Visualizing gas molecules interacting with supported nanoparticulate catalysts at reaction conditions

Understanding how molecules can restructure the surfaces of heterogeneous catalysts under reaction conditions requires methods that can visualize atoms in real space and time. We applied a newly developed aberration-corrected environmental transmission electron microscopy to show that adsorbed carbon monoxide (CO) molecules caused the {100} facets of a gold nanoparticle to reconstruct during CO oxidation at room temperature. The CO molecules adsorbed at the on-top sites of gold atoms in the reconstructed surface, and the energetic favorability of this reconstructed structure was confirmed by ab initio calculations and image simulations. This atomic-scale visualizing method can be applied to help elucidate reaction mechanisms in heterogeneous catalysis.     

Membrane recycling: vesiculation of the amoeba contractile vacuole at systole

Ultrastructural data on the protozoan Amoeba proteus support a model of membrane recycling. At systole the amoeba contractile vacuole fuses with the cell surface and expels its contents. Observations by electron microscopy indicate that, as the vacuole empties, its bounding membrane transforms into tiny (35 nanometers in diameter) vesicles, identical to the vesicles that segregate fluid and contribute to the diastolic vacuole.     

黑根霉菌孢囊孢子形成的电镜观察

电镜观察发现,黑根霉菌的孢囊孢子是以原生质割裂的方式形成。在原生质割裂初期,细胞核核膜上形成了形状不同的泡囊,该孢囊的产生与割裂泡的产生可能密切相关。大量的割裂泡通过在细胞核外的有规律排列和相互间的接合,从而将孢囊的原生质割裂开来,并形成大量的无壁新细胞,该细胞的质膜来源于割裂泡的外膜。随着细胞壁的出现,这些无壁的细胞最终发育成为孢囊孢子。观察还发现,孢囊的囊轴与原生质割裂是同步的。     

Structure of biological membranes

The combined x-ray diffraction and electron microscopic examination of myelin has provided reasonable, but not conclusive, support for its structure as a basically bimolecular leaflet of phospholipid that is partially interspersed with protein. But there is very little basis for extending this concept to biological membranes in general. There is no adequate experimental support for the specific orientation of phospholipids as proposed in the unit membrane theory or for the proposed polar nature of protein-lipid bonds, even in myelin. Membranes differ widely in chemical composition, metabolism, function, enzymatic composition, and even in their electron microscopic image. The only similarity is their general resemblance in electron micrographs, but, until more is known about the chemistry of electron microscopy, this evidence cannot be interpreted with confidence. One positive conclusion to which I have come is that much more chemical evidence must, and can, be obtained. Techniques for the isolation of membranes are improving and protein and lipid chemistry are now highly refined arts. Quantitative analysis of many different membranes is possible and the data can be related in some instances, notably bacterial plasma membranes, to calculations of surface area. Chemical and physical changes induced in membranes of widely different lipid composition by the preparatory procedures of electron microscopy can be determined directly and correlated with the electron microscopic image. Model systems can be assembled whose compositions closely resemble those of biological membranes. Membranes can be disassociated into subunits whose properties can be studied. In particular, x-ray diffraction analysis and electron microscopy by negative staining of reaggregates of lipoproteins isolated from membranes would be very informative. Perhaps most important, the problem of membrane structure must be considered in relation to the problems of membrane function and membrane biosynthesis.     

Ultrastructural characteristics of absorption of immunoglobulins in the small intestine of newborn piglets

It is established by electron microscopy that absorption of immunoglobulins occurs by the formation of endocytotic invaginations and vesicles of the apical membrane of small intestine enterocytes of piglets in the first hours and days of life. The process of absorption of substances taken in with colostrum, including the transport of intact immunoglobulin, is characterized.     

Transport studies in bacterial membrane vesicles

The use of bacterial membrane vesicles as an experimental system for the study of active transport has been discussed. Vesicles are prepared from osmotically sensitized bacteria, and consist of osmotically intact, membranebound sacs without internal structure. They retain litle or no cytoplasm. Under appropriate conditions, these vesicles catalyze the transport of a variety of solutes at rates which are comparable, in many cases, to those of intact cells. Two general types of transport systems have been elucidated in the vesicle system: (i) group translocation systems which catalyze vectorial covalent reactions; and (ii) respirationlinked transport systems that catalyze the active transport of a whole range of metabolites against an electrochemical or osmotic gradient. In E. coli membrane vesicles, the respiration-linked transport systems are coupled primarily to the oxidation of (D)-lactate to pyruvate, catalyzed by a flavin-linked, membrane-bound (D)-lactate dehydrogenase which has been purified to homogeneity. Electrons derived from (D)-lactate or certain artificial electron donors are transferred to oxygen by means of a membrane-bound respiratory chain, and respiration is coupled to active transport within a segment of the respiratory chain between the primary dehydrogenase and cytochrome. b(l). The great majority of the individual membrane vesicles in the population catalyze active transport, and the generation or hydtolysis of ATP is not involved. Under anaerobic conditions, fumarate or nitrate can be utilized in place of oxygen as terminal electron acceptors. With the exception that (D)-lactate is not always the most effective electron donor for active transport, vesicles prepared from a number of other organisms catalyze transport in a similar manner. Fluorescent dansylgalactosides are useful molecular probes of active transport in the vesicle system. These compounds are competitive inhibitors of beta-galactoside transport, but are not transported themselves. Fluorescence studies indicate that the lac carrier protein constitutes approximately 3 to 6 percent of the total membrane protein, and that it is not accessible to the external medium unless the membrane is "energized." Thus, energy is coupled to one of the initial steps in the transport process. Studies with a photoaffinity-labeled galactoside provide independent support for this conclusion. When membrane vesicles prepared from a (D)-lactate dehydrogenase mutant of E. coli are treated with (D)-lactate dehydrogenase, the enzyme binds to the vesicles and they regain the capacity to catalyze (D)-lactate oxidation and (D)-lactate-dependent active transport. The maximal specific transport activity obtained in the reconstituted system is similar in magnitude to that of wildtype vesicles. Titration studies with dansylgalactoside demonstrate that there is at least a seven- to eightfold excess of lac carrier protein relative to (D)-lactate dehydrogenase. Evidence is presented indicating that the enzyme is bound to the inner surface of native membrane vesicles and to the outer surface of reconstituted vesicles, and that the flavin coenzyme moiety is critically involved in binding. Possible mechanisms of respirationlinked active transport are discussed.     

Polymer vesicles

Vesicles are microscopic sacs that enclose a volume with a molecularly thin membrane. The membranes are generally self-directed assemblies of amphiphilic molecules with a dual hydrophilic-hydrophobic character. Biological amphiphiles form vesicles central to cell function and are principally lipids of molecular weight less than 1 kilodalton. Block copolymers that mimic lipid amphiphilicity can also self-assemble into vesicles in dilute solution, but polymer molecular weights can be orders of magnitude greater than those of lipids. Structural features of vesicles, as well as properties including stability, fluidity, and intermembrane dynamics, are greatly influenced by characteristics of the polymers. Future applications of polymer vesicles will rely on exploiting unique property-performance relations, but results to date already underscore the fact that biologically derived vesicles are but a small subset of what is physically and chemically possible.     

云南烟草丛枝症病害研究 II细胞的超微病变

超薄切片观察云南烟草丛枝症病害的病叶组织,并抽提试验材料的总核酸电泳检测,结果表明：病组织中检测到与烟草丛枝症病害相关的低分子量ＲＮＡ,切片中未观察到病毒粒子,薄壁细胞中发现细胞膜系统的畸变：质膜体（ｐｌａｍａｌｅｍｍａｓｏｍｅ）和双层膜泡囊（ｄｏｕｂｌｅｍｅｍｂｒａｎｏｕｓｖｅｓｉｃｌｅｓ）．质膜体由细胞质膜或液泡膜伸入空泡形成,直径约１０００～２０００ｎｍ,结构类似于类病毒侵染寄主形成的旁壁体．双层膜泡囊是含纤维状物内含物的泡囊,直径约１００～２００ｎｍ,结构类似于某些病毒侵染寄主形成的细胞质泡囊（ｃｙｔｏｐｌａｓｍｉｃｖｅｓｉｃｌｅｓ）和植原体（ｐｈｙｔｏｐｌａｓｍａｓ）,但因其广泛分布于寄主细胞中,不能认为是植原体．文献显示这些病变是类病毒和某些病毒侵染的特征,初步认为云南烟草丛枝症病害可能是病毒病害,发病早期细胞内出现小分子核酸侵染的细胞病变特征,此与莫笑晗等发现病株体内含有大量低分子量ＲＮＡ可能有密切关系．     

毛赤杨根瘤内生菌的超微结构研究

通过光学和电子显微镜对5~10月生长季节内的毛赤杨(Alnus hirsute)固氮根瘤进行了研究。超微结构研究结果表明其根瘤有明显季节变化。瘤内生菌表现为2种形式:有分枝且有隔菌丝(0.4~0.8μm)及生长于母体菌丝顶端泡囊(1.5~3.0μm)。毛赤杨根瘤内生菌超微结构与其它赤杨根瘤内生菌相似。     

云南烟草丛枝症病害研究Ⅲ细胞的超微病变

 超薄切片观察云南烟草丛枝症病害的病叶组织,并抽提试验材料的总核酸电泳检测,结果表明:病组织中检测到与烟草丛枝症病害相关的低分子量RNA,切片中未观察到病毒粒子,薄壁细胞中发现细胞膜系统的畸变:质膜体(plamalemmasome)和双层膜泡囊(double membranous vesicles).质膜体由细胞质膜或液泡膜伸入空泡形成,直径约1000～2000nm,结构类似于类病毒侵染寄主形成的旁壁体.双层膜泡囊是含纤维状物内含物的泡囊,直径约100～200nm,结构类似于某些病毒侵染寄主形成的细胞质泡囊(cytoplasmic vesicles)和植原体(phytoplasmas),但因其广泛分布于寄主细胞中,不能认为是植原体.文献显示这些病变是类病毒和某些病毒侵染的特征,初步认为云南烟草丛枝症病害可能是病毒病害,发病早期细胞内出现小分子核酸侵染的细胞病变特征,此与莫笑晗等发现病株体内含有大量低分子量RNA可能有密切关系.     

Molecular microscopy: fundamental limitations

On the basis of estimates of molecular damage caused by the observation process, it is concluded that molecular microscopy of biological molecules in which the individual atoms are resolved is impossible with an electron or x-ray microscope. Microscopes that use low-energy helium atoms or neutrons as illuminants may be capable of serving as ultimate biomolecular microscopes.     

DNA structure: evidence from electron microscopy

The contour lengths of phiX174 DNA duplex and RNA-DNA hybrid molecules were measured by several commonly used electron microscopic techniques. The countour length of the hybrid molecules corresponds to a rise of 2.5 to 2.6 angstroms per base pair, as expected for the A conformation, while the length of phiX174 duplex DNA similarly measured corresponds to a 2.9-angstrom rise, very different from 3.4 angstroms of the classic B form. Thus any chromatin structure parameter based on electron microscopy and a rise of 3.4 angstroms must be reappraised. The possibility that DNA in dilute solution also has a rise of 2.9 angstroms and a screw of 10.5 base pairs per turn is discussed.     

The fluorescent toolbox for assessing protein location and function

Advances in molecular biology, organic chemistry, and materials science have recently created several new classes of fluorescent probes for imaging in cell biology. Here we review the characteristic benefits and limitations of fluorescent probes to study proteins. The focus is on protein detection in live versus fixed cells: determination of protein expression, localization, activity state, and the possibility for combination of fluorescent light microscopy with electron microscopy. Small organic fluorescent dyes, nanocrystals ("quantum dots"), autofluorescent proteins, small genetic encoded tags that can be complexed with fluorochromes, and combinations of these probes are highlighted.     

Selective solubilization of a protein component of the red cell membrane

Approximately 20 percent of the membrane-bound protein of erythrocyte ghosts can be solubilized and obtained free of other membrane components by dialysis against adenosine triphosphate and 2-mercaptoethanol. This protein forms one major band on polyacrylamide gels and a single boundary in free-boundary electrophoresis, and it undergoes polymerization in the presence of divalent cations to form coiled filaments visible by electron microscopy. Antibodies to this membrane protein react specifically with red blood cells or their membrane ghosts but do not react with serum, erythrocyte cytoplasm, or other blood cells. The functional role of this protein is unknown, but it appears to be involved in maintaiining the structure of the red cell membrane. We suggest that this protein be called Spectrin since it is obtained from membrane ghosts.     

A small gold-conjugated antibody label: improved resolution for electron microscopy

A general method has been developed to make the smallest gold-conjugated antibody label yet developed for electron microscopy. It should have wide application in domainal mapping of single molecules or in pinpointing specific molecules, sites, or sequences in supramolecular complexes. It permits electron microscopic visualization of single antigen-binding antibody fragments (Fab') by covalently linking an 11-atom gold cluster to a specific residue on each Fab' such that the antigenic specificity and capacity are preserved. The distance of the gold cluster from the antigen is a maximum of 5.0 nanometers when the undecagold-Fab' probe is used as an immunolabel.     

微小泰泽球虫大配子发育与受精的超微结构

采用纯种微小泰泽球虫卵囊,人工感染四日龄雏鹅,定时剖杀,取小肠组织进行超薄切片,在透射电镜下观察微小泰泽球虫大配子体的发育与大、小配子的受精过程。大配子体由第二代裂殖子转变而来,在带虫空泡内发育。早期大配子体细胞核的浅层和周围均有多膜空泡分布。在大配子体的表面观察到了正待逸出的电子半透明空泡。成囊颗粒Ⅰ和Ⅱ先后出现,两者在分布、结构、大小及功能上均有明显不同。受精发生在卵囊壁形成之前。小配子的核和鞭毛均进入大配子,随后,小配子的核进入大配子的细胞核。没有观察到小配子鞭毛进入大配子的细胞核。     

Uptake and binding of uranyl ions by barley roots

After undergoing the processing for electron microscopy, bound uranyl ions are revealed as characteristic electron-opaque crystals. Meristematic walls and associated vesicles become heavily labeled, while pinocytotic accumulation into vacuoles seems probable in cap cells and those just behind the meristem. The endodermal Casparian strip and suberinized lamella are effective barriers to the passage of uranyl ions.     

鸭肝炎病毒形态及接种鸡胚引起的病理变化观察

本文研究应用免疫电镜技术观察DHV形态,并对DHV接种鸡胚引起的病理变化进行观察。 DHV颗粒为球形,无囊膜,直径约为15～20毫微米。 将DHV接种10天龄鸡胚,接种后于一定的时间间隙,直至鸡胚死亡,取鸡胚的肝和脑分别制样,用光学显微镜和电子显微镜观察其病理变化。在光镜下,可见肝窦淋巴细胞浸润,肝细胞变性和坏死,肝脏充血出血,大脑脑软膜淋巴细胞浸润和大脑毛细血管充血。肝脏的电镜检查,可见肝细胞间隙有很多泡囊,肝细胞胞浆出现电子密度很高的颗粒状物和空泡,核固缩,最后,核膜皱曲和破裂,细胞膜裂开,细胞器减少或消失。脑的电镜观察,可见脑神经细胞的内质网扩张形成小圆泡,核膜皱曲和破裂。细胞膜也破裂,细胞器溢出。 在肝组织的狄斯隙中可见病毒样颗粒,在靠近细胞膜的胞浆中发现病毒样颗粒被包在由膜围成的泡囊中。     

Double nuclear magnetic resonance observation of electron exchange between ferri- and ferrocytochrome c

Cyanide-inhibited electron exchange between ferri- and ferrocytochrome c molecules has been observed by nuclear magnetic resonance. Irradiation of a partially reduced protein solution at resonance frequencies arising from protons of the oxidized state results in a decrease in the absorption due to the corresponding protons of the reduced state. The experiment quantitates the hyperfine shifts observed in this system and can be used to identify hitherto unassignable resonances. Analysis of the shifts suggests that an aromatic side chain ring lies near the edge of the heme ring.     

Multiple Morphologies of "Crew-Cut" Aggregates of Polystyrene-b-poly(acrylic acid) Block Copolymers

The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same family of highly asymmetric polystyrene-poly-(acrylic acid) block copolymers prepared in a low molecular weight solvent system. Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aqueous solution, whereas the fifth consists of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aqueous solution that have hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addition, a needle-like solid, which is highly birefringent, is obtained on drying of aqueous solutions of the spherical micelles. This range of morphologies is believed to be unprecedented for a block copolymer system.