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PubMed1995

Lipid-protein interactions and assembly of the 16-kDa channel polypeptide from Nephrops norvegicus. Studies with spin-label electron spin resonance spectroscopy and electron microscopy.

The assembly of 16-kDa polypeptide channel units in membranes from the hepatopancreas of Nephrops norvegicus has been studied both by electron microscopy and by the lipid--protein interactions reported with spin-labeled lipids. Membranes prepared by extraction with N-lauroylsarcosine and Triton X-100 have a low lipid/protein ratio (ca. 4-6.5 phospholipids and 1 cholesterol per 16-kDa monomer), and those prepared by alkaline extraction have a higher lipid/protein ratio (ca. 12-16 phospholipids and 3.5-4 cholesterols per 16-kDa monomer). In the membranes extracted with detergents, the protein is assembled in membrane sheets as hexagonally packed hexameric complexes, whereas the alkali-extracted preparations consist of closed vesicles in which the channel complexes are near randomly distributed. The electron spin resonance (ESR) spectra from lipids spin-labeled at the C-14 position of the (sn-2) chain show lower mobility for the membranes extracted with N-lauroylsarcosine than for the alkaline-extracted membranes. At higher temperatures, the ESR spectra reveal a population of lipids whose mobility is restricted by direct interaction with the intramembranous sections of the channel assemblies. The population of protein-associated spin-labeled phosphatidylcholine in the alkali-extracted membranes corresponds to 4-5 phospholipid molecules plus 1 cholesterol molecule per 16-kDa polypeptide monomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Electron nuclear double resonance (ENDOR) of the Qc.- ubisemiquinone radical in the mitochondrial electron transport chain.

We present an electron nuclear double resonance (ENDOR) study of the bound Qc.- ubisemiquinone in the mitochondrial quinol cytochrome c reductase complex. An ENDOR probe specifically modified for insertion into our electron paramagnetic resonance cavity was used for this study. We observed strongly hyperfine-coupled protons whose exchangeable nature indicated they were hydrogen-bonded to the quinone oxygen(s). It is thought that such hydrogen bonds are critical in binding the ubiquinone to protein, in stabilizing its semiquinone form, and in modulating the thermodynamic properties of the bound ubiquinone in the mitochondrial quinol cytochrome c reductase complex. Additional ENDOR features were assigned to protons of the quinone ring itself and to weakly coupled protons that may be associated with nearby amino acids. From very weakly hyperfine-coupled, distant, exchangeable protons there was also ENDOR evidence to suggest proximity and accessibility of the ubiquinone site to the solvent.

Animals↗
PubMed1998

Electron transfer in photosystem I reaction centers follows a linear pathway in which iron-sulfur cluster FB is the immediate electron donor to soluble ferredoxin.

Reaction centers of photosystem I contain three different [4Fe-4S] clusters named FX, FA, and FB. The terminal photosystem I acceptors (FA, FB) are distributed asymmetrically along the membrane normal, with one of them (FA or FB) being reduced from FX and the other one (FB or FA) reducing soluble ferredoxin. In the present work, kinetics of electron transfer has been measured in PSI from the cyanobacterium Synechocystis sp. PCC 6803 after inactivation of FB by treatment with HgCl2. Photovoltage measurements indicate that, in the absence of FB, reduction of FA by FX is still faster than the rate of FX reduction [(210 ns)-1]. Flash-absorption measurements show that the affinity of ferredoxin for HgCl2-treated PSI is only decreased by a factor of 3-4 compared to untreated photosystem I. The first-order rate of ferredoxin reduction by FA-, within the photosystem I/ferredoxin complex, has been calculated from measurements of P700+ decay. Compared to control PSI, this rate is several orders of magnitude smaller (6 s-1 versus 10(4)-10(6) s-1). Moreover, it is smaller than the rate of recombination from FA-, resulting in inefficient ferredoxin reduction (yield of 25%). After reconstitution of FB, about half of the reconstituted photosystem I reaction centers recover fast reduction of ferredoxin with kinetics similar to that of untreated photosystem I. These results support FB as the direct partner of ferredoxin and as the more distal cluster of photosystem I with respect to the thylakoid membrane, in accordance with a linear electron-transfer pathway FX-->FA-->FB-->ferredoxin.

Cyanobacteria↗
PubMed2006

Complexation of copper(II)-Chelidamate: A multifrequency-pulsed electron paramagnetic resonance and electron nuclear double resonance analysis.

Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) techniques were used to obtain structural information about the copper(II)-chelidamate complex. Well-resolved nitrogen ENDOR spectra could be recorded from solid solution samples by using selective excitation of spin packets. Evaluation of nuclear quadrupole and dipolar hyperfine interaction of the directly ligated nitrogen allowed for an identification of the bond direction to the copper ion within the eigen frame of the copper g-matrix. Invoking two-dimensional EPR techniques, additional hyperfine interaction with a "distant" nitrogen spin, identified as resulting from the solvent dimethylformamide (DMF), was observed. The experimental data are only consistent with formation of a stable pseudoplanar copper complex with single solvent ligation via its oxygen atom.

Biophysics↗
PubMed1983

Evidence on intramolecular electron transfer in the MoFe protein of nitrogenase from Klebsiella pneumoniae from rapid-freeze electron-paramagnetic-resonance studies of its oxidation by ferricyanide.

A transient e.p.r. signal with g-values of 2.05, 1.95 and 1.81 was observed in rapid-freezing experiments when Kpl, the MoFe protein of nitrogenase from Klebsiella pneumoniae, was oxidized by ferricyanide or by some dyes. This e.p.r. signal was assigned to the 'P'-centres and, since such signals are characteristics of [4Fe-4S]1+ clusters, provides further evidence for the 'P'-centres being in the [4Fe-4S]0 oxidation level in the dithionite-reduced protein. When 4-10-fold excesses of ferricyanide were used as oxidants, the rate of disappearance of the transient e.p.r. signal was independent of the concentrations of ferricyanide, Kpl or ferrocyanide, i.e. its disappearance was by an intramolecular process. Under some circumstances the g = 3.7 e.p.r. signal from the FeMo-cofactors disappeared at a similar rate. It was concluded that, in these circumstances, the g = 3.7 e.p.r. signal disappears, owing to intramolecular electron transfer to the 'P'-centres in the [4Fe-4S]2+ (P2+) oxidation level, whereas the gav. = 1.933 transient e.p.r. signal from the P1+ centres disappears, owing to a change in its spin state from S = 1/2 to S = 5/2 the rate of this process being maximal when there are two P1+ centres in the half-molecule. The rate of the intramolecular decay of the e.p.r. signals, 4.1 +/- 0.8 s-1, is the same as the rate of enzyme turnover. It is suggested that both processes may be linked to the same conformational change, which triggers, or is triggered by, intramolecular electron transfer.

Electron Spin Resonance Spectroscopy↗
PubMed1988

Cross-linking of the electron-transfer flavoprotein to electron-transfer flavoprotein-ubiquinone oxidoreductase with heterobifunctional reagents.

The mitochondrial electron-transfer flavoprotein (ETF) is a heterodimer containing only one FAD. In previous work on the structure-function relationships of ETF, its interaction with the general acyl-CoA dehydrogenase (GAD) was studied by chemical cross-linking with heterobifunctional reagents [D. J. Steenkamp (1987) Biochem. J. 243, 519-524]. GAD whose lysine residues were substituted with 3-(2-pyridyldithio)propionyl groups was preferentially cross-linked to the small subunit of ETF, the lysine residues of which had been substituted with 4-mercaptobutyramidine (MBA) groups. This work was extended to the interaction of ETF with ETF-ubiquinone oxidoreductase (ETF-Q ox). ETF-Q ox was partially inactivated by modification with N-succinimidyl 3-(2-pyridyldithio)propionate to introduce pyridyl disulphide structures. A similar modification of ETF caused a large increase in the apparent Michaelis constant of ETF-Q ox for modified ETF owing to the loss of positive charge on some critical lysines of ETF. When ETF-Q ox was modified with 2-iminothiolane to introduce 4-mercaptobutyramidine groups, only a minor effect on the activity of the enzyme was observed. To retain the positive charges on the lysine residues of ETF, pyridyl disulphide structures were introduced by treating ETF with 2-iminothiolane in the presence of 2,2'-dithiodipyridyl. The electron-transfer activity of the resultant ETF preparation containing 4-(2-pyridyldithio)butyramidine (PDBA) groups was only slightly affected. When ETF-Q ox substituted with MBA groups was mixed with ETF bearing PDBA groups, at least 70% of the cross-links formed between the two proteins were between the small subunit of ETF and ETF-Q ox. ETF-Q ox, therefore, interacts predominantly with the same subunit of ETF as GAD. Variables which affect the selectivity of ETF-Q ox cross-linking to the subunits of ETF are considered.

Acyl-CoA Dehydrogenases↗
PubMed1998

31P-NMR spectroscopy of human and Paracoccus denitrificans electron transfer flavoproteins, and 13C- and 15N-NMR spectroscopy of human electron transfer flavoprotein in the oxidised and reduced states.

Human and Paracoccus denitrificans wild-type electron transfer flavoproteins have been investigated by 31P-NMR in the oxidised and reduced states. The 31P chemical shifts of the diphosphate moiety of the protein-bound FAD were similar in the proteins and were independent of the redox state. The chemical shifts were remarkably similar to those of ferredoxin-NADP+ reductase and, to a lesser degree, with those of NADPH-cytochrome P-450 reductase. The wild-type human electron transfer apoprotein was reconstituted with [2,4a-13C2]FAD, [4,10a-13C2]FAD, or [U-15N4]FAD. The reconstituted proteins were studied by 13C- and 15N-NMR techniques in the oxidised and reduced states. The chemical shifts were compared with those of free flavin in aqueous solution or in chloroform, and those of flavoproteins published in the literature. In the oxidised state, strong hydrogen bonds exist between residues of the apoprotein and C(2)O and N(5) of FAD. The N(1) atom is also hydrogen bonded and, as shown by X-ray data, involves the C'(4)-OH group of FAD. The sp2 hybridisation of N(10) is small compared to other flavoproteins. In the reduced state, there are strong hydrogen bonds involving C(2)O and N(5) of FAD. The N(1) atom is ionised as observed also in other flavoproteins when investigated by NMR. The intramolecular hydrogen bond between the C'(4)-OH group and the N(1) atom of FAD is maintained in the reduced state, suggesting an involvement in the stabilisation of a certain configuration of the diphosphate group of protein-bound FAD in both redox states. The N(10) atom in the reduced protein is highly sp3 hybridised in comparison to those of other flavoproteins.

Apoproteins↗
PubMed1995

Intranuclear sites of Np 237 in mammalian cells: a study using electron microscopy and electron probe microanalysis.

Two methods, electron microscopy and wavelength dispersive electron probe microanalysis, were used to determine the intracellular sites and chemical form of concentrations of neptunium nitrate 237 after chronic intoxication by the intraperitoneal route in two organs in the rat known to concentrate this element (kidney, liver). Abnormal intranuclear formations in the form of clusters of dense granules containing neptunium, phosphorus, sulphur, and calcium were found in the nuclei of kidney proximal tubule cells and hepatocytes. These formations had a maximum diameter of the order of 2 microns and were located in the central part of the nucleus, away from the nucleolus and peripheral chromatin. Serious nuclear and cytoplasmic ultrastructural lesions are often associated in cells containing neptunium inclusions. The absorbed doses in the kidney and the liver were very low. A relationship between these abnormal intranuclear structures and the carcinogenic effect of neptunium remains to be clarified. This effect is related more probably to the chemical toxicity of Np 237.

Animals↗
PubMed1975

A comparative study in the transmission electron microscope and scanning electron microscope of intracellular structures in sheep heart muscle cells.

The internal cellular structures of the sheep ventricular myocardium have been comparatively studied in the transmission electron microscope (TEM) and in the scanning electron microscope (SEM). For TEM studies the tissue was prepared according to standard methods. Thick sections (10 mum) of paraffin embedded material were, after they had been deparaffinized in toluene, critical point dried, coated with gold and examined in the SEM. The comparative TEM and SEM investigations revealed very good correspondence, and it is evident that the described preparation procedure for SEM has preserved the fine structures of myofibrils, mitochondria, T-Tubules and sarcoplasmic reticulum in an excellent life-like pattern. Of special interest was the three-dimensional demonstration of triads and circumferentially arranged T-tubules.

Animals↗
PubMed1997

An ultracentrifugal approach to quantitative characterization of the molecular assembly of a physiological electron-transfer complex: the interaction of electron-transferring flavoprotein with trimethylamine dehydrogenase.

The interaction between two physiological redox partners, trimethylamine dehydrogenase and electron-transferring flavoprotein, has been characterized quantitatively by analytical ultracentrifugation at 4 degrees C. Analysis of sedimentation-equilibrium distributions obtained at 15 000 rpm for mixtures in 10 mM potassium phosphate, pH 7.5, by means of the psi function [Wills, P. R., Jacobsen, M. P. & Winzor, D. J. (1996) Biopolymers 38, 119-130] has yielded an intrinsic dissociation constant of 3-7 microM for the interaction of electron-transferring flavoprotein with two equivalent and independent sites on the homodimeric enzyme. This investigation indicates the potential of sedimentation equilibrium for the quantitative characterization of interactions between dissimilar macromolecules.

Bacteria↗
PubMed1978

Morphological differentiation of the fossil dinosaur bone cells. Light, transmission electron-, and scanning electron-microscopic studies.

The investigation was carried out on the fossil dinosaur bone from before 80 million years. Samples for examination were prepared with specially elaborated methods. Thus the isolated osteocytes of the dinosaur bone, which had previously undergone natural fossilizing processes, were obtained. This permitted their morphological assessment. On the basis of the images obtained in the light, transmission electron, and scanning electron microscopes, two types of osteocytes were distinguished. Type I was characterized by an elongated shape, its length exceeding the width several times; the mean dimensions of this osteocyte amounted to 28.8/7.03 micron. Type II was shorter, its mean dimensions being equal to 20.28/6.88 micron. Moreover, two types of osteocytes processes were differentiated: the first was represented by thick processes, so-called 'axial processes', whose diameter ranged from 0.5 to 1.5 micron, and which, as a rule, departed from the pole of the cell. They ran farther from the mother cell body to more distant osteocytes. The other type consisted of thin processes departing from various points of the cell body in no particular arrangement but always extrapolarly. They branched off in a close vicinity of the mother osteocyte. Their diameter ranged between 0.076 and 0.35 micron.

Animals↗
PubMedDate not supplied

Studies on intranuclear inclusions and nuclear grooves in papillary thyroid cancer by light, scanning electron and transmission electron microscopy.

OBJECTIVE: To successively examine intranuclear inclusions and nuclear grooves in the same papillary thyroid cancer specimens using a light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM). STUDY DESIGN: We stained cells by the Papanicolaou method after fixation in 1.25% glutaraldehyde for LM and then attempted to observe them successively by SEM-TEM after fixation in 2% paraformaldehyde and 2% osmium tetroxide. RESULTS: On SEM, intranuclear inclusions were observed as elevated parts, like hills, and nuclear grooves were observed as deep fissures or shallow cracks, sometimes with a few in one cell. On TEM, both intranuclear inclusions and nuclear grooves seemed formed by the nuclear membranes. Intranuclear inclusions also possessed cytoplasm and/or cytoplasmic organelles within some expanded areas in the nuclear grooves. CONCLUSION: It was evident from our three-step technique that intranuclear inclusions and nuclear grooves were essentially the same structures.

Biopsy, Needle↗
PubMed1990

Optimizing parameters for correlative immunogold localization by video-enhanced light microscopy, high-voltage transmission electron microscopy, and field emission scanning electron microscopy.

Correlative video-enhanced light microscopy, high-voltage transmission electron microscopy, and low-voltage high resolution scanning electron microscopy were used to examine the binding of colloidal gold-labeled fibrinogen to platelet surfaces. Optimal conditions for the detection of large (18 nm) and small (3 nm) gold particles are described.

Blood Platelets↗
PubMed1993

Ultrastructural detection of calcium and magnesium in the chromatoid body of mouse spermatids by electron spectroscopic imaging and electron energy loss spectroscopy.

We studied at the ultrastructural level the presence of calcium and magnesium in the chromatoid body (CB) in mouse spermatids. In addition, the presence of these two cations was also examined in the nucleolus. By electron spectroscopic imaging (ESI) and electron energy loss spectroscopic (EELS) analyses on glutaraldehyde/pyroantimonate-fixed material, we showed the association of pyroantimonate precipitate granules containing calcium and/or magnesium with the CB. The granules in both active (primary spermatocytes) and inactive (spermatids) nucleoli contain mainly calcium. Our results confirm that although the pyroantimonate technique used alone suffers from a lack of specificity, it can be useful for in situ immobilization of different cations that are further resolved with methods of elemental analysis. Without pyroantimonate fixation, only very few spots containing calcium can be localized by ESI and EELS.

Animals↗
PubMedDate not supplied

Correlative light optical, scanning electron, and transmission electron microscopy of skeletal muscle in muscular dystrophy and muscular atrophy: a pilot study.

Biopsies of skeletal muscle from three different cases of muscular dystrophy and one case of spinal muscular atrophy that has been fixed with Karnovsky's fluid were either routinely prepared for scanning electron microscopy (SEM) or were frozen to -20 degrees C and sectioned on a steel knife in a cryostat at 5-10 micrometer. The sections were coverslipped and examined using a light microscope equipped with polarizing optics (Pol). After areas were selected, the sections were prepared for SEM and thereby examined. The tissues on the slides that had been observed with light microscopy (LM) and SEM were prepared further for transmission electron microscopy (TEM) by infiltrating them with Epon and cutting sections at approximately 100 nm on an ultramicrotome. It is shown that the stage of contraction in one pathologic myofiber may vary along its length. The following advantages may be realized by using correlative (Pol leads to SEM leads to TEM) microscopy on skeletal muscle biopsies: 1) lesions can be differentiated from "normal" surrounding tissue; 2) doubtful structures can be reexamined with the SEM and TEM; and 3) the SEM image of different states of muscle contraction can be reinterpreted in the light of the Pol or TEM image.

Adolescent↗
PubMedDate not supplied

Renal hemosiderosis due to thalassemia: a light and electron microscopy study with electron probe X-ray microanalysis.

A kidney biopsy specimen with pronounced hemosiderosis from a patient with beta-thalassemia major was studied by light and electron microscopy, including X-ray microanalysis. Ferritin was absorbed from the glomerular ultrafiltrate through the parietal epithelial cells and the tubular epithelial cells and from the blood through the endothelial cells. It was transported in siderosomes into the surrounding basal lamina, where electron-dense deposits of hemosiderin were found in the outer part of the lamina densa and the reticular lamina. Fibrosis was seen as a reaction to the iron followed by severe atrophy of affected structures.

Adolescent↗
PubMedDate not supplied

Heat-induced damage to HeLa-S3 cells: correlation of viability, permeability, osmosensitivity, phase-contrast light-, scanning electron- and transmission electron-microscopical findings.

The responses of HeLa S-3 to mild hyperthermia for relatively critical times at 43 and 45 degrees C were analysed in detail, including growth and colony-forming ability, permeability, osmotic sensitivity and microscopical appearances. For comparative purposes lower temperatures (e.g. 41 degrees C) and higher temperatures (50 and 55 degrees C) were used in some experiments. The evidence from many different aspects, including scanning and transmission electron microscopy, suggests that critical heat exposures do not per se cause severe membrane damage and loss of cell integrity, but changes quickly become manifest when cells are 'recovered' by returning to 37 degrees C. Attention is drawn to the ability of heat-treated cells to show osmotic-like swelling and restoration towards normal volume in medium of 30 per cent normal strength, which would not be expected on the hypothesis that hyperthermia primarily disrupts membrane structure and functioning. Ultrastructural changes during and after hyperthermia--including nucleolar changes, the appearance of perichromatin granules, the formation of electron-dense cytoplasmic clusters, and the development of intranuclear actin rods--corroborate and extend other findings. However, mitochondrial changes were found to be particularly significant, appearing early and correlating well with the loss of viability and metabolic functioning found after heat treatment. These include the early development of intramitochondrial dense granules, followed by vesicularization of the cristae, swelling of the intracristal spaces, myelin degeneration and the formation of bodies which could otherwise be mistaken for secondary lysosomes. The findings indicate the need for more intensive investigations of mitochondria and mitochondrial functioning in hyperthermia-induced cell damage, and their careful correlation with the 'recovery' of energy-dependent process in cells subsequently returned to 37 degrees C.

Cell Division↗
PubMed1975

Scanning electron, light, and transmission electron microscopy of intestine of gnotobiotic calf.

Adjacent areas of upper, middle, and lower parts of the small intestine and spiral colon from a 48-hour-old gnotobiotic calf were compared by scanning electron microscopy (SEM), light microscopy (LM), and transmission electron microscopy (TEM). As visualized by all 3 methods, small intestinal histologic features, except for apical location of villous epithelial cell nuclei in sections of upper and middle parts of small intestine, were similar to those described for other species. The colonic surface visualized by SEM was composed of flattened ridges separated by furrows into which opened the crypts of Lieberkühn. The epithelial surfaces of the ridges and the furrows had an extensive microvillous covering and scattered goblet cell openings.

Animals↗