA lyase/malate: CoA ligase, malic enzyme, and pyruvate synthase, were demonstrated in cell-free extracts. Glycolate dehydrogenase, hydrogenase, and ATPase, as well as menaquinones as potential electron carriers, were present in the membranes. Everted membrane vesicles catalyzed hydrogen-dependent glyoxylate reduction to glycolate [86-207 nmol min-1 (mg protein)-1] coupled to ATP synthesis from ADP and Pi [38-82 nmol min-1 (mg protein)-1)]. ATP synthesis was abolished entirely by protonophores or ATPase inhibitors (up to 98 and 94% inhibition, respectively) indicating the involvement of proton-motive force in an electron transport phosphorylation driven by a new glyoxylate respiration with hydrogen as electron donor. Measured reaction rates in vesicle preparations revealed a stoichiometry of ATP formation of 0.2-0.5 ATP per glyoxylate reduced.

Adenosine Triphosphate↗
PubMed1979

Glomerulonephritis induced by high doses of ovalbumin. Studies by electron microscopy, immunofluorescence and immuno-electron microscopy.

Experimental glomerulonephritis was produced in 16 rabbits by intravenous injections of ovalbumin in high doses (0.1 g/day during the first week, 0.2 g x 6/day during the second). The animals were killed on day 14. At that time all animals had 2--4+ proteinuria and a serum C3 level reduced to about 50% of the control level; 11 animals had a significantly raised blood urea level. In all rabbits the antigen had induced severe proliferative glomerulonephritis. Electron microscopy showed that many of the cells accounting for the hypercellularity were monocytes. Surprisingly, electron dense deposits were few and small, mainly on the subendothelial and subepithelial aspects of the glomerular basement membrane. In all the animals ultrastructural immunoperoxidase technique revealed deposits containing ovalbumin, rabbit IgG and C3. With immunofluorescence sparse deposits were occasionally seen. It is concluded that a severe experimental glomerulonephritis can be produced in a state of antigen excess, with the deposition of immune complexes being minimal. Immuno-electron microscopy is essential, however, in detecting even the smallest animals of deposited immune reactants.

Animals↗
PubMed1991

Enzymatic recycling of oxidized ascorbate in pig heart: one-electron vs two-electron pathway.

Enzymatic systems able to reduce either dehydroascorbate or ascorbyl radical back to ascorbate by "recycling" vitamin C may contribute to lowering the nutritional requirement of it and to increase tissue antioxidant capacity. The activities of two enzymatic activities, GSH-dehydroascorbate reductase (two-electron reduction pathway) and NADH-semidehydroascorbate reductase (one-electron reduction pathway) in pig tissues, have been investigated. The activity of glutathione-dependent reduction of dehydroascorbate, although measurable, appeared negligible taking into consideration the low physiological substrate concentration. On the other hand, the one-electron reduction of ascorbyl radical resulted fast enough to slow down the consumption of the antioxidant vitamin.

Animals↗
PubMed1975

Electron-electron double resonance measurements on xanthine oxidase.

Electron-electron double resonance measurements were carried out on milk xanthine oxidase (xanthine:oxygen oxidoreductase EC 1.2.3.2) and the spectra obtained supported a previous model, based on EPR data, proposing a spin-spin interaction between unpaired electrons associated with Fe-S and Mo. The technique demonstrated that the additional apparently isotropic, splitting in the Mo EPR spectra observed at low temperature is produced by a single site giving two spectra interconverting at a rate consistent with the Fe-S spin lattice relaxation time. Other data concerning the model and the relaxation behaviour of the species are discussed.

Animals↗
PubMed1990

One-electron reduction of chloroperoxidase by radiolytically generated electrons.

Upon irradiation of aqueous ethylene glycol/water solutions of native chloroperoxidase (CPO) with 60Co-gamma rays at 77K one observes the one-electron reduction of the enzyme active site by radiolytically generated thermolyzed electrons. In the present study the first absorption spectrum of a low-spin ferrous form of CPO is reported which has peaks at 438, 532 and 563 nm, similar to those observed previously for cytochrome P-450. All previously described ferrous forms of CPO are high spin. In order to observe the final results of the CPO reaction with electrons, the spectral changes of native enzyme after room temperature-gamma-irradiation have also been investigated. Evidence of changes is also presented probably connected with disruption of the tertiary structure of enzyme, correlated with decrease of enzyme activity.

Chloride Peroxidase↗
PubMed1982

Comparison of solid-phase immune electron microscopy, direct electron microscopy and enzyme-linked immunosorbent assay for detection of rotavirus in faecal samples.

One hundred and fifteen faecal samples from children with gastroenteritis have been examined by solid-phase immune electron microscopy (SPIEM), standard direct electron microscopy and enzyme-linked immunosorbent assay (ELISA). Diluted high-titered anti-(human) rotavirus serum, produced in rabbit by immunization with purified pooled rotaviruses from gastroenteritis patients, was used as antiserum in the immunological tests. The presence of rotavirus was demonstrated in 41 (36%) of the 115 samples by both SPIEM and ELISA. No false positive reactions were seen. By direct electron microscopy rotavirus was detected in 35 (30%) of the specimens. In addition, other gastroenteritis viruses like adeno-, astro- and calicivirus were visualized by this non-specific test in eight samples. The applicability of these three methods in routine diagnostic work is discussed.

Antigen-Antibody Reactions↗
PubMed1985

Radical anions from one-electron-reduced adrenochrome. Detection and identification by electron spin resonance spectroscopy.

Free radicals from the one-electron reduction of adrenochrome have been studied in aqueous solutions. These radicals have been detected and identified by electron spin resonance spectroscopy, using spin stabilization methods (complexation with diamagnetic metal ions) to enhance radical concentrations. It is shown that the radicals have a characteristic ESR spectrum enabling their identification in complex systems. The spin density distribution in the radicals has been studied as a function of complexing metal ions and solvent composition. In the presence of oxidants (e.g., oxygen) the spectrum of the radical is replaced by that derived from the one-electron exidation of adrenochrome.

Adrenochrome↗
PubMed1990

Electron field within an electron field treatment of the scalp or other curved surfaces.

The treatment of a curved surface is a challenge for radiation therapy. This patient had previous treatment with electrons to the "skull cap" area for malignant melanoma. The current task was to design a treatment schema to include the rest of the scalp while avoiding the skull cap. Opposing lateral 6-MeV electron fields were used, as well as two anterior 6-MeV electron fields, one field within the other, to produce an acceptable radiation dose to the tumor volume.

Aged↗
PubMed2004

[Electron transfer reactions: from electrons to drugs].

Electron transfer reactions have been at the heart of great advances in organic and inorganic chemistry and biology since the early work in 1954 by H. Taube (Nobel Chemistry Prize in 1983) and R. Marcus (Nobel Chemistry Prize in 1991). In organic chemistry, a new kind of chain substitution reaction with paramagnetic species was defined and identified as S(RN)1 (substitution, radial-nucleophilic, unimolecular). In our laboratory, choosing more or less complex molecules which possess electron-withdrawing groups and correctly disposed alkylation sites has enabled us to extend this concept to the heterocyclic (S(RN)1 HET) and quinonic (S(RN)1 QUI) series. These studies led us to prepare, under mild operating conditions, highly branched molecules hard to obtain via other pathways and which possess high pharmacological activity in various fields. We have discovered new reaction mechanisms such as LD-S(RN)1 (long-distance S(RN)1) E(RC)1 (elimination radical chain, unimolecular), bis-S(RN)1 and poly-S(RN)1. Moreover, we have developed a new technology using microwaves which increases the interest of electron transfer reactions in medicinal chemistry for drugs synthesis.

Alkylation↗
PubMed1978

Electron spin polarization in photosynthesis and the mechanism of electron transfer in photosystem I. Experimental observations.

Transient electron paramagnetic resonance (EPR) methods are used to examine the spin populations of the light-induced radicals produced in spinach chloroplasts, photosystem I particles, and Chlorella pyrenoidosa. We observe both emission and enhanced absorption within the hyperfine structure of the EPR spectrum of P700+, the photooxidized reaction-center chlorophyll radical (Signal I). By using flow gradients or magnetic fields to orient the chloroplasts in the Zeeman field, we are able to influence both the magnitude and sign of the spin polarization. Identification of the polarized radical and P700+ is consistent with the effects of inhibitors, excitation light intensity and wavelength, redox potential, and fractionation of the membranes. The EPR signal of the polarized P700+ radical displays a 30% narrower line width than P700+ after spin relaxation. This suggests a magnetic interaction between P700+ and its reduced (paramagnetic) acceptor, which leads to a collapse of the P700+ hyperfine structure. Narrowing of the spectrum is evident only in the spectrum of polarized P700+, because prompt electron transfer rapidly separates the radical pair. Evidence of cross-relaxation between the adjacent radicals suggests the existence of an exchange interaction. The results indicate that polarization is produced by a radical pair mechanism between P700+ and the reduced primary acceptor of photosystem I. The orientation dependence of the spin polarization of P700+ is due to the g-tensor anisotropy of the acceptor radical to which it is exchange-coupled. The EPR spectrum of P700+ is virtually isotropic once the adjacent acceptor radical has passed the photoionized electron to a later, more remote acceptor molecule. This interpretation implies that the acceptor radical has g-tensor anisotropy significantly greater than the width of the hyperfine field on P700+ and that the acceptor is oriented with its smallest g-tensor axis along the normal to the thylakoid membranes. Both the ferredoxin-like iron-sulfur centers and the X- species observed directly by EPR at low temperatures have g-tensor anisotropy large enough to produce the observed spin polarization; however, studies on oriented chloroplasts show that the bound ferredoxin centers do not have this orientation of their g tensors. In contrast, X- is aligned with its smallest g-tensor axis predominantly normal to the plane of the thylakoid membranes. This is the same orientation predicted for the acceptor radical based on analysis of the spin polarization of P700+, and indicates that the species responsible for the anisotropy of the polarized P700+ spectrum is probably X-. The dark EPR Signal II is shown to possess anisotropic hyperfine structure (and possibly g-tensor anisotropy), which serves as a good indicator of the extent of membrane alignment.

Chlorella↗
PubMed1984

Electron spectroscopic imaging: parallel energy filtering and microanalysis in the fixed-beam electron microscope.

A new imaging modality in electron microscopy uses energy filtration to produce micrographs with elastically scattered electrons or with electrons that have lost a specific, often characteristic amount of energy in interacting with the specimen. No deleterious effects on microscope performance are encountered. Instead, microanalysis of specimens is made possible with a spatial resolution of 3 to 5 A and a sensitivity of detection of 2 X 10(-21) g corresponding to about 50 atoms of phosphorus. Elements detected range from hydrogen (Z = 1) to uranium (Z = 92). Examples of elemental mapping show membrane structure, DNA within nucleosomes, and RNA within ribosomal particles.

Animals↗
PubMed1980

Electron microscopy: a method for the diagnosis of inherited metabolic storage diseases. Electron microscopy in diagnosis.

In the diagnosis of inherited metabolic diseases, electron microscopy has become an important method complementary to clinical, histological and biochemical assays. The characteristic ultrastructure of stored material as well as the site of accumulation in the cell are shown in a number of metabolic disorders. The most prominent advantages of electron microscopical techniques as compared to alternative techniques are discussed. One of the advantages is the fact that ultrastructural investigation requires only tissue samples of very small size, and another that its results may be obtained within two days. Moreover, transmission electron microscopy permits new and promising analytical methods such as quantitative estimation of organellar changes (morphometry) and energy dispersive X-ray elemental analysis (EDX).

Fabry Disease↗
PubMed2002

New applications of electron diffraction in the pharmaceutical industry: polymorph determination by using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques.

Electron diffraction has been recently used in the pharmaceutical industry to study the polymorphism in crystalline drug substances. While conventional X-ray diffraction patterns could not be used to determine the cell parameters of two forms of the microcrystalline GP IIb/IIIa receptor antagonist roxifiban, a combination of electron single-crystal and synchrotron powder diffraction techniques were able to clearly distinguish the two polymorphs. The unit-cell parameters of the two polymorphs were ultimately determined using new software routines designed to take advantage of each technique's unique capabilities. The combined use of transmission electron microscopy (TEM) and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large-unit-cell, micron-sized) polymorphic pharmaceutical compounds.

Amidines↗
PubMed2002

Elemental mapping in natural rubber latex films by electron energy loss spectroscopy associated with transmission electron microscopy.

Element distribution maps from Hevea brasiliensis natural rubber latex thin films were obtained, by electron energy-loss spectroscopic imaging in a low-energy (80 kV) transmission electron microscope. C, N, O, P, Na, Ca, Mg, Al, Si, and S maps are presented for latex fractionated by centrifugation, either followed by dialysis or not. Most elements forming non-carbon compounds are concentrated in small, electron-dense spots surrounded by a carbon-rich matrix of polymer, thus showing that the rubber is filled with small particles compatible with the polyisoprene matrix. Ca distribution is unique, since it closely parallels the C distribution, evidencing an important role for -COO(-)-Ca2+-COO- ionic bridges in the structure of natural rubber.

Dialysis↗