High-voltage high-resolution electron microscopy study of alkaline-earth copper oxides

Two families of alkaline-earth copper oxides are studied by using high-voltage high-resolution electron microscopy. One is Sr(n-1) Cu(n)O(2n-1) (n = 2, 3), the so-called spin-ladder compounds, and the other is ACuO2 (A = Ca-Sr) crystallizing in the infinite-layer structure, which is a parent structure for all copper oxide superconductors. It is demonstrated in the former compounds that oxygen columns as well as metal columns are directly imaged in a "structure" image. Moreover, twin-related lattice defects, which can be the origin of free Cu2+ spins observed previously in magnetic measurements, have been detected in SrCu2O3. An interesting irradiation effect under a 1,000-kV electron beam has been observed in the infinite-layer compound: An unusual structural phase transformation to a NaCl-type lattice is induced, accompanied by the formation of nm-size twin domains.     

Image processing based on the combination of high-resolution electron microscopy and electron diffraction

A method of crystal structure determination by electron crystallographic image processing based on the combination of high-resolution electron microscopy (HREM) and electron diffraction is introduced. It consists of two stages: image deconvolution and resolution enhancement. In the first stage an image taken at an arbitrary defocus condition is transformed into the structure image with the resolution depending on the resolution of the electron microscope. In the second stage the image resolution is enhanced to the diffraction resolution limit by combining the electron diffraction data and using the phase extension technique so that in the final image most unoverlapped atoms can be resolved individually. The experimental diffraction intensities are corrected for approximating to square structure factors. The principle of the image processing and the procedure of diffraction intensity correction are briefly described and the results of applications are illustrated. Since the method is based on the weak phase object approximation (WPOA), the validity of WPOA is discussed by introducing an approximate image contrast theory named pseudo weak phase object approximation (PWPOA) to demonstrate the image contrast change with the crystal thickness for very thin crystals.     

Rho-associated kinase of chicken gizzard smooth muscle

Rho-associated kinase (Rho-kinase) from chicken gizzard smooth muscle was purified to apparent homogeneity (160 kDa on SDS-polyacrylamide gel electrophoresis) and identified as the ROKalpha isoform. Several substrates were phosphorylated. Rates with myosin phosphatase target subunit 1 (MYPT1), myosin, and the 20-kDa myosin light chain were higher than other substrates. Thiophosphorylation of MYPT1 inhibited myosin phosphatase activity. Phosphorylation of myosin at serine 19 increased actin-activated Mg+-ATPase activity, i.e. similar to myosin light chain kinase. Myosin phosphorylation was increased at higher ionic strengths, possibly by formation of 6 S myosin. Phosphorylation of the isolated light chain and myosin phosphatase was decreased by increasing ionic strength. Rho-kinase was stimulated 1.5-2-fold by guanosine 5'-O-3-(thio)triphosphate.RhoA, whereas limited tryptic hydrolysis caused a 5-6-fold activation, independent of RhoA. Several kinase inhibitors were screened and most effective were Y-27632, staurosporine, and H-89. Several lipids caused slight activation of Rho-kinase, but arachidonic acid (30-50 microM) induced a 5-6-fold activation, independent of RhoA. These results suggest that Rho-kinase of smooth muscle may be involved in the contractile process via phosphorylation of MYPT1 and myosin. Activation by arachidonic acid presents a possible regulatory mechanism for Rho-kinase.     

Different genotypes causing indiscernible patterns of A expression on A(el) red blood cells as visualized by scanning immunogold electron microscopy

OBJECTIVE: Cerebrospinal fluid (CSF) diagnoses encompass a wide spectrum of conditions. The authors review one institution's CSF cytology results over an 11-year period. DESIGN AND SETTING: A retrospective study of 5951 CSF specimens generated between 1985 and 1995. Specimens from pediatric patients (<19 years of age) from the same time period were separately identified. RESULTS: A total of 5561 adult and 390 pediatric CSF specimens were interpreted. A diagnosis of "negative for malignant cells" was assigned in 5171 (93%) of the adult cases and in 351 (90%) of the pediatric cases. Specific infectious organisms were identified in 26 adult specimens and one pediatric specimen. Cryptococcus was the most common infectious agent observed (n = 23 adults), and Toxoplasma was the sole pediatric infectious agent. Two hundred seventy-six (5%) adult cases and 31 (8%) pediatric cases were positive for malignant cells. Diagnoses included metastatic tumors (adult, 140 [51%]; pediatric, 0); lymphoma/leukemia (adult, 112 [41%]; pediatric, 4 [13%]); malignant unclassified neoplasms (adult, 9 [3%]; pediatric, 0); and primary central nervous system neoplasms (adult, 12 [4%]; pediatric, 27 [87%]). Medulloblastoma was the most common pediatric neoplasm (n = 21). There were 105 (2%) adult cases and 8 (2%) pediatric cases with atypical cells present. Atypical lymphoid cells were the most common type in adult cases (53%). CONCLUSIONS: In our experience, infectious agents were rarely identified in pediatric CSF specimens. In adult specimens, the most commonly identified organisms was Cryptococcus. Primary central nervous system neoplasms accounted for a higher percentage of CSF specimens in the pediatric population than in the adult population. The most commonly identified malignancy in adults was metastatic neoplasms, and in children, medulloblastoma.     

Tubules of the trans Golgi apparatus visualized by immunoelectron microscopy

Tubules constitute an integral part of the Golgi apparatus and have been shown to form a complex and dynamic network at its trans side. We have studied in detail structural features of the trans Golgi network and its relationship with the cisternal stack in thin sections of Lowicryl K4M embedded human absorptive enterocytes by immunolectron microscopy. Immunoreactive sites for alpha1,3 N-acetylgalactosaminyltransferase and blood group A substance were detectable throughout the cisternal stack and the entire trans Golgi network. Furthermore, the entire trans Golgi network was reactive for CMPase activity. Evidence for two kinds of tubules at the trans side of the Golgi apparatus was found: tubules that laterally connect adjacent and distant cisternal stacks, and others extending from central and lateral portions of trans cisternae to form the complex and extensive trans Golgi network. Trans cisternae showed often the peeling-off phenomenon and were continuous with the trans Golgi network. Both, trans cisternae and tubules of the trans Golgi network exhibited regionally buds and vesicles with a lace-like, non clathrin coat, previously reported by others in NRK cells, which contained glycoproteins with terminal N-acetylgalactosamine residues. These buds and vesicle are therefore involved in constitutive exocytosis.     

The sporulation process in Thermomonospora fusca as revealed by scanning and transmission electron microscopy

The sporulation process in the thermophilic actinomycete Thermomonospora fusca was observed by scanning and transmission electron microscopy. As shown by scanning electron microscopy, spores were produced primarily on aerial hyphae and first appeared as bud-like enlargements at the tips of short multibranched sporophores. Young spores were oval to spherical in shape with a smooth surface. As they matured spores enlarged and developed a rough and globular covering, which was quite fragile and easily detached from the spore. This outer layer, as observed by transmission electron microscopy, was thought equivalent to the sheath of other Thermomonospora species. In cross section, mature spores exhibited a thick spore coat underneath the outer globular layer. This spore coat was usually observed as a single layer, but some spores produced a bilayered coat. No multilayered spore coat or spore cortex was observed in the heat-sensitive spores of T. fusca. They were, therefore, shown to be aleuriospores (microcondia), and not endospores.     

The classification of short range order by electron microscopy

After discussion of the various modelling concepts, a broad classification of short range order (sro) is suggested, differentiating between uniform and bounded ‘micro-domains’ and unbounded ‘static concentration wave packets’. It is explained why this classification is physically useful, and how transmission electron microscopy (TEM) imaging provides a direct means of differentiating between these two models. The analogy between this model classification and the microcrystallite-amorphous problem in the classification of ‘glassy’ structures is discussed.Criticisms [1] of our earlier work [2] on electron diffraction information obtained for Ni₄Mo have been carefully analysed. We could find no reason to change our view of the nature of s.r.o. in this particular material. Our essential conclusion is that it is unrealistic to describe sro in quenched Ni₄Mo as of microdomain type.     

The growth of antiphase domains in Cu3Au as studied by transmission electron microscopy

The changes in the antiphase domain structure of stoichiometric Cu₃Au during ordering after quenching from aboveT _c have been studied by means of transmission electron microscopy. The growth of the domains was found to satisfy aD ² ∞ t relation in agreement with previous X-ray diffraction measurements. The activation energy determined for the process (42 kcal per mole) is also in agreement with the previous work. An increase in quenching temperature gave no effect on the domain size achieved by a particular ordering treatment. Measurements of the domain size distribution at various stages during growth indicate that the domain structure is not completely irregular. Certain domain sizes which are multiples of a unit domain size are preferred. During the early stages of domain growth the behavior appears to be consistent with a diffusion model of the ordering process similar to that applied to spinodal decomposition.     

Real-Time atomic-level observations of in situ chemical reactions and transformations utilizing high-resolution electron microscopy

Three studies ofin situ chemical reactions or transformations utilizing real-time video recording of high-resolution microscopic images to reveal atomic resolution details are reported. In one study, the removal of a twin plane separating a surface promontory consisting of several hundreds of atoms from the main body of a TbO_x crystal is observed. In another study of a leached TbO_x specimen, the decomposition of a Tb(OH)₃ surface impurity is followed as the oxide product is accreted to the main body of the TbO₂ crystal. In a third example, a crystal of modified PbO2 grown from acid solution displays, in high resolution, rapid cooperative movement of scores to hundreds of atoms over the crystal surface before finally decomposing, presumably with loss of hydrogen, toβ-PbO₂. This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

Structural organization of the intact bacterial cellulosome as revealed by electron microscopy

The architecture of the intact cellulosome of Clostridium thermocellum, a huge extracellular multi-polypetide bacterial enzyme complex engaged in degradation of cellulose, was investigated by electron microscopy. This was done because former electron microscopic studies aimed at elucidation of the structure of polycellulosomes and cellulosomes were restricted by the fact that data on macromolecular details could only be derived from deformed or disrupted enzyme complexes, or by application of cryo preparation and imaging techniques yielding insufficient resolution. The shape of well-preserved cellulosomes was more or less spherical, often similar to that of an olive fruit with a cavity. Therein, multiple fibrillar structures could be visualized, interpreted to be the proximal stretches of copies of the fibrillar protein Cip A ('scaffoldin'), the nonenzymatic scaffolding protein known to function as attachment site for the enzymatic subunits, as well as fibrillar parts of anchoring proteins. The enzymatic subunits were depicted to be attached, in a repetitive fashion, to the distal stretches of the Cip A proteins. The enzymatic subunits were seen, in the intact cellulosome, to form a shell-like complex substructure surrounding the cavity. Obviously, this kind of architecture makes sure that the catalytic domains of the enzymatic subunits are exposed to the environment, and, hence, to the substrate, the cellulose fibrils. Attempts were made to demonstrate the alternating occurrence of coiled domains and fibrillar stretches along the elongated protein Cip A previously characterized by sequencing, X-ray, and NMR studies. To this end, Cip A molecules, with adhering enzymatic subunits, were partially removed from their native location within the cellulosome, "stretched" by hydromechanical forces directly on the electron microscopic support film, negatively stained, and depicted by electron microscopy. The alternating occurrence of presumed coiled domains and fibrillar stretches along Cip A could be visualized, together with detached enzymatic subunits found on the support film.     

The role of ledges in vapor/solid phase transformations observed by low-energy electron microscopy and photoemission electron microscopy

Adsorption at monatomic ledges was observedin situ, in real time, during the epitaxial growth of Cu deposited from the vapor phase onto Mo{110}. Migration of monatomic ledges of Cu was followed during both growth and sublimation near equilibrium conditions and was independent of crystallographic direction in accord with fundamental theories of crystal growth. Evidence is presented showing that the two-dimensional (2-D) vapor pressure of Cu Actatoms on the terraces near curved ledges differs from that near straight ledges. Formerly with the Technical University of Clausthal.This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

A high-resolution transmission electron microscopy study of the precipitation process in a dilute Ti-N alloy

The precipitation processes in dilute nitrogen alloys of titanium have been examined in detail by conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The alloy Ti-2 at. pct N on quenching from its high-temperatureβ phase field has been found to undergo early stages of decomposition. The supersaturated solid solution (α″-hcp) on decomposition gives rise to an intimately mixed, irresolvable product microstructure. The associated strong tweed contrast presents difficulties in understanding the characteristic features of the process. Therefore, HREM has been carried out with a view to getting a clear picture of the decomposition process. Studies on the quenched samples of the alloy suggest the formation of solute-rich zones of a few atom layers thick, randomly distributed throughout the matrix. On aging, these zones grow to a size beyond which the precipitate/matrix interfaces appear to become incoherent and theα′ (tetragonal) product phase is seen distinctly. The structural details, the crystallography of the precipitation process, and the sequence of precipitation reaction in the system are illustrated.     

Topology of the morphological domains of the chaperonin GroEL visualized by immuno-electron microscopy

Electron microscopy of the tetradecameric double-ring complex of GroEL reveals a four-layered structure, indicating that the 58 kDa subunits are composed of two major morphological domains. We have used immuno-electron microscopy to assign these domains to the corresponding segments of the GroEL sequence. Upon chemical modification of GroEL with N-ethylmaleimide, protease treatment in the presence of ATP or ADP generates GroEL fragments of 15 kDa (N15; residues 1-141) and 40 kDa (C40; residues 153-531). As visualized by scanning transmission electron microscopy, affinity-purified antibodies directed against C40 recognize the outer layers, whereas antibodies against N15 interact with the equatorial portions of the GroEL double-ring. Thus, the two major domains of the subunits in the chaperonin complex are arranged in the order C40-N15:N15-C40. The single-ring chaperonin co-factor GroES interacts with the C40 domain while the ATP-binding site of GroEL is probably close to the junction between N15 and C40.