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PubMed2002

Melanin production and use as a soluble electron shuttle for Fe(III) oxide reduction and as a terminal electron acceptor by Shewanella algae BrY.

Dissimilatory metal-reducing bacteria (DMRB) utilize numerous compounds as terminal electron acceptors, including insoluble iron oxides. The mechanism(s) of insoluble-mineral reduction by DMRB is not well understood. Here we report that extracellular melanin is produced by Shewanella algae BrY. The extracted melanin served as the sole terminal electron acceptor. Upon reduction the reduced, soluble melanin reduced insoluble hydrous ferric oxide in the absence of bacteria, thus demonstrating that melanin produced by S. algae BrY is a soluble Fe(III)-reducing compound. In the presence of bacteria, melanin acted as an electron conduit to Fe(III) minerals and increased Fe(III) mineral reduction rates. Growth of S. algae BrY occurred in anaerobic minimal medium supplemented with melanin extracted from previously grown aerobic cultures of S. algae BrY. Melanin produced by S. algae BrY imparts increased versatility to this organism as a soluble Fe(III) reductant, an electron conduit for iron mineral reduction, and a sole terminal electron acceptor that supports growth.

Cytochromes↗
PubMed1990

Ultrastructural distribution of terbium across capillary endothelium: detection by electron spectroscopic imaging and electron energy loss spectroscopy.

We used terbium as an intravital tracer of permeability pathways across the walls of capillaries in the rete mirabile of the eel swimbladder and in frog mesentery. Terbium was detected in unstained ultra-thin sections by electron density using electron spectroscopic imaging (ESI) and by electron energy loss spectroscopy (EELS). Enhancement of intrinsic contrast in zero loss images (elastically scattered electrons) permitted imaging of membrane-bound compartments and terbium within them which might otherwise have been undetected in counterstained sections. Element-selective imaging with EELS indicated that terbium was associated with heavy electron-dense deposits, but the terbium mass:volume of sections in areas of lighter deposition was insufficient to obtain a terbium signal. In the rete capillaries, terbium was deposited on the luminal surface, throughout vesicular profiles, and in the interstitium, but could not be traced through interendothelial junctions. Fine terbium deposits were detectable throughout apparent vesicular connections across the endothelium. In the frog mesentery, terbium penetrated some but not all interendothelial clefts, and was detectable in small quantities within luminal and abluminal vesicular profiles and in the interstitium. The results indicate that in the rete capillaries, terbium permeates the capillary via a transcellular route. This route may be provided by transient fusions of luminal and abluminal vesicular compartments.

Animals↗
PubMed2002

Stability of electron-beam energy monitor for quality assurance of the electron-beam energy from radiotherapy accelerators.

Information on electron energy is important in planning radiation therapy using electrons. The Geske 3405 electron beam energy monitor (Geske monitor, PTW Nuclear Associates, Carle Place, NY, USA) is a device containing nine ionization chambers for checking the energy of the electron beams produced by radiotherapy accelerators. We wondered whether this might increase the likelihood of ionization chamber trouble. In spite of the importance of the stability of such a quality assurance (QA) device, there are no reports on the stability of values measured with a Geske monitor. The purpose of this paper was therefore to describe the stability of a Geske monitor. It was found that the largest coefficient of variation (CV) of the Geske monitor measurements was approximately 0.96% over a 21-week period. In conclusion, the stability of Geske monitor measurements of the energy of electron beams from a linear accelerator was excellent.

Electrons↗
PubMed1999

Electron density imaging of protein films on gold-particle surfaces with transmission electron microscopy.

BACKGROUND: Surface bound proteins on colloid particles are widely used in biotechnological applications such as diagnostics or separation. Analysis of colloid surfaces by imaging methods provides information on the structure of these protein films, and an understanding of the functional relationships of biomolecules immobilised on solid surfaces. METHODS: In order to visualise protein molecules organised in films on surfaces of nano-sized gold-particles, an electron-microscopic approach based on the scattering absorption contrast of the specimen was applied. RESULTS: Analysing protein conjugated gold particles with a transmission electron microscope, protein films on gold particle surfaces cause a significant scattering absorption contrast based on the materials' electron density. Thus, the thickness of such films becomes directly measurable in planar projection and the shape of these films are visualised without negative staining methods. The insertion of Ruthenium-labelled antibodies instead of non-labelled antibodies as a marker with increased electron-density in these films yields a contrast enhancement of the whole film. Additional labelling with anti-Mouse IgG Gold conjugates localises the position of the surface bound antibodies in such protein films. CONCLUSIONS: The power of transmission electron microscopy to resolve protein-films on colloid surfaces without staining or labelling as a sample preparation procedure has been demonstrated. Thus, this direct method provides an analytical tool for studying protein films and their structural features on particle surfaces.

Animals↗
PubMed1987

Morphometrical evaluation of acute leukemic cells by electron microscopy. Discrepancy between morphological characteristics in FAB classification and electron microscopic morphometry.

Leukemic cells from 39 patients with acute leukemia (20 lymphocytic and 19 myelogenous) were examined by transmission electron microscopy and the nucleus and cytoplasm were measured on the micrographs with a computer-controlled image analyzer. The ratios between the areas of the nucleus and whole cell profile (nucleus/cell ratio), heterochromatin and euchromatin, the nucleolus and nucleus, and the degree of irregularity of the nucleus were compared between the two major types of leukemia studied. Acute lymphocytic leukemia (ALL) cells had a relatively larger nucleus and relatively less cytoplasm than acute myelogenous leukemia (AML) cells, and a greater proportion of the area of the nucleus was occupied by heterochromatin in ALL cells than in AML cells. According to the FAB classification, L1 cells are characterized by narrow, and L2 cells by wide cytoplasm based on light microscopic observation of smeared cells, and we confirmed these features by morphometry of May-Giemsa-stained blood smears. However, by electron microscopy there was no difference in the nucleus/cell ratio between L1 and L2 cells, this constituting a discrepancy between the results obtained by electron and light microscopic morphometry. In addition there was no difference in the degree of nuclear irregularity between L1 and L2 cells. Among AML subtypes, significant differences were observed only in the nucleus/cell ratio between M3 and M1, M2 or M4 cells, and in the heterochromatin/euchromatin ratio between M5 and M1, M2 or M3 cells. In conclusion, electron microscopic morphometry revealed marked differences between ALL and AML, but the differences among their subtypes defined by the FAB classification based on nonmorphometric light microscopy were less evident by electron microscopic morphometry.

Cell Nucleus↗
PubMed1985

Mechanism of electron transfer to coordinated dioxygen of oxyhemoglobins to yield peroxide and methemoglobin. Protein control of electron donation by aquopentacyanoferrate(II).

Reactions of human oxyhemoglobin A with iron(II) compounds have been investigated. Human oxyhemoglobin (HbO2) reacts with aquopentacyanoferrate(II), Fe(II)(CN)5H2O3-, to yield hydrogen peroxide, aquomethemoglobin and Fe(III)(CN)5H2O2-. The reaction follows a second order rate law, first order in the pentacyanide and in HbO2. Since reaction rates are lower in the presence of catalase, the H2O2 produced must promote metHb formation in reactions independent of pentacyanide. Changes in concentrations of effectors (e.g. H+, inositol hexaphosphate, Cl-, and Zn2+), alkylation of beta-93 cysteine with N-ethylmaleimide, and substitution at distal histidine (as in Hb Zurich with beta-63 His----Arg) in each case can markedly affect pentacyanide reaction rates demonstrating a fine control of rates by protein structure. Hexacyanoferrate(II) (ferrocyanide) reacts with HbO2 to produce cyano-metHb as well as aquo-metHb but the reaction with the hexacyanide is much slower than with the aquopentacyanide. Iron(II) EDTA converts HbO2 to deoxy-Hb with no evidence for formation of metHb as an intermediate. These findings support a mechanism in which the pentacyanide anion reacts directly with coordinated dioxygen. One-electron transfers to O2 from both pentacyanide iron(II) and heme iron(II) result in the formation of a mu-peroxo intermediate, HbFe(III)-O-O-Fe(III) (CN)5(3-). Hydrolysis of this intermediate yields metHb . H2O, H2O2, and FeIII(CN)5H2O2-. The reaction of HbO2 with Fe(CN)6(4-) must follow an outer sphere electron transfer mechanism. However, the very slow rate that is seen with Fe(CN)6(4-) could arise entirely from the pentacyanide produced from loss of one cyanide ligand from the hexacyanide. Fe(II)EDTA reacts rapidly with free O2 in solution but can not interact directly with the heme-bound O2 of HbAO2. The dynamic character of the O2 binding sites apparently permits access of the Fe2+ of the pentacyanide to coordinated dioxygen but the protein structure is not sufficiently flexible to allow the larger Fe2+EDTA molecule to react with bound O2. It is necessary for maintenance of the oxygen transport function of the red cell for reductants such as the methemoglobin reductase system, glutathione, and ascorbate to be able to reduce metHb to deoxy-Hb. It is also important for these reductants to be unable to donate an electron to HbO2 to yield H2O2 and metHb. Thus, a mechanistic requirement for the delivery of one-electron directly to the dioxygen ligand, if peroxide is to be produced, enables the protein to protect the oxygenated species from those electron donors normally present in the cell by denying these reductants steric access to coordinated O2.(ABSTRACT TRUNCATED AT 400 WORDS)

Alkylation↗
PubMedDate not supplied

[ESR study of electron transport in photosynthetic systems. VII. Effects of temperature on the processes of electron transport between two photosystems and the structural state of the chloroplast membrane].

Redox transients of P700 in bean chloroplasts induced by far-red continuous light and brief flashes (t1/2 = 7 musec) of white light were studied under various temperatures. It has been shown that light-induced electron transport between two photosystems occurs at temperatures from -5 degrees to 45 degrees. At temperature interval 5 divided by 30 degrees photosystem 2 donates electrons to P700+ in response to the flash with the maximum efficiency. The number of electrons donated from photosystem 2 does not depend on the temperature in the range 5 divided by 30 degrees. The rate of electron transport between photosystems increases when the temperature is increased from -5 degrees to 20 degrees and does not depend on the temperature above 20 degrees. Structural states of the lipid region of the thylakoid membrane were studied by the spin label method. It was shown that the flexibility and the rate of molecular motion of different spin-labeled fatty acids were increased after temperature variations from -10 degrees to 50 degrees. A correlation between the structural state of the lipid region of thylakoid membrane and the rate of electron transport was found.

Cell Membrane↗
PubMed1998

Electron paramagnetic resonance and electron nuclear double resonance studies of X-irradiated crystals of cytosine hydrochloride. Part I: free radical formation at 10 K after high radiation doses.

Anhydrous single crystals of cytosine hydrochloride (protonated at N3) have been X-irradiated at 10 K and studied using K-band EPR, ENDOR and FSE spectroscopy. At least seven radicals were present at 10 K after X irradiation with a dose of about 150 kGy. Two different protonation states of the one-electron reduced cytosine cation were observed: an amino-protonated species (R1) and the pristine one-electron reduced species (R2) with zero net charge. Apparently three deprotonated versions of the one-electron oxidized cytosine cation were formed: the amino-deprotonated cation (R3), an N3-deprotonated cation (R4) and an N1-deprotonated cation (R5). Finally, two products formed by net hydrogen addition to the cytosine base were observed: a C5 hydrogen-addition radical (R6) and a C6 hydrogen-addition radical (R7). The crystalline lattice of cytosine hydrochloride is characterized in part by a cytosine base initially protonated at the N3-position, thus forming a cytosine base cation, and in part by an extended network of hydrogen bonding involving the chlorine anions. Proton transfer properties of pristine one-electron oxidation and reduction base products in this lattice are discussed and are suggested as explanations of the unusual multitude of positions for deprotonation of the one-electron oxidized species as well as for the two protonation states of the reduction product observed. The magnetic parameters for the amino-protonated species R1 agree well with those extracted from previous studies of cytosine derivatives in frozen solutions and in various glasses.

Crystallography↗
PubMed1998

Monte Carlo simulation of electron cones used in electron beam therapy.

A Siemens Mevatron KV2 accelerator installed at the Royal Adelaide Hospital employs cylindrical solid-walled electron cones for some electron collimation. The cones being used at present result in treatment fields that do not always conform with the International Electrotechnical Commission (IEC) Standards (particularly at high energies). The aim of this project was to simulate the existing cones using Monte Carlo methods in order to evaluate potential cone modifications required to overcome the field irregularities. Simulations were performed using the EGS4 (Electron Gamma Shower version 4, distribution II) Monte Carlo code installed on a DEC Alpha workstation at the University of South Australia. To rigorously simulate the existing electron cones it was necessary to also simulate various components within the treatment head of the linear accelerator. Results of simulations for existing cones were found to be consistent with experimental data. (obtained from Royal Adelaide Hospital beam quality assurance measurements). Two proposed changes to the cones were then simulated and the effects of these alterations were assessed. This study has shown how treatment head simulation techniques can be used to assess the changes in dose distribution that result from alterations to the treatment head and accessories. Within practical engineering constraints modifications to an existing electron collimation system were proposed and theoretically evaluated.

Biophysical Phenomena↗
PubMed1999

A procedure to prepare cultured cells in suspension for electron probe X-ray microanalysis: application to scanning and transmission electron microscopy.

We describe a simple procedure to prepare cultured cells in suspension to analyse elemental content at the cellular level by electron probe X-ray microanalysis. Cells cultured in suspension were deposited onto polycarbonate tissue, culture plate well inserts, centrifuged at low g, washed to remove the extracellular medium, cryofixed and freeze-dried, and analysed in the scanning mode of a scanning electron microscope. We tested the effect of different washing solutions (150 mM ammonium acetate, 300 mM sucrose, and distilled water) on the elemental content of cultured cells in suspension. The results demonstrated that distilled water was the best washing solution to prepare cultured cells. In addition, the low Na content, high K content and high K/Na ratio of the cells indicated that this procedure, based on the centrifugation at low g followed by cryopreparation, constitutes a satisfactory method to prepare cultured cells in suspension. We also investigated the effects of different accelerating voltages on X-ray signal collection. The results showed that moderate accelerating voltages, i.e. 10-11 kV, should be used to analyse whole cells in the scanning mode of the scanning electron microscope. We show that this method of preparation makes it possible to prepare cryosections of the cultured cells, thus permitting analysis of the elemental content at the subcellular level, i.e. nucleus, cytoplasm and mitochondria, using a scanning transmission electron microscope.

Cell Compartmentation↗
PubMed2000

Electron probe X-ray microanalysis of cultured myogenic C2C12 cells with scanning and scanning transmission electron microscopy.

Heterogeneity of the elemental content of myogenic C2C12 cultured cells was studied by electron probe X-ray microanalysis (EPXMA) with scanning (SEM EPXMA) and scanning transmission electron microscopy (STEM EPXMA). The best plastic substrate for growing cells was Thermanox. For STEM EPXMA, a Formvar film coated with carbon was found to be suitable substrate. The cells examined by scanning transmission electron microscopy showed great heterogeneity in their elemental content in comparison with the cells examined in the scanning electron microscope despite of an almost identical preparation procedure for EPXMA. Nevertheless the K/Na ratios obtained from both methods of EPXMA were very close (4.1 and 4.3). We conclude that the observed discrepancy in the elemental content obtained by the two methods may be due to differences in instrumentation and this must be taken into account when planning a comparative study.

Animals↗
PubMed1996

Contribution of transmission electron microscopy to fine-needle aspiration biopsy diagnosis: comparison of cytology and combined cytology and transmission electron microscopy with final histological diagnosis.

This report evaluates 74 fine-needle aspiration biopsies processed for transmission electron microscopy with subsequent surgical procedure. The specificity of diagnosis obtained by cytology alone was compared to that obtained by cytology and electro microscopy, using histologic diagnosis as the gold standard. When cytology gave a diagnosis of malignancy but could not give tumor category or type, electron microscopy could correctly give both. When cytology could give tumor category but not type, electron microscopy correctly identified type in the majority of cases. When cytology gave tumor category and type, electron microscopy confirmed the diagnosis. Transmission electron microscopy is very helpful when the cytopathologist can diagnose malignancy but cannot give tumor category and/or type. When the cytopathologist is specific in his/her diagnosis, TEM is not as helpful.

Adenocarcinoma↗
PubMed2004

Synthesis and redox behavior of ruthenocene-terminated oligoenes: characteristic and stable two-electron redox system and lower potential shift of the two-electron oxidation wave with elongating conjugation.

Ruthenocene-terminated butadienes and hexatrienes were prepared by the Wittig reaction of 3-ruthenocenyl-2-propenals with ruthenocenylmethylphosphonium salts and the Mukaiyama coupling of the propenals, respectively. Cyclic voltammetry of these complexes indicated that they were involved in a stable two-electron redox process. The oxidation potentials for ruthenocene-terminated oligoenes shifted progressively to lower potential with the increasing CH==CH units as follows: Rc--Rc (0.32 V)>RcCH==CHRc (+0.09 V)>Rc(CH==CH)(2)Rc (-0.06 V)>Rc(CH==CH)(3)Rc (-0.07 V), (Rc=ruthenocene). The tendency is in remarkable contrast to that in the successive one-electron redox process. These complexes were chemically oxidized to give stable crystalline solids, whose structures were confirmed by NMR spectroscopy and X-ray analysis to be oligoene analogues of a bis(fulvene) complex, for example, [(eta(5)-C(5)Me(5))Ru[mu(2)-eta(6):eta(6)-C(5)H(4)CH(CH==CH)(n)CHC(5)H(4)]Ru(eta(5)-C(5)Me(5))](2+) (n=1 or 2). The DFT calculation of the two-electron-oxidized species reproduced well the fulvene-complex structure for the ruthenocene moieties. Since both the neutral and oxidized species are stable and chemically reversible, this redox system may be serviceable as a two-electron version of the ferrocene one-electron redox system.

Journal Article↗
PubMed2003

Comparison of electron density properties in frozen and relaxed electronic distributions.

Two kinds of electron densities for several small molecules (H(2), FH, CH(3)CH(3), CH(3)NH(2), CH(3)OH, and CH(3)F) have been generated for a wide range of bond distances. The first one, as the sum of the electron density of the isolated fragments, and the second one by optimizing the electron density at each given geometrical disposition. A number of properties of this two electronic distributions have been compared (position of the bond critical points, electron density, Laplacian, curvatures, and local energies). The differences, associated to the bond formation, are found to be very important for most of the cases.

Journal Article↗
PubMed1984

Intracellular parasite killing induced by electron carriers. I. Effect of electron carriers on intracellular Leishmania spp. in macrophages from different genetic backgrounds.

Mouse peritoneal macrophages were infected with Leishmania parasites from different species, then exposed to the electron carriers methylene blue (MB), toluidine blue O (TB), phenazine methosulfate (PMS) and crystal violet (CV). This led to killing of the intracellular parasites with no harm to the macrophages. On a molar basis, the potency of the electron carriers decreased in the following order: CV, TB, MB and PMS. MB and TB were more active against intracellular compared to free parasites, suggesting that the macrophages themselves might play a role in the observed anti-parasite toxicity. Intracellular killing could be achieved by a short pulse (30 min) of electron carrier. No difference could be detected between macrophages from different mouse strains as regards their capacity to kill intracellular parasites upon incubation with electron carriers. When macrophages from the L. major susceptible ('non-healer') BALB/c strain were infected with either L. enriettii (which is nonpathogenic to mice) or L. major, then exposed to an activating, lymphokine-rich supernatant, destruction of only L. enriettii was achieved, whereas L. major survived intracellularly. Incubation with MB, however, led to intracellular destruction of both parasites. Other Leishmania species could also be killed irrespective of the genetic background of the macrophages. These observations suggest that the triggering events in electron carrier- and lymphokine-mediated intracellular parasite killing are different.

Animals↗
PubMed2003

Comparison of simulation methods for electronic structure calculations with experimental electron energy-loss spectra.

The electronic structure of hexagonal GaN is studied using two simulation techniques in order to develop a method to interpret the fine-structure of an experimental nitrogen K-edge electron energy loss spectrum obtained using a scanning transmission electron microscope. The application of these simulation methods to the bulk spectrum is a necessary first step in developing a fundamental understanding of the effect of changes in the electronic structure on the properties of defects. It is found here that both of the techniques used, multiple scattering (MS) and density functional theory (DFT), produce excellent agreement with the experimental bulk spectrum. The MS method is limited in accuracy but efficient in time, while the DFT method is more accurate but time consuming. Through the combination of these methods, experimental energy loss spectra can be readily understood, and a means to unravel the complexities of the electronic structure can be determined.

Journal Article↗
PubMed1993

Binding and electron transfer reactions between methanol dehydrogenase and its physiologic electron acceptor cytochrome c-551i: a kinetic and thermodynamic analysis.

The quinoprotein methanol dehydrogenase and cytochrome c-551i form a physiologic complex in which electrons are transferred from pyrroloquinoline quinone to heme. The reoxidation of methanol dehydrogenase by the cytochrome was studied by stopped-flow spectroscopy. The rate constant for the electron transfer reaction and the dissociation constant for complex formation were each determined at temperatures ranging from 20 to 50 degrees C. The electron transfer rates varied from 1.4 to 4.6 s-1. Analysis of the electron transfer reaction by Marcus theory yielded values of 1.9 eV for the reorganizational energy and 0.071 cm-1 for the electronic coupling and predicted a theoretical distance between redox centers of 15 A. Kinetically determined dissociation constants correlated well with a Kd of 375 microM which was determined in a direct ultrafiltration binding assay. Thermodynamic analysis of the dissociation constants indicated the importance of the hydrophobic effect in complex formation.

Alcohol Oxidoreductases↗
PubMed2002

Electronic structures of electron-rich octahedrally condensed transition-metal chalcogenide clusters.

The electronic structures of some electron-rich octahedrally condensed transition-metal chalcogenide clusters are analyzed with the aid of extended Hückel and density functional molecular orbital calculations. A simple orbital approach is developed to analyze the electron counts of these clusters, which do not obey any existing electron-counting rules. Different electron counts are allowed, depending upon the nature of the metal. Optimal counts are discussed. Metal-metal bonding is generally weak in these species. Consequently, their structural arrangements are mainly governed by metal-ligand interactions.

Journal Article↗