New shapes and sizes: a T-tube coronary conduit

A novel type of coronary artery graft named a T-tube conduit is described. This reversed saphenous graft, coming in three different variations, is useful at long arteriotomies, at revision redo anastomoses, and when size mismatch exists between vein and artery.     

MR angiography of aneurysm models of various shapes and neck sizes

PURPOSE: To investigate the signal intensity of lateral and terminal saccular aneurysm models with differing neck sizes using three-dimensional time-of-flight (TOF) MR angiography with various imaging parameters. METHODS: The study included four lateral and four terminal saccular aneurysm models with pulsatile flow. The height and fundus diameter were 10 mm; the neck diameters were 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively. Each aneurysm model was examined with fast imaging with steady-state precession MR sequences with parameters of 20-140/7 (repetition time/echo time) and flip angles of 10 degrees to 30 degrees. Signal intensity was measured and compared among the models. RESULTS: Three-dimensional TOF MR angiography with the shorter repetition time and/or larger flip angle showed weaker signal intensity in the aneurysm models. Stronger signal intensity was obtained in the terminal saccular aneurysm models and/or the models with a wider neck than in the lateral saccular aneurysm models and/or the models with a narrower neck. In some aneurysm models, longer repetition times produced greater signal intensity than that of background brain models, but not in aneurysms with narrow necks. CONCLUSION: Noncontrast 3-D TOF MR angiography delineated terminal saccular aneurysms and/or aneurysms with wider necks and did not delineate lateral saccular aneurysms and/or aneurysms with narrower necks. Longer repetition times are recommended to allow the spins flowing into the aneurysms to recover.     

How to analyze electron micrographs of rafts of actin filaments crosslinked by actin-binding proteins

Actin bundles are common cytoskeletal structures but ones which are usually polymorphic, varying from bundle to bundle. Two-dimensional arrays of actin filaments crosslinked by actin-bundling proteins are more tractable structures to analyze than are the three-dimensional bundles found in cells. The first step in analyzing these two-dimensional "rafts" is to determine the spatial relationships between neighboring filaments. It is difficult to discern such relationships by inspection of the electron micrographs of rafts, but easy by examination of the Fourier transforms. We provide theory and examples of the analysis of transforms of rafts, and show that different bundling proteins give rise to different kinds of rafts.     

Characterisation of niobium and vanadium hydrides by electron energy loss spectroscopy and by STEM

The transmission electron energy loss spectra from hydrogen-containing vanadium and niobium are compared with those from the pure metals. The hydrogen induces an additional small energy loss peak at very low energies, well below that due to the plasmon loss. This peak can be interpreted as due to a band of states induced by the hydrogen several eV below the conduction bands of the metal. Because these experiments are performed in a STEM, it is possible to verify the structure of the hydride by electron microscopy and diffraction and to be certain that the energy-loss spectra come from well characterised material.     

Characterisation of urea-denatured states of an immunoglobulin superfamily domain by heteronuclear NMR

The structural and dynamic properties of an immunoglobulin superfamily domain (IgSF), Ig 18', have been characterised by NMR at 285 K, in the presence of 4.2 M and 6.0 M urea, respectively. Analysis of chemical shift deviations, 3JHNHalpha coupling constants, sequential NOE pattern, and 15N relaxation data reveals that although the two urea-denatured states are highly disordered, some local turn-like residual structures do exist. Moreover, some distinct differences between the properties of the two denatured states are observed. In 4.2 M urea-denatured Ig 18', regions 80-83 and 86-92 adopt turn-like conformations, furthermore, region 84-93 is involved in slow exchange processes that occur on a micro- to millisecond time-scale. In the 6.0 M urea-denatured state, these turn-like conformations are less occupied, and chemical exchange processes in region 84-93 are largely reduced. In contrast, region 32-36 has persistent turn-like structures in both urea-denatured states. Some correlation between the spectral density function at 0 frequency, Jeff(0), for the urea-denatured states and the secondary structure elements of the folded state have been observed. Except for the terminal regions, residues corresponding to beta-strands have higher Jeff(0) values compared to residues corresponding to loops. The characterisation and comparison of the two urea-denatured states highlight residues that possess properties that may be crucial for the initiation of folding of this domain.     

1H NMR spectroscopy studies of Huntington's disease: correlations with CAG repeat numbers

Huntington's disease (HD) is the result of an expanded (CAG) repeat in a gene on chromosome 4. A consequence of the gene defect may be progressive impairment of energy metabolism. We previously showed increased occipital cortex lactate in HD using localized 1H spectroscopy. We have now extended these studies to show an almost threefold elevation in occipital cortex lactate in 31 HD patients as compared with 17 normal control subjects (p < 10(-11)). The spectra in three presymptomatic gene-positive patients were identical to normal control subjects in cortical regions, but three in eight showed elevated lactate in the striatum. Similar to recently reported increases in task-related activation of the striatum in the dominant hemisphere, we found that striatal lactate levels in HD patients were markedly asymmetric (higher on the left side). Markers of neuronal degeneration, decreased N-acetylaspartate (NAA)/creatine and increased choline/creatine levels, were symmetric. Both decreased NAA and increased lactate in the striatum significantly correlated with duration of symptoms. When divided by his or her age, an individual's striatal NAA loss and lactate increase were found to directly correlate with the subject's CAG repeat number, with correlation coefficients of 0.8 and 0.7, respectively. Similar correlations were noted between postmortem cell loss and age versus CAG repeat length. Together, these data provide further evidence for an interaction between neuronal activation and a defect in energy metabolism in HD that may extend to presymptomatic subjects.     

Characterisation of rare earth minerals with field emission scanning electron microscopy

Abstract

Rare earth elements are becoming increasingly in demand, due to their prevalence in both renewable energy devices and high end electronics. The characterisation of the composition and morphology of the various phases that have valuable rare earth elements in the ores are needed in conjunction with the study of their physicochemical properties to optimise industrial process to extract the minerals containing the rare earth elements. Rare earth bearing minerals contain many elements with overlapping X-ray peaks (L- and M-lines) with an energy dispersive spectrometry detector, requiring a high degree of X-ray energy resolution. A program was developed to obtain the intensity of each peak by deconvolution of the X-ray spectrum. Low accelerating voltage of less than 5 kV and small beam diameter of less than 10 nm of a cold field emission scanning electron microscope allow x-ray microanalysis on the nanometre scale. A 100 nm wide phase was observed at 4 kV on a backscattered electron micrograph. Furthermore, a small beam diameter of less than 10 nm was used for identification of small phases of a few micrometres.

Les éléments de terre rare sont de plus en plus en demande, grâce à leur prévalence tant dans les dispositifs d’énergie renouvelable que dans l’électronique de haute gamme. On a besoin de caractériser la composition et la morphologie des différentes phases qui contiennent des terres rares de valeur dans les minerais, en combinaison avec l’étude de leurs propriétés physico-chimiques, afin d’optimiser le procédé industriel d’extraction des minéraux contenant les terres rares. Les minéraux porteurs de terre rare contiennent plusieurs éléments ayant des pics de rayons x qui se chevauchent (lignes L et M) avec un détecteur de spectroscopie à dispersion d’énergie, nécessitant une haute résolution énergétique. On a développé un programme visant à obtenir l’intensité de chaque pic par déconvolution du spectre de rayons x. Un faible voltage d’accélération de moins que 5 kV et un faisceau à faible diamètre de moins que 10 nm d’un microscope électronique à balayage par cathode froide permettent la microanalyse des rayons x à l’échelle du nanomètre. On a observé une phase de 100 nm de largeur à 4 kV sur une micrographe d’électrons rétrodiffusés. De plus, on a utilisé un faisceau de faible diamètre de moins que 10 nm pour l’identification de petites phases de quelques μm.     

Nuclear pore complex number and distribution throughout the Saccharomyces cerevisiae cell cycle by three-dimensional reconstruction from electron micrographs of nuclear envelopes

The number of nuclear pore complexes (NPCs) in individual nuclei of the yeast Saccharomyces cerevisiae was determined by computer-aided reconstruction of entire nuclei from electron micrographs of serially sectioned cells. Nuclei of 32 haploid cells at various points in the cell cycle were modeled and found to contain between 65 and 182 NPCs. Morphological markers, such as cell shape and nuclear shape, were used to determine the cell cycle stage of the cell being examined. NPC number was correlated with cell cycle stage to reveal that the number of NPCs increases steadily, beginning in G1-phase, suggesting that NPC assembly occurs continuously throughout the cell cycle. However, accumulation of nuclear envelope observed during the cell cycle, indicated by nuclear surface area, is not continuous at the same rate, such that the density of NPCs per unit area of nuclear envelope peaks in apparent S-phase cells. Analysis of the nuclear envelope reconstructions also revealed no preferred NPC-to-NPC distance. However, NPCs were found in large clusters over regions of the nuclear envelope. Interestingly, clusters of NPCs were most pronounced in early mitotic nuclei and were found to be associated with the spindle pole bodies, but the functional significance of this association is unknown.     

Signal to noise enhancement in dark field electron micrographs of vasopressin: filtering of arrays of images in reciprocal space

A technique for filtering arrays of images of dispersed molecules is presented which takes advantage of the crystallographic properties of regular arrays and the rapidity of optical treatment. A filter in reciprocal space consisting of perforations in a square or rectangular lattice, as determined by the image arrrangement, reduces noise and averages the images simultaneously by transmitting only regularly recurring image structure. The filter is universal for all image contents and introduces no additional biases. The signal to noise improvement approaches square root N for N independent images of the same molecule in the same configuration. The procedure which is simple, rapid and inexpensive, is demonstrated with the aid of dark field electron micrographs of the protein vasopressin and combined with iodination of that molecule to elucidate its structure.     

Graphical and statistical comparison of various size distribution measurement systems using metal powders of a range of sizes and shapes

Abstract

The purpose of this paper was to describe the results of particle size analysis from image analysis, sieving analysis and dry or wet dispersion laser diffraction and compare these techniques. Measurements were made on particle systems of different morphological characteristics, size and particle size distribution widths using the most common metal powders. The results show reasonably good agreement between the different techniques concerning the shape of the distribution. However, there is a discrepancy regarding the absolute values, which can be explained by the fact that the techniques used are based on different measuring principles. The study suggests that image analysis is a powerful tool in characterising non-spherical particles, especially elongated particles and that caution needs to be taken when evaluating the sizing results of non-spherical particles using laser diffraction.     

Characterisation of the major intrinsic protein (MIP) from bovine lens fibre membranes by electron microscopy and hydrodynamics

The major intrinsic protein (MIP) from bovine lens fibre membranes has been purified from unstripped membranes using a single ion-exchange chromatography step (MonoS) in the non-ionic detergent octyl-beta-D-glucopyranoside (OG). SDS-PAGE has confirmed the purity of the preparation and thin-layer chromatographic analysis has shown that the protein is virtually lipid-free. To establish a stable and monodisperse protein sample, we exchanged OG with decyl-beta-D-maltopyranoside (DeM), another non-ionic detergent, by gel-filtration column chromatography. We conclude that the resulting protein/detergent complex is composed of four copies of MIP (a tetramer) and a detergent micelle. This conclusion is based on: (1) measurement of the weight-average molecular mass (Mw,app) of the protein moiety in the protein/detergent complex by sedimentation equilibrium; (2) measurement of the apparent molecular mass of the complexes formed by MIP in OG, in DeM, in dodecyl-beta-D-maltopyranoside (DoM) and in sodium dodecylsulphate (SDS) by gel filtration; (3) measurement of the apparent molecular mass of pure detergent micelles; (4) measurement of the predicted change in the molecular mass of the MIP/DeM complex after partial enzymatic proteolysis; and (5) measurement of the size and shape of the MIP/detergent complex by electron microscopy and single-particle analysis. Therefore, the tetragonal arrangement of MIP observed in both plasma membranes and junctional membranes in lens fibre cells is maintained in solution with non-ionic detergents.     

Nonpolar environment of tryptophans in erythrocyte water channel CHIP28 determined by fluorescence quenching

CHIP28 is an abundant water-transporting protein in erythrocytes, kidney proximal tubule, and other fluid-transporting tissues. To determine the environment of the four tryptophans in CHIP28, fluorescence spectra and quenching by polar and nonpolar compounds were measured in stripped human erythrocyte membranes containing CHIP28 and in proteoliposomes reconstituted with purified CHIP28; comparative studies were performed in membranes containing MIP26. Functional analysis showed that CHIP28 water permeability was not affected by the polar quenchers iodide and acrylamide nor the nonpolar n-anthroyloxy fatty acids (n-AF). The emission maximum of CHIP28 tryptophan fluorescence was at 324 +/- 2 nm and did not change with the addition of quenchers; the maximum for MIP26 was at 335 +/- 5 nm. There was weak quenching of CHIP28 tryptophan fluorescence by the polar compounds iodide and acrylamide, with Stern-Volmer constants of 0.13 and 0.71 M-1, respectively. HgCl2 inhibited water permeability by > 95% at 50 microM and quenched CHIP28 fluorescence reversibly by up to 70% with a biphasic concentration dependence; quenching by HgCl2 and acrylamide was not additive. The membrane-associated n-AF probes quenched CHIP28 fluorescence by up to 80% with the greatest quenching for n = 2 and 12; addition of HgCl2 or acrylamide after n-AF caused a small, anthroyloxy-position-dependent increase in quenching which was greatest at n = 6. These studies indicate that the tryptophans in CHIP28 are in a nonpolar, membrane-associated environment. Mathematical modeling of the n-AF results suggests that the tryptophans are clustered near the surface and center of the bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)