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At least 775 records · Page 43Linked to original sources
PubMed1999

Dihydrolipoic acid maintains ubiquinone in the antioxidant active form by two-electron reduction of ubiquinone and one-electron reduction of ubisemiquinone.

Dihydrolipoic acid (DHLA) is a constituent of cellular energy metabolism, where it cycles between the oxidized and reduced form. The two thiol residues of DHLA make this biomolecule susceptible to most radical species and prevent Fenton-type reactions by chelating free iron. In this study we present a novel mode of action by which DHLA exerts antioxidant function in combination with coenzyme Q (ubiquinone). DHLA was found to reduce ubiquinone to ubiquinol by the transfer of a pair of electrons, thereby increasing the antioxidant capacity of coenzyme Q in biomembranes. In addition, ubisemiquinone, which was earlier shown to be an active oxygen radical source when existing in the anionic form, is removed from equilibrium by the addition of a single electron from DHLA. The high reactivity of DHLA with this potentially deleterious ubisemiquinone species not only prevents the formation of prooxidants, it also keeps ubiquinone in its antioxidant active form. Experimental data of this study demonstrate a superadditive effect of ubiquinone in combination with DHLA in preventing peroxidation of biomembranes.

Animals↗
PubMed1997

Correlation of vascular smooth muscle cell morphology observed by scanning electron microscopy with transmission electron microscopy.

Smooth muscle cell (SMC) morphology was studied in rat large mesenteric artery using scanning electron microscopy (SEM), after removal of connective tissue elements with the OsO4/HCl method. Transmission electron microscopy (TEM) was used to correlate the findings of SEM and to assess the effects of digestion on cell ultrastructure. When viewed with SEM, relaxed SMC possessed a smooth, regular surface morphology with longitudinal striations or grooves. TEM examination of cross-sectional profiles of SMC suggested that these striations corresponded to the arrangement of membrane dense bodies within the SMC. The presence of cell contacts among SMC as observed with SEM were confirmed using TEM. Two types of SMC contacts were found: simple appositional contacts and interdigitations. Gap junctions were not observed between SMC in the media. Although structures suggesting nerve networks were observed in the medial-adventitial border with SEM, this could not be confirmed using TEM as a result of alteration in cell ultrastructure with the digestive method. We conclude that the OsO4/HCl method, although useful for SEM, is not suitable for TEM study, because it caused significant alterations of SMC ultrastructure such that organelles and other structures were no longer evident when viewed with TEM.

Animals↗
PubMed1994

Analysis of electron microscope images and electron diffraction patterns of thin crystals of phi 29 connectors in ice.

Images and diffraction patterns of frozen-hydrated thin crystals of phi 29 connectors were recorded using low dose microscopy and diffraction. The resolution obtained in two cases was 7 and 4 A, thus showing the suitability of this specimen for high-resolution studies. Seven of the best images and three of the best electron diffraction patterns were analysed semiquantitatively. The best image showed the presence of two connectors per unit cell (165 A x 165 A), each having an internal 4-fold axis and being related to one-another by 2-fold and 2-fold screw axes in the space group p42(1)2. Internal phase comparison within the best image showed good phase residuals for p42(1)2 and all its sub-groups. The other images were consistent with this interpretation taking into consideration the possible crystal tilt and specimen drift. We conclude that the most likely crystal space group is p42(1)2. Electron diffraction patterns were consistent with this assignment, but none of the patterns showed the precise 422 symmetry expected, almost certainly because the crystals were slightly tilted (2 to 5 degrees).

Bacillus Phages↗
PubMed1990

An electron microscopic and electron probe study of the microcirculation in cold-induced oedema.

An ultrastructural study of adult mongrel dogs and cats was made to evaluate the changes in the microcirculation during cerebral oedema formation. Two to five cold injuries were made in one hemisphere in dogs and one lesion was made in cats. In several dogs arterial hypertension was induced with a balloon in the aorta. Intracranial pressure (ICP) and water content were measured. The specimens from the oedematous region were studied with transmission electron microscopy (TEM) and electron probe x-ray micro-analysis (EPMA). The TEM data showed swelling of the endothelium and astrocytic foot processes, enlarged perivascular spaces and increased number of endothelial vesicles. The EPMA findings indicated increases in Fe and Ca content in the perivascular spaces. In some cases, the amount of chloride in red cells was increased. The altered distributions of these metals suggested tissue injury and impairment of red cell and vessel wall functions.

Animals↗
PubMed1995

Scanning electron microscopy-electron probe microanalysis study of the interface between apatite and wollastonite-containing glass-ceramic and rabbit tibia under load-bearing conditions after long-term implantation.

Glass-ceramic implants containing oxy- and fluoroapatite [Ca10(PO4)6(O, F2)] and beta-wollastonite (CaSiO3) were studied under load-bearing conditions in a segmental replacement model in the tibia of the rabbit. A 16-mm segment of the middle of the tibial shaft was resected at a point distal to the junction of the tibia and the fibula. The defect was replaced by a 15 mm-long hollow, cylindrical implant that was fixed by intramedullary nailing using Kirschner wire. The implants were 9 mm in diameter and 15 mm long bearing a central hole 3.05 mm in dianeter. The rabbits used were killed 6 months, 1 year, 18 months, and 2 years after implantation. The interface between the bone and the glass-ceramic was investigated by scanning electron microscopy-electron-probe microanalysis (SEM-EPMA). None of the glass-ceramic implants broke, and the glass-ceramic had bonded directly to the bone tissue without any intervening soft tissue. A calcium-phosphorus layer (Ca-P layer) was observed at the glass-ceramic/bone interface. This layer was 30-100 microns thick at 6 months after implantation, 60-110 microns thick at 1 year after implantation, 80-200 microns thick at 18 months, and 120-350 microns thick at 2 years. At the lateral surface of the glass-ceramic uncovered by the bone, the calcium-phosphorus layer was 50-80 microns thick at 6 months after implantation, 250-450 microns thick at 1 year, 300 approximately 400 microns thick at 18 months, and 300 microns thick at 2 years. The thickness of the calcium-phosphorus layer increased moderately after long-term implantation. However, it was difficult to estimate the rate of increase in the thickness of calcium-phosphorus layer.

Animals↗
PubMed2001

Ultrastructural study of polyspermy during early embryo development in pigs, observed by scanning electron microscope and transmission electron microscope.

Polyspermy is generally considered a pathological phenomenon in mammals. Incidence of polyspermy in porcine eggs in vivo is extremely high (30-40%) compared with other species, and polyspermy rate in the in vitro fertilized eggs in pigs can reach 65%. It is still unknown whether polyspermy to a certain degree is a physiological condition in pigs, and whether porcine eggs have any capability with which to remove the accessory sperm in the cytoplasm. The objectives in the present study are to observe the ultrastructural changes of accessory sperm during early embryonic development in pigs. A total of 58 normal, early embryos at one-, two, three-, and four-cell and morular stages were collected from gilts and were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface ultrastructure showed that sperm fusion with the zona pellucida was a continuous process during one-, two-, three-, and four-cell and morular stages, as observed by the SEM. Accessory sperm were present in the cytoplasm of cleaved embryos. The sperm heads in the cytoplasm of cleaved embryos did not decondense. TEM revealed the presence of a condensed sperm head within a lysosome (or phagolysosome) in a three-cell embryo. These observations suggest that polyspermy may be a physiological condition in pigs and that early embryos may develop to term if accessory sperm do not interrupt the embryo genome. Furthermore, lysosome activity could be another physiological mechanism for removing accessory sperm in the cytoplasm of fertilized eggs and cleaved embryos after fertilization in pigs.

Animals↗
PubMed1980

Electron spin echo studies on chloroplasts. Spectral characteristics of electron transport components and light-induced transients.

Electron-spin resonance echoes are used to study the complex overlapping ESR spectra of whole chloroplasts. By varying the repetition rate of the microwave pulse sequence, delay time, and pulse width, signals with different longitudinal and transverse relaxation times were extracted. We have identified the echo signals due to plastocyanin and ferredoxins. In addition, we have found a strong signal at g = 4.3, that possibly arises from distorted cytochrome, and weak signals in the region g = 6-9. The strong echo signal at g = 2.0047 (Signal II), is made up of at least three "dark" components that differ in their relaxation times. Upon illumination at 1.2 K several of the echo signals including Signal II show reversible light-induced components. The kinetics of these transients depend on the addition of 3(3,4-dichlorophenyl)-1,1-dimethyl urea. Part of the transients are believed to arise from cyclic electron flow around Photosystem I.

Chloroplasts↗
PubMed1989

Study of the vaginal mucous membrane following tampon utilisation; aspect on colposcopy, scanning electron microscopy and transmission electron microscopy.

The effect of periodic tampons was studied in 17 young women during the menstrual and inter-menstrual cycle. Biopsies (n = 19) were analysed on scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of medium absorbant tampons was compared with that of super-absorbant tampons. On colposcopy, dryness was noted in 89% cases, peeling in 47% cases. Microulcerations were observed only once (5%). Dryness and peeling was most often encountered with the super-absorbant tampons and during the inter-menstrual phase. TEM revealed cellular destruction affecting all layers of the epithelium: lysis of superficial and intermediate cells, destruction of desmosomes accompanied by the creation of inter-cellular spaces, lipidic vacuoles in the lysed cells. SEM revealed epithelial peeling with cleavage and severe cellular desquamation. Cellular anomalies were common at the level of the cytoplasmic membrane, which presented either defects, a porous aspect, or appeared swollen by air-bubbles.

Adult↗
PubMed1993

Auger electron spectroscopy of dentin: elemental quantification and the effects of electron and ion bombardment.

Auger electron spectroscopy was used in this investigation to quantify the elemental composition of various dentin surfaces. The surfaces included the "smeared layer," produced by abrasion, as well as surfaces prepared by fracturing in vacuum and in air. Quantification was aided by spectra obtained from standard samples of the two main components of dentin, hydroxyapatite, and collagen. Experimental conditions were found whereby the samples could be analyzed without conductive coatings. Ion sputter etch rates were measured for dentin, hydroxyapatite, and collagen. Under the conditions used here, it was observed that collagen etched at a rate approximately five times greater than hydroxyapatite. Auger spectra of the sputtered surfaces indicated significant ion beam-induced sample changes in collagen and dentin; no significant changes were found with hydroxyapatite. The results of this investigation demonstrate that Auger electron spectroscopy can be used to characterize dentinal surfaces and that ion sputtering can cause changes in the surface composition of dentin.

Collagen↗
PubMed1988

Mössbauer spectroscopy, electron microscopy and electron diffraction studies of the iron cores in various human and animal haemosiderins.

Mössbauer spectroscopy has indicated significant differences in the iron-containing cores of various haemosiderins. In the present study, haemosiderin was isolated from a number of animal species including man. In addition, haemosiderin was isolated from patients with primary idiopathic haemochromatosis or with secondary (transfusional) iron-overload. The iron cores of the animal and normal human haemosiderin appear to be very similar by Mössbauer spectroscopy, and the electron diffraction data indicate a ferrihydrite structure similar to that of ferritin cores. The haemosiderin isolated from secondary iron-overload shows anomalous behaviour in its temperature-dependent Mössbauer spectra. This can be understood in terms of the microcrystalline goethite structure of the cores as indicated by electron diffraction. The haemosiderin cores obtained in the case of primary haemochromatosis have an amorphous Fe(III) oxide structure and show Mössbauer spectra characteristic of a magnetically disordered material, which only orders at very low temperatures.

Animals↗
PubMed2005

Study of electron donor-acceptor complexes of tri-n-octyl amine with [60]- and [70]fullerenes and some other electron acceptors by absorption spectrophotometric method.

Electron donor-acceptor (EDA) complexes of tri-n-octylamine (TOA) with [60]- and [70]fullerenes and some other electron acceptors have been studied in chloroform medium by absorption spectrophotometric technique. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potential of TOA was determined utilizing CT transition energy. Oscillator strengths, transition dipole strengths and resonance energies for all the complexes have been calculated. [60]Fullerene/TOA and [70]fullerene/TOA complexes are found to decay slowly with time. Kinetics of these reactions have been studied and activation energies for such processes have been estimated. Ab initio calculations suggest that complexation of [70]fullerene with TOA is enthalpy favoured.

Absorption↗
PubMed2001

Photoreducible high spin iron electron paramagnetic resonance signals in dark-adapted Photosystem II: are they oxidised non-haem iron formed from interaction of oxygen with PSII electron acceptors?

An electron paramagnetic resonance (EPR) signal near g=6 in Photosystem II (PSII) membranes has been assigned to a high spin form of cytochrome (Cyt) b(559) (R. Fiege, U. Schreiber, G. Renger, W. Lubitz, V.A. Shuvalov, FEBS Lett. 377 (1995) 325-329). Here we have further investigated the origin of this signal. A slow formation of the signal during storage in the dark is observed in oxygen-evolving PSII membranes, which correlate with the oxidation of Fe(2+) by plastosemiquinone or oxygen. Removal of oxygen inhibits formation of the high spin iron signal. The g=6 EPR signal is photoreduced at cryogenic temperatures and is restored slowly by subsequent dark storage at 77 K. The amplitude of the photoreduced signal increases as the pH is lowered, which shows that the origin is not the hydroxyl ligated Cyt b(559) species proposed previously. Different cryoprotectants also influence the amplitude and lineshape of the high spin iron signal in a manner suggesting that smaller cryoprotectants can penetrate the iron environment. A correlation between the high spin iron and g=1.6 EPR signal assigned to an interaction involving the semiquinones of Qa and Qb is shown. It is concluded that the appearance of the high spin iron signal in oxygen-evolving PSII membranes involves reduced PSII electron acceptors and oxygen and suggests that the signal is from the non-haem iron of PSII.

Benzoquinones↗
PubMed1998

Electron entry in a CuA mutant of cytochrome c oxidase from Paracoccus denitrificans. Conclusive evidence on the initial electron entry metal center.

A cytochrome c oxidase subunit II C216S mutant from Paracoccus denitrificans in which the CuA site was changed by site-directed mutagenesis to a mononuclear copper site [Zickermann, V., Wittershagen, A., Kolbesen, B.O. and Ludwig, B. Biochemistry 36 (1997) 3232-3236] was investigated by stopped-flow spectroscopy. Contrary to the behavior of the wild type enzyme, in this mutant cytochrome a cannot be reduced by excess cytochrome c in the millisecond time scale in which cytochrome c oxidation is observed. The results conclusively identify and establish CuA as the initial electron entry site in cytochrome c oxidase. Partial rapid reduction (ca. 20%) of the modified CuA site suggests that the mononuclear copper ion has a redox potential ca. 100 mV lower than the wild type, and that internal electron transfer to cytochrome a is > or = 10(3)-fold slower than with the wild type enzyme.

Copper↗
PubMed1998

Assessment of heat and storage conditions on gamma-ray and electron beam irradiated UHMWPE by electron spin resonance.

Electron spin resonance (ESR) spectroscopic study was undertaken to explore the nature of any remaining radicals in ultra-high molecular weight polyethylene (UHMWPE) after irradiation with gamma-rays and electron beams to a dose of 25 KGy in air or N2 environment. The decay of radicals was studied by observing the ESR intensity change as a function of time. The following post-irradiation conditions were employed: (1) storage in air or N2 at 25 degrees C, and (2) heat treatment in air or N2 at 80, 100, and 120 degrees C for time intervals up to 8 h. The study suggests that radicals remaining trapped in the matrix of UHMWPE could be dramatically scavenged by heat treatment, independently of the atmosphere during irradiation and the heating process. The melting temperature and mechanical properties of irradiated UHMWPE under the experimental conditions employed were shown not to alter significantly by heat treatment, except in the presence of air.

Biocompatible Materials↗
PubMed1997

Electron probe analysis and biochemical characterization of electron-dense granules secreted by Entamoeba histolytica.

The interaction of Entamoeba histolytica with collagen induces the intracellular formation and release of electron-dense granules (EDGs) containing collagenase activity which are important in the pathogenicity of this parasite. Purified EDGs contain at least 25 polypeptides with acidic pIs, nine gelatinase activities, small molecules, including inorganic phosphate (Pi), pyrophosphate (PP) and other elements, including Na, Mg, S, Cl, K, Ca and Fe as measured by scanning transmission electron microscopy. Six of these polypeptides with apparent molecular weights of 108, 106, 104, 97, 68 and 59 kDa and two protease activities with apparent molecular weights of 40 and 85 kDa were detected exclusively in the EDGs and were not observed in total trophozoite extracts. Actin was also detected in the EDGs. Therefore, EDGs are a complex of mainly cationic proteins, which contains numerous proteolytic activities, actin and small molecules such as P(i), PP and cations.

Actins↗
PubMed2002

In situ ageing of fine beech roots (Fagus sylvatica) assessed by transmission electron microscopy and electron energy loss spectroscopy: description of microsites and evolution of polyphenolic substances.

Root biomass is quantitatively and qualitatively important in most ecosystems, but its contribution to the pool of organic matter in the soil is not clear. This work was designed to specify root ageing on an ultrastructural scale by transmission electron microscopy combined with microanalysis by electron energy loss spectroscopy. This approach is very suitable for studying the soil/plant interface, and for semi-quantitative analysis of the evolution of polyphenolic substances during root evolution. Three root segments were studied according to a gradient of root senescence: the apical and basal segments of the mycorrhiza and the mycorrhiza-carrier root. Each segment contained a certain proportion of senescent cells, some of which were of fungal origin, and this proportion increased as the root aged. In the three segments, the soil/plant interfaces were differentiated, and the micro-organisms observed in situ were described. Senescent root cells contained many polyphenolic substances and our results showed that these substances were, according to the root segment, differently associated with Ca, N and Si. When all these ultrastructural data are correlated with more global data, they can be usefully applied to root cell physiology, microbiology and pedology. This approach makes it possible to specify the evolution of organic matter in situ in soils whatever its origin.

Cellular Senescence↗
PubMed2000

Bioaccumulation and localization of exogenous cadmium in a teleost by electron microscopy (TEM) and its specific quantitation by electron probe X-ray microanalysis (EPMA).

A cadmium bioconcentration study was carried out in a fresh water teleost, Colisa fasciatus, to study the bioaccumulation kinetics and fate of exogenous cadmium (Cd) in biological tissues. Study shows that on exposure of the fish to a sublethal concentration of cadmium in test water, Cd uptake results in its bioconcentration in gills, liver and muscle tissues. To explore whether the accumulated Cd reaches the membranes or inside the cells, transmission electron microscopy (TEM) of the thin sections of tissues was done after histochemical localization of Cd in cells by modified SST method. TEM studies of sections of gills, liver and muscle tissues showed the deposits of exogenous Cd (visualized as dense clouds) in biological cells. This suggests the presence of free or loosely bound Cd on the membranes and inside the cells, which in the presence of Na2S is converted into insoluble metal sulfides. Electron probe X-ray microanalysis (EPMA) studies confirmed the presence of Cd on the membrane surface as well as inside the cells of bioindicator organs suggesting involvement of membrane transport of exogenous Cd inside the cells and its deposition as loosely bound insoluble metal complexes.

Animals↗
PubMed2000

Photoinduced electron transfer between C70 fullerene and 3,3',5,5'-tetramethylbenzidine studied by electron paramagnetic resonance.

Electron paramagnetic resonance (EPR) in situ spectroscopy was applied in the study of photoinduced electron transfer between 3,3',5,5'-tetramethylbenzidine (TMB) and C70 in different solvent systems. The changes found in UV-vis spectra pointed at ground state charge transfer complex formation [C70-TMB] in benzonitrile. Upon selective excitation of C70 using steady-state monochromatic irradiation with a wavelength of 546 nm, two EPR singlets were observed, which were assigned to C70 mono- and di-anion. In the photochemical and cathodic in situ reductions, identical EPR spectra of anion radicals were obtained. C70 mono-anion was investigated also in frozen 1,2-dichlorobenzene solutions within the temperature range from 110 to 210 K, and at 110 K the anisotropic EPR spectrum of C70 mono-anion was simulated assuming an axially symmetric g-matrix with gparallel - gperpendicular = 0.00165.

Benzidines↗