2,6-Dichloro-phenol indophenol prevents switch-over of electrons between the cyanide-sensitive and -insensitive pathway of the mitochondrial electron transport chain in the presence of inhibitors

To evolve a simple oxygen electrode-based method to estimate alternative respiration, one needs to develop a procedure to prevent switch-over of electrons to either pathway upon inhibition by cyanide or salicylhydroxamic acid. It was hypothesized that the inclusion of appropriate electron acceptor, possessing redox potential close to one of the electron transport carriers in between ubiquinone (branch point) and cytochrome a-a3, should be able to stop switch-over of electrons to either pathway by working as an electron sink. To test the hypothesis, 2,6-dichloro-phenol indophenol (DCPIP; redox potential +0.217 V), an artificial electron acceptor having a redox potential quite similar to the site near cytochrome c1 (redox potential +0.22 V) on the cyanide-sensitive pathway, was used with isolated mitochondria and leaf discs in the absence and presence of inhibitors (potassium cyanide, antimycin A, and salicylhydroxamic acid). Polarographic data confirmed electron acceptance by DCPIP only from the inhibited (by cyanide or salicylhydroxamic acid) mitochondrial electron transport chain, hence preventing switch-over of electrons between the cyanide-sensitive and cyanide-insensitive pathway of respiration. Results with antimycin A and reduction status of DCPIP further confirmed electron acceptance by DCPIP from the mitochondrial electron transport chain. Possible implications of the results have been discussed.     

Investigation of the interaction of the water oxidising manganese complex of photosystem II with the aqueous solvent environment

Interaction of the water oxidising manganese complex of photosystem II with the aqueous environment has been investigated using electron paramagnetic resonance spectroscopy and electron spin echo envelope modulation spectroscopy to detect interaction of [2H]methanol with the complex in the S2 state. The experiments show that the classical S2 multiline signal is associated with a manganese environment which is not exposed to the aqueous medium. An electron paramagnetic resonance spectroscopy signal, also induced by 200 K illumination, showing 2H modulation by methanol in the medium and a modified multiline electron paramagnetic resonance spectroscopy signal formed in parallel to it, are suggested to be associated with a second manganese environment exposed to the medium.     

Regulation of Photosystem Composition in the Cyanobacterial Photosynthetic System: the Regulation Occurs in Response to the Redox State of the Electron Pool Located between the Two Photosystems

Regulation of electron transport composition was studied withSynechocystis (Aphanocapsa) PCC 6714 grown under various trophicconditions. Photosystem (PS) composition, PS I/IIratio, wasused as the index for the composition of the electron transportsystem. Special attention was paid to the relationship betweenchanges in the PS I/II ratio and features of electron transport.Results indicated that (1) the change of composition of theelectron transport system is induced not only by the light conditionsbut also by changes in the electron influx and efflux. (2) Thechange occurs so as to relieve the imbalance between the electroninflux and the efflux, caused by changes in the conditions forthe electron transport, and (3) the redox state of plastoquinonepool is probably related to the primary stimulus of the regulation. (Received August 14, 1986; Accepted December 16, 1986)     

Comparison of three electron microscopy techniques for the detection of human rotaviruses

Rotavirus detection by direct electron microscopy was compared with direct and indirect immune electron microscopy techniques. The latter two approaches permitted the enumeration of 25 and 103 times more rotaviruses respectively, than direct electron microscopy. Also, 70% and 90% of the virus particles were aggregated by direct and indirect immune electron microscopy techniques respectively, thus facilitating their detection.     

An Analysis of the Mechanism of the Low-wave Phenomenon of Chlorophyll Fluorescence

The low-wave phenomenon, i.e., the transient drop of yield of modulated chlorophyll fluorescence shortly after application of a pulse of saturating light, was investigated in intact leaves of tobacco and Camellia by measuring fluorescence, CO(2) assimilation and absorption at 830 nm simultaneously. Limitations on linear electron flow, due to low electron acceptor levels that were induced by low CO(2), induced the low waves of chlorophyll fluorescence. Low-wave amplitudes obtained under different CO(2) concentrations and photon-flux densities yielded single-peak curves when plotted as functions of fluorescence parameters such as PhiPS II (quantum yield of Photosystem II) and qN (coefficient of non-photochemical quenching), suggesting that low-wave formation depends on the redox state of the electron transport chain. Low waves paralleled redox changes of P700, the reaction center of Photosystem I (PS I), and an additional electron flow through PS I was detected during the application of saturating pulses that induced low-waves. It is suggested that low waves of chlorophyll fluorescence are induced by increased non-photochemical quenching, as a result of the formation of a trans-thylakoid proton gradient due to cyclic electron flow around PS I.     

Regulation of the photosynthetic electron transport chain

The regulation of electron transport between photosystems II and I was investigated in the plant Silene dioica L. by means of measurement of the kinetics of reduction of P₇₀₀ following a light-to-dark transition. It was found that, in this species, the rate constant for P₇₀₀ reduction is sensitive to light intensity and to the availability of CO₂. The results indicated that at 25 °C the rate of electron transport is down-regulated by approximately 40–50% relative to the maximum rate achievable in saturating CO₂ and that this down-regulation can be explained by regulation of the electron transport chain itself. Measurements of the temperature sensitivity of this rate constant indicated that there is a switch in the rate-limiting step that controls electron transport at around 20 °C: at higher temperatures, CO₂ availability is limiting; at lower temperatures some other process regulates electron transport, possibly a diffusion step within the electron transport chain itself. Regulation of electron transport also occurred in response to drought stress and sucrose feeding. Measurements of non-photochemical quenching of chlorophyll fluorescence did not support the idea that electron transport is regulated by the pH gradient across the thylakoid membrane, and the possibility is discussed that the redox potential of a stromal component may regulate electron transport. Received: 4 March 1999 / Accepted: 25 May 1999     

Influence of the plasma density and heating power on the intensity of electron cyclotron emission in the L-2M stellarator

Results are presented from experiments on studying the plasma behavior in the L-2M stellarator in regimes with a high power deposition in electrons during electron cyclotron heating at the second harmonic of the electron gyrofrequency (X mode) at heating powers of P _in=120–400 kW and average plasma densities from n _e≤3×10¹⁹ to 0.3×10¹⁹ m^?3. It is shown that, as the plasma density decreases and the heating power increases, the electron cyclotron emission spectrum is modified; this may be attributed to a deviation of the electron energy distribution from a Maxwellian and the generation of suprathermal electrons. At low plasma densities, the emission intensity at the second harmonic of the electron gyrofrequency increases, whereas the plasma energy measured by diamagnetic diagnostics does not increase. This poses the question of the correctness of determining the plasma electron temperature by electron cyclotron emission diagnostics under these conditions.     

Studies on the Mutagenic Effect of the Chromosome by 5 MeV Electron

In this experiment, electron and y-ray-radiation were used to irradiate dry seeds of Vicia faba. Experimental results show that electron just as affective as γ-ray has significant mutagenic effect on cells. In the range of the dose, the frequency of chromosomal aberrations on the root tip cells, there are singnificantly dose-effect. But the relationship between the dose and frequency of aberrations is close to straight line and redplication. An analysis from the type of chromosomal aberrations by electron also leads to different results, in which there are more bridges and rings by electron than by γ-ray. Therefore, electron possibly have stronger two hit aberrations, and the frequency of aberration increased in proporti on with the square of dose.     

细胞固定化方法制备微藻光电极的研究

通过将微藻细胞固定在平面多孔碳纸上,制备微藻光电极,并在三电极体系电解液中加入电子介体进行测试,可产生与光照同步的光电流响应。考察了不同固定化方法、不同微藻及不同电子介体的光电流响应,结果表明硅溶胶-凝胶法制备的光电极光电流响应最佳,且对于亚心形四爿藻、金藻、莱茵衣藻、蛋白核小球藻、聚球藻等 5 种微藻都适用,表明该制备方法对不同微藻具有较好的通用性。电子介体的研究表明苯醌及其衍生物由于氧还电位较高,具有较好的阳极光电流响应特性,而甲基紫精氧还电位较低,具有较好的阴极光电流响应。     

Bypasses of the antimycin a block of mitochondrial electron transport in relation to ubisemiquinone function

Two different bypasses around the antimycin block of electron transport from succinate to cytochrome c via the ubiquinol-cytochrome c oxidoreductase of intact rat liver mitochondria were analyzed, one promoted by N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and the other by 2,6-dichlorophenolindophenol (DCIP). Both bypasses are inhibited by myxothiazol, which blocks electron flow from ubiquinol to the Rieske iron-sulfur center, and by 2-hydroxy-3-undecyl-1,4-naphthoquinone, which inhibits electron flow from the iron-sulfur center to cytochrome c1. In the bypass promoted by TMPD its oxidized form (Wurster's blue) acts as an electron acceptor from some reduced component prior to the antimycin block, which by exclusion of other possibilities is ubisemiquinone. In the DCIP bypass its reduced form acts as an electron donor, by reducing ubisemiquinone to ubiquinol; reduced DCIP is regenerated again at the expense of either succinate or ascorbate. The observations described are consistent with and support current models of the Q cycle. Bypasses promoted by artificial electron carriers provide an independent approach to analysis of electron flow through ubiquinol-cytochrome c oxidoreductase.     

Electron transfer between globular proteins. Dependence of the rate of transfer on distance

Based on the assumption that electron transfer between globular proteins occurs by a collective excitation of polaron type, the dependence of the rate of this process on the distance between the donor and acceptor centers with regard to their detailed electron structure was calculated. The electron structure of the heme was calculated by the quantum-chemical MNDO-PM3 method. The results were compared with experimental data on interprotein and intraglobular electron transfer. It is shown that, in the framework of this model, the electron transfer is not exponential and does not require a particular transfer pathway since the whole protein macromolecule is involved in the formation of the electron excited state.     

The use of backscattered electrons in analytical electron microscopy for the measurement of the mass of individual rat blood platelets

Summary The backscattered electron signal, generated in individual cells, has been used to measure the dry mass of these cells. Absolute mass values were obtained by comparing the backscattered electron signals of cells to the signals of polystyrene-latex spheres of known mass. The technique was carried out in an automated analytical scanning transmission electron microscope and applied to rat blood platelets.The resulting mass distributions agreed well with the distribution measured with a method that uses the transmitted electron signal by means of densitometric analysis of electrographs. Also the range of masses was in agreement with values deduced from data in the literature.The fully automated technique has the advantage that it is direct, fast, and that thicker specimens can be measured than is possible using the transmitted electron signal. The method is intended for use in combination with quantitative electron probe X-ray microanalysis and is then able to produce elemental mass fractions of biological specimens at the subcellular level.In honour of Prof. van Duijn     

The use of backscattered electrons in analytical electron microscopy for the measurement of the mass of individual rat blood platelets

The backscattered electron signal, generated in individual cells, has been used to measure the dry mass of these cells. Absolute mass values were obtained by comparing the backscattered electron signals of cells to the signals of polystyrene-latex spheres of known mass. The technique was carried out in an automated analytical scanning transmission electron microscope and applied to rat blood platelets. The resulting mass distributions agreed well with the distribution measured with a method that uses the transmitted electron signal by means of densitometric analysis of electrographs. Also the range of masses was in agreement with values deduced from data in the literature. The fully automated technique has the advantage that it is direct, fast, and that thicker specimens can be measured than is possible using the transmitted electron signal. The method is intended for use in combination with quantitative electron probe X-ray microanalysis and is then able to produce elemental mass fractions of biological specimens at the subcellular level.     

青春型双歧杆菌超微结构的观察

本文主要对青春型双歧杆菌(Bif.adolescentis)的超微结构进行了观察。发现细胞壁外有一层厚薄不一的糖被,细胞壁有双层结构即外界膜和内界膜。而有明显分叉的菌体则见不到糖被并可见菌体中心出现大量的糖原颗粒、空泡或液泡,这提示分叉的形成系与环境的不利有关。     

Ultrastructure of the Spermatozoon of Avitellina centripunctata(Cestoda,Cyclophyllidea), a Parasite of the Small Intestine of Cattle in Senegal

The Avitellina centripunctataspermatozoon is filiform, tapered at both ends and lacks mitochondria. The anterior extremity exhibits an apical cone and a crested–like body 150–200 nm thick. The axoneme is surrounded by a fine layer of lucent cytoplasm and a sheath of electron–dense material. The cytoplasm is slightly electron–dense at the anterior tip of the apical cone and in region IV of the spermatozoon. Over the rest of the gamete it is subdivided into numerous electron–lucent compartments by irregularly spaced walls. The nucleus is electron–dense. It interposes itself between the cortical microtubules which are all electron–dense centred and spiralized along their whole length. An apical zone containing spiralized microtubules, cortical microtubules which are all electron–dense centred and stop before reaching the posterior extremity of the nucleus, as well as the subdivision into cavities by intracytoplasmic proteinaceous material, have never been described before in a cestod. Moreover, the crested–like body of Avitellina centripunctatais the thickest of those which have been described to date in the cestods.     

Metal compound intensification of the electron-density of diaminobenzidine

Diaminobenzidine (DAB), commonly used in immunocytochemistry as the substrate for peroxidase, has a low electron density. DAB has a known affinity for the salts of some metals and therefore an examination of the ability of six metal compounds (including osmium tetroxide) to increase the electron density associated with DAB deposits has been undertaken. Ultra-thin sections of unosmicated rat pituitary gland, embedded in L. R. White resin, were immunostained by a hapten sandwich immunoperoxidase method, using antibodies to ACTH and TSH. The unintensified electron density of the DAB polymer reaction product on the specific endocrine granules was compared with the electron density resulting from the use of each of the six metal compounds. Lead and silver nitrate gave unsatisfactory results, while phosphotungstic acid and uranyl acetate produced a limited increase in specific electron density under the conditions used. Gold chloride was found to give the highest electron density to the specific endocrine granules, followed closely by osmium tetroxide. Background staining was greater when osmium was used. We conclude that several metal compounds may be used to intensify the electron density of DAB, but of the ones tested, gold chloride, which is safer, more stable, and cheaper than osmium tetroxide, was clearly the best. This approach not only increases the electron density of the DAB reaction product, but allows of the possibility of quantitation using energy dispersive X-ray analysis.     

A Quantitative Estimation of the Uptake of Two New Electron Stains by the Cytoplasmic Membrane of Ram Sperm

From microdensitometer measurements on electron micrographs of sectioned sperm heads it has been found that the electron stains, triiodobenzoyl chloride, and triiodophenylisocyanate, increase the image contrast of the cell membrane above its immediate background by about 40 per cent and 70 per cent respectively, while the nucleus remains unstained. Assumptions based on current electron scattering theory have been used to deduce the uptake by weight of the stains in terms of the density of the nucleus, which was estimated from complementary measurements made with the interference microscope and electron microscope. The uptake of the stains was found to be about 7 per cent and 12 per cent by weight respectively. It is suggested that the method used in this work could be applied generally for the density measurement of cell structures unresolved by the light microscope.     

The effect of inhibitors on the electron flow triggering photo-phobic reactions in cyanophyceae

1. Since photo-phobic reactions in the blue green alga Phormidium uncinatum seem to be triggered by changes of electron flow rates into or out of an electron pool situated in the electron transport chain between photosystem II and I, the effect of inhibitors affecting the electron transport chain has been studied.
2. Dose response curves of the phobic reaction have been measured by varying the trap energy in double beam light trap experiments with constant pairs of monochromatic light. From these dose response curves the effects of the inhibitors on both types of phobic reactions, i.e. exit reactions and entrance reactions, have been calculated.
3. Dibromothymoquinone (DBMIB) inhibits the electron transport between the electron pool and photosystem I by preventing the reoxidation of plastoquinone. The phobic entrance reaction, which results in an emptying of the light trap, is triggered by changes in the electron flow out of the pool; thus it is more effected by DBMIB than the exit reaction, which is mediated by the electron transport into the pool.
4. The phobic exit reaction, which results in accumulations in the light trap, is triggered by changes in the electron flow into the electron pool via photosystem II. 3-[3,4-dichlorophenyl]-1,1-dimethylurea (DCMU) inhibits the electron transport near photosystem II; thus it affects the exit reaction more than the entrance reaction.

     

X-Ray Diffraction of Myelin Membrane: II. Determination of the Phase Angles of the Frog Sciatic Nerve by Heavy Atom Labeling and Calculation of the Electron Density Distribution of the Membrane

The phase signs of the five main X-ray reflections from normal frog sciatic nerve have been determined as all positive using a technique of labeling with very small amounts of heavy metal. The changes in intensity of the individual reflections were studied as a function of uptake of metal label by the membrane. The possible localization of the metal label was decided from computer-analogue studies and from Patterson calculations. These phases are different from those determined by previous workers using techniques of trial of the best set of phases, or a step model, to give the best fit of the combined intensity data of normal and swollen myelin membranes. The electron density map has been calculated using eight reflections and their experimentally determined phases. The map shows an inner low electron density region which is different from that shown by earlier calculations. The center of the low electron density region shows a small region of increased electron density. However, without fixing absolute electron density levels in the map, it is not yet possible to allocate regions of low electron density to pure lipid or lipoprotein. The map shows the two sides of the membranes to be different in molecular structure without significant water spaces between the membranes.     

Trapping of electrons and acceleration of the electron bunch in a wake wave

The process of electron trapping by a wake wave excited by a laser pulse in a plasma channel in the case where the electron bunches are injected into the vicinity of the maximum of the wakefield potential at a velocity lower than the wave phase velocity is considered. The mechanism for the formation of a compact electron bunch in the trapping region when only the electrons of the injected bunch that are trapped in the focusing phase mainly undergo the subsequent acceleration in the wakefield is analyzed. The influence of the spatial dimensions of the injected bunch and its energy spread on the length of the trapped electron bunch and the fraction of trapped electrons is studied analytically and numerically. For electron bunches with different ratios of their spatial dimensions to the characteristic dimensions of the wake wave, the influence of the injection energy on the parameters of the high-energy electron bunch trapped and accelerated in the wake-field is studied.