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PubMed1975

Scanning electron microscopy of the wall of the third ventricle of the brain of Rana temporia. II. Electron microscopy of the ventricular surface of the pars ventralis of the tuber cinereum.

Scanning electrom microscopy of the ventricular surface of the pars ventralis of the tuber cinereum of the frog Rana temporaria shows that it can be divided in (1) a dorsolateral area, characterized by the presence of very numerous large, solid, bulbous protrusions (2) a medial area, where the large bulbous structures are completely absent and which is diffusely covered with very numerous cilia, (3) a transiotional area located between the two other regions. The large bulbs, shown by scanning electron microscopy, correspond with the end-bulbs of thick ventricular dendrites of nerve cells revealed by transmission electron microscopy. At least many of these intra-ventricular bulbs are dendritic endings of peptidergic neurosecretory neurons, which have been tentatively identified as adenohypophysiotropic neuro-hormone producing neurons (Derickx et al., 1972, 1973a, 1973b). The structural features of the dendritic endings plead in favour of a possible receptive role.

Animals↗
PubMed1994

Morphological and structural studies of early mineral formation in enamel of rat incisors by electron spectroscopic imaging (ESI) and electron spectroscopic diffraction (ESD).

Morphological and structural analysis of the earliest stage of crystal formation in enamel of rat incisors, by use of energy filtering transmission electron microscopy (EFTEM), has shown needlelike crystallites with a dotlike substructure. We conclude that these dots (nanometer-sized particles) have developed at nucleating, active sites along the non-collagenous matrix proteins in enamel. Calcium and phosphate groups are bound at such "active sites" and develop to nuclei, which grow to these stable dots (nanometer-sized particles). The dots coalesce rapidly in longitudinal direction, along the matrix proteins, with neighbouring dots to form parallel arranged "needlelike" crystallites. These needles grow and coalesce in lateral directions to ribbon-platelike crystallites. In enamel most of the organic substance becomes decomposed and transported to the ameloblasts. Consequently, the ribbon-platelike crystallites can coalesce to form much thicker (hydroxy)-apatite crystals than in dentine. Already in the earliest stage of crystal formation the mineral chains of dots (nanometer-sized particles) and the needlelike crystallites show a parallel orientation in the direction of the c-axis of hydroxyapatite. This is supported by the texture of the 002 reflections in the corresponding electron spectroscopic diffraction patterns (ESD), which appear as the first Bragg reflections.

Animals↗
PubMed1981

Photoreceptor outer segment and retinal pigment epithelium in vitamin E deficient rats. An electron microscopic and electron histochemical study.

The photoreceptor outer segments and retinal pigment epithelium of vitamin E deficient rats were examined by electron microscope using electron histochemical techniques. In rats fed a vitamin E deficient diet for more than 6 months starting 20 days after birth, the photoreceptor outer segment showed vesiculation of the discs near the apical portion of the retinal pigment epithelium. In the retinal pigment epithelium, secondary lysosomes were increased in number. Reaction products of acid phosphatase activity were located in secondary lysosomes in the retinal pigment epithelium and on the disc membranes of the photoreceptor outer segment. These alterations became more prominent with the duration of vitamin E deficiency. It was assumed that the disc degeneration of the photoreceptor outer segment might be due to enhanced activity of lysosomal enzymes in the retinal pigment epithelium and the effect of released lysomal enzymes on the photoreceptor outer segment.

Animals↗
PubMed1983

Co-ordinated electron microscopy and X-ray studies of glycerinated insect flight muscle. I. X-ray diffraction monitoring during preparation for electron microscopy of muscle fibres fixed in rigor, in ATP and in AMPPNP.

Synchrotron radiation was used for low-angle X-ray diffraction to monitor structural changes produced in insect flight muscle during fixation, dehydration and embedding for electron microscopy of thin sections. Fibre bundles were fixed by cold glutaraldehyde in one of three states, namely rigor, ATP or AMPPNP, followed by additional cross-linking treatment. No heavy metals were used before embedding. During fixation-embedding, all specimens lost the continuous actin layer lines of spacing 11-5 nm, shrank 18-21% in lattice spacing, shrank 0.5-2.5% in axial spacings and showed equatorial intensity changes which were similar for all three states, while the well-sampled inner layer lines (39-13 nm) were preserved with different fidelity in each state, highest for rigor and lowest for ATP. In different AMPPNP bundles, these layer lines indicated different degrees of unexplained shift (from slight to total) towards the structure of muscle fixed in ATP. Fixation in ATP caused obvious gain of intensity on 39, 19 and 13 nm layer lines, which can be interpreted as trapping of myosin crossbridge attachments to actin; this artifact was unchanged by seven variations in fixation conditions. Fixation in rigor gave no indication of crossbridge detachment nor of the presence or alteration of any significant population of non-bridging myosin heads. X-ray monitoring allowed selection of best-preserved samples for subsequent electron microscopy. The rapid pattern-recording possible with synchrotron X-ray intensity allowed us to complete and compare experiments with many fibre bundles from a single glycerinated Lethocerus muscle.

Adenosine Triphosphate↗
PubMedDate not supplied

Young Investigator Award presentation at the 13th Annual Meeting of the ESMRMB, September 1996, Prague. A proton-electron double-resonance imaging apparatus with simultaneous multiple electron paramagnetic resonance irradiation at 10 mT.

The detection of free radicals in vivo is very important for the study of many physiologic and pathologic conditions. Free radicals have been implicated in a number of diseases such as ischemia, inflammation, kidney damage, and cancer. Proton-electron double-resonance imaging (PEDRI) allows the indirect detection of free radicals via the Overhauser effect. Nitroxide free radicals used for in vivo PEDRI studies present spectra with two or three lines, but most PEDRI experiments performed to date have used only single-line electron paramagnetic resonance (EPR) irradiation. There is theoretical evidence that simultaneous irradiation of multiple EPR transitions could increase the maximum achievable PEDRI enhancement. From the experimental point of view, this requires the combined use of a suitable multiple-frequency EPR source and a multiple-tuned EPR resonator. A novel radiofrequency (RF) triple-tuned loop-gap resonator for use in PEDRI has recently been developed, and dynamic nuclear polarization (DNP) data were reported. In the present study we describe a new PEDRI apparatus, equipped with a triple-tuned resonator, that is suitable for simultaneous double- or triple-EPR irradiation of nitroxide free radicals. In particular, the details of the EPR hardware used to generate the two or three EPR frequencies are given, and PEDRI images obtained with simultaneous multiple EPR irradiation are shown. Moreover, DNP experimental results showing the increase of the enhancement as a function of the EPR power for single and simultaneous double EPR irradiation are presented. The main goal of this apparatus is to improve the sensitivity and/or to reduce EPR irradiation power in a PEDRI experiment. This is likely to be particularly important in future biologic applications of PEDRI where the applied power must be optimized to reduce sample heating.

Awards and Prizes↗
PubMed1998

Calcium distribution in high-pressure frozen bone cells by electron energy loss spectroscopy and electron spectroscopic imaging.

Subcellular localization of total calcium requires tissue processing that preserves the chemical composition of the samples and a highly sensitive microanalytical technique. In this study rat fetal bone samples were submitted to high-pressure freezing and freeze substitution. Ultrastructural preservation was good in the superficial sections: osteoblasts near the bone mineral had clearly defined plasma and nuclear membranes, dense mitochondria, and numerous ribosomes. Electron energy loss spectroscopy allowed high-resolution calcium-sensitive images to be obtained using ionization edge loss electrons. In biological samples, the Ca-L2,3 signal is superimposed on the carbon edge and artifacts may result from thickness and scattering effects. Therefore the relative thickness was established for each area analyzed (t/lambda <0.5). Background was subtracted using the three-images method, allowing high resolution calcium-sensitive images of intramitochondrial granules and of intracellular compartments, and semiquantitative data from the granules to be obtained. Calcium maps were confirmed by spectra collected on defined areas of the images and the shape of the net Ca-L2,3 edges was compared to the characteristic Ca-L2,3 edge of bone crystals. These procedures will provide new information about total calcium localization in bone cells and the possibility of examining the distribution of other elements.

Animals↗
PubMed2000

Probing the electronic structure of transition metal ion centres in proteins by coherent Raman-detected electron paramagnetic resonance spectroscopy.

The simultaneous excitation of a paramagnetic sample with optical (laser) and microwave radiation can cause an amplitude or phase modulation of the transmitted light at the microwave frequency. The detection of this modulation indicates the presence of coupled optical and electron paramagnetic resonance (EPR) transitions in the sample. Here we report the first application of this technique to a biomolecule: the blue copper centre of Pseudomonas aeruginosa azurin. Using optical excitation at 686 nm, in the thiol to copper(II) charge transfer band, we measure a coherent Raman-detected EPR spectrum of a frozen aqueous solution. Its lineshape is characteristic of the magnetic circular dichroism along each principal g-value axis. This information allows electronic and structural models of transition metal ion centres in proteins to be tested.

Electron Spin Resonance Spectroscopy↗
PubMed1983

Characterization of electron transfer from water to plastocyanin catalyzed by resolved electron transfer complexes from chloroplasts.

The photoreduction of soluble plastocyanin in a homologous reconstituted system requires a resolved Photosystem II preparation and the cytochrome b6-f complex from spinach chloroplasts. Oxygen evolution is linked quantitatively to plastocyanin reduction in the reconstituted system, indicating that water is the electron donor for the photoreduction. The photoreduction is sensitive to inhibitors which specifically interact with the Photosystem II preparation [DCMU: 3-(3,4-dichlorophenyl)-1,1-dimethylurea] as well as those which interact with the cytochrome complex (DNP-INT: 2-iodo-6-isopropyl-3-methyl-2',4,4'-trinitrodiphenyl ether; and DBMIB: 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone). The plastocyanin requirement in the reconstituted system indicated a Km of 4.6 microM and a Vmax of 4.2 mumols plastocyanin reduced per nmol cytochrome f per h. Inhibition curves for DNP-INT and DBMIB show that both are effective inhibitors (50% inhibition at a ratio of inhibitor to cytochrome f of 1.0). The rate of reduction of plastocyanin was found to be stimulated by cations. This dependency was localized in the transfer of electrons from the Photosystem II preparation to the cytochrome complex. These results are considered in terms of organizational aspects of integral protein complexes in thylakoid membranes.

Catalysis↗
PubMed1984

Imidazole, imidazolate, and hydroxide complexes of (protoporphyrin IX)iron(III) and its dimethyl ester as model systems for ferric hemoproteins: electron paramagnetic resonance and electronic spectral study.

The EPR and electronic spectral changes upon titration of systems consisting of (protoporphyrin IX)iron(III) chloride (Fe(PPIX)Cl) or its dimethyl ester (Fe-(PPIXDME)Cl) and imidazole derivatives with tetrabutylammonium hydroxide solution have been measured at 77 and 298 degrees K in various solvents. The EPR and electronic spectra of the melt of Fe(PPIXDME)Cl in imidazole derivatives have been also measured. The imidazole derivatives studied here were imidazole and 4-methyl-, 4-phenyl-, 2-methyl-, 2,4-dimethyl-, 1-methyl-, and 1-acetylimidazole. The spectral changes upon addition of hydroxide were markedly different between the systems containing NH imidazoles (BH), with a dissociable proton, and those containing NR imidazoles (BR), without it. In the former systems, five spectral species were successively formed at 77 degrees K and were assigned to following complexes: [Fe(P)(BH)2]+, Fe(P)(BH)(B), [Fe(P)(B)2]-, Fe(P)(BH)(OH), and [Fe(P)(B)(OH)]-, where P is PPIX or PPIXDME. In the latter systems, initial complex, [Fe(P)(BR)2]+, was found to be changed to final complex, Fe(P)(BR)(OH), through an intermediate at 77 degrees K. At 298 degrees K, both systems were found to react with hydroxide to finally form Fe(P)(OH). The crystal field parameters were evaluated using the EPR g values in low-spin complexes studied here and in hemoproteins. The five regions corresponding to five low-spin complexes could be distinguished in crystal field diagrams.

Chemical Phenomena↗
PubMed1988

A change in the heme stereochemistry of cytochrome c upon addition of sodium dodecyl sulfate: electron paramagnetic resonance and electronic absorption spectral study.

Electron paramagnetic resonance and electronic absorption spectral changes upon addition of sodium dodecyl sulfate (SDS) to ferric and ferrous cytochrome c have been measured at 77 degrees K and at room temperature. The spectral changes upon addition of SDS to ferric cytochrome c were performed, in two steps, from native low-spin to another low-spin spectrum and subsequently to high-spin-like spectrum. On the other hand, the spectral changes upon addition of SDS to ferrous cytochrome c proceeded, in one step, from native low-spin to high-spin spectrum. The high-spin-like spectrum of ferric cytochrome c and the high-spin spectrum of ferrous cytochrome c in the presence of high concentrations of SDS are, respectively, apparently similar to those of ferric and ferrous cytochrome c' at physiological pH in spectral features. These spectral similarities suggest the similarities in the heme stereochemistry and the ground state of heme iron. Further, the spectra of cytochrome c in the presence of SDS varied with the change of pH values. The ferric high-spin-like and ferrous high-spin spectra were stable at neutral pH and below it. Conformational changes of cytochrome c upon addition of SDS are also discussed.

Cytochrome c Group↗
PubMed1989

The one-electron oxidation of porphyrins to porphyrin pi-cation radicals by peroxidases: an electron spin resonance investigation.

For the first time, the enzymatic one-electron oxidation of several naturally occurring and synthetic water-soluble porphyrins by peroxidases was investigated by ESR and optical spectroscopy. The ESR spectra of the free radical metabolites of the porphyrins were singlets (g = 2.0024, delta H = 2-3 G), which we assigned to their respective porphyrin pi-cation free radicals. Several porphyrins were investigated and ranked by the intensity of their ESR spectra (coproporphyrin III greater than coproporphyrin I greater than deuteroporphyrin IX greater than mesoporphyrin IX greater than Photofrin II greater than protoporphyrin IX greater than uroporphyrin I greater than uroporphyrin III greater than hematoporphyrin IX). The porphyrins were oxidized by several peroxidases (horseradish peroxidase, lactoperoxidase, and myeloperoxidase), yielding the same type of ESR spectra. From these results, we conclude that porphyrins are substrates for peroxidases. The changes in the visible absorbance spectra of the porphyrins during enzymatic oxidation were monitored. The two-electron oxidation product, which was assigned to the dihydroxyporphyrin, was detected as an intermediate of the oxidation process. The optical spectrum of the porphyrin pi-cation free radical was not detected, probably due to its low steady-state concentration.

Coproporphyrins↗
PubMed1977

Kinetics of electron transfer between the primary and the secondary electron acceptor in reaction centers from Rhodopseudomonas sphaeroides.

Photoreduction of the two ubiquinone molecules, UQ1 and UQ2, bound to purified reaction center from Rhodopseudomonas sphaeroides induces different absorption band shifts of bacteriochlorophyll and bacteriopheophytin molecules depending on which ubiquinone is photoreduced. This allows us to study electron transfer between UQ1 and UQ2 directly by absorption spectrometry. The results support a model in which electrons are transferred one by one from UQ1 to UQ2 with a half-time 200 micro seconds, and two by two from fully reduced UQ2 to the secondary acceptor pool.

Bacteriochlorophylls↗
PubMed1978

Steady-state kinetics of electron transfer through cytochrome chain of uncoupled submitochondrial particles. II. Influence of pH on kinetics of electron transfer.

pH Dependences of steady-state kinetic parameters of cytochrome chains of submitochondrial particles have been studies. It has been shown that the lifetimes of activated states (tau) of the pairs of cytochromes b leads to c1 and a leads to a3 have different pH dependences; those for the c1 leads to c and c leads to a cytochrome pairs being similar. The rate constants for the non-activated state of the respiratory chains decreased for the b leads to c1 pair and increased for the a leads to a3 pair when the pH value was increased. The values of pK calculated from these dependences for the pairs b leads to c1 and a leads to a3 were 7.2 and 8.9, respectively. It has been supposed that the ratio of activated to non-activated electron carriers may be controlled by the local pH value in the mitochondrial membrane, the latter being dependent upon the rate of electron transfer. The kinetic model based on this assumption allows one to explain the experimental dependences on pH of the rate constants for cytochromes b leads to c, and a leads to a3. The values of the diffusion rate constants for H+ and OH- ions in the mitochondrial membrane estimated from these kinetic data obtained in this study were 10(4)--10(5) s-1 and 10(2)--10(3) s-1, respectively.

Cytochrome c Group↗
PubMed1979

Primary and secondary electron donors in photosystem II of chloroplasts. Rates of electron transfer and location in the membrane.

Absorption changes at 820 or 515 nm after a short laser flash were studied comparatively in untreated chloroplasts and in chloroplasts in which oxygen evolution is inhibited. In chloroplasts pre-treated with Tris, the primary donor of Photosystem II (P-680) is oxidized by the flash it is re-reduced in a biphasic manner with half-times of 6 microseconds (major phase) and 22 microseconds. After the second flash, the 6 microseconds phase is nearly absent and P-680+ decays with half-times of 130 microseconds (major phase) and 22 microseconds. Exogenous electron donors (MnCl2 or reduced phenylenediamine) have no direct influence on the kinetics of P-680+. In untreated chloroplasts the 6 and 22 microseconds phases are of very small amplitude, either at the 1st, 2nd or 3rd flash given after dark-adaptation. They are observed, however, after incubation with 10 mM hydroxylamine. These results are interpreted in terms of multiple pathways for the reduction of P-680+: a rapid reduction (less than 1 microseconds) by the physiological donor D1; a slower reduction (6 and 22 microseconds) by donor D'1, operative when O2 evolution is inhibited; a back-reaction (130 microseconds) when D'1 is oxidized by the pre-illumination in inhibited chloroplasts. In Tris-treated chloroplasts the donor system to P-680+ has the capacity to deliver only one electron. The absorption change at 515 nm (electrochromic absorption shift) has been measured in parallel. It is shown that the change linked to Photosystem II activity has nearly the same magnitude in untreated chloroplasts or in chloroplasts treated with hydroxylamine or with Tris (first and subsequent flashes). Thus we conclude that all the donors (P-680, D1, D'1) are located at the internal side of the thylakoid membrane.

Absorption↗
PubMed1995

One-electron reduction of arenediazonium compounds by physiological electron donors generates aryl radicals. An EPR and spin trapping investigation.

Arenediazonium compounds (ArN2+) are strong oxidizing agents, which upon one-electron reduction decompose, releasing aryl radicals (Ar.). The present studies were undertaken to determine whether reductive fragmentation of ArN2+ can be induced by biologically relevant electron donors. We found that 4-X-Ph-N2+ (where X: -NO2, -Br, -Cl, -OMe and -N(Et)2) decomposes to the respective aryl radicals when reduced by ascorbate, NADH, potassium ferrocyanide, catechol or p-hydroquinone in aqueous solutions. Radical identification was based on analysis of the EPR spectra of spin adducts formed by reaction of these radicals with spin traps 2-methyl-2-nitrosopropane (MNP), 3,5-dibromo-4-nitrosobenzene sulphonate (DBNBS) or 5,5-dimethyl-1-pyrroline N-oxide (DMPO). This study shows that reduction of arenediazonium ions can be a convenient method for generating aryl radicals in aqueous solutions. In addition, this investigation confirms that biological reducing agents are capable of inducing fragmentation of ArN2+ into aryl radicals. This reaction may be pertinent to some biological actions of arenediazonium compounds.

Ascorbic Acid↗
PubMed1984

Electron spin resonance and electron nuclear double resonance studies of cation radicals derived from tocopherol model compounds.

Electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) measurements were performed for the cation radicals obtained from the model compounds of alpha-, beta-, gamma- and delta-tocopherol (vitamin E) by oxidizing the tocopherol precursors in an AlCl3-CH2Cl2 solution. The proton hyperfine coupling constants and g-values were precisely determined. The ENDOR spectra of the cation radicals of alpha-, beta-, gamma- and delta-tocopherol models in CH2Cl2 at -100 degrees C clearly show 10, 6, 6 and 12 different proton hyperfine couplings, respectively. By varying the temperature, the ESR spectra of the alpha- and delta-tocopherol model cations exhibit line-width alternation phenomena characteristic of the hindered rotation of the OH group. However, neither the beta- nor the gamma-tocopherol model cation radical ESR spectra show any sign of an alternating line-width effect. These results are interpreted by assuming that the beta- and gamma- tocopherol model cations are stabilized in the trans and cis conformations, respectively. On the other hand, both the alpha- and delta-tocopherol model cations exist as cis and trans isomers.

Chemical Phenomena↗
PubMed1988

Cryo-electron microscopy of insect flight muscle thick filaments. An approach to dynamic electron microscope studies.

Suspensions of isolated insect flight muscle thick filaments were embedded in layers of vitreous ice and visualized in the electron microscope under liquid nitrogen conditions. The unfixed, unstained, unsupported and fully hydrated filaments were observed under various biochemical conditions. We demonstrate here the first successful application of this method to thick filaments, and show that this is a possible approach to following dynamic processes by rapid freezing and electron microscopy.

Animals↗