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Cryo-electron microscopy of vitrified specimens: An approach to the study of bulk specimens

We are using and developing cryo-electron microscopy of vitrified specimens. Our main interests concern the structure of muscle and muscular components. Micrographs which generally contain periodic features are analyzed by numerical image processing methods. To detect artifacts induced by the electron microscopy techniques, we correlate our results to those obtained by X-ray diffraction. In this paper, we describe our approach to the study of bulk specimens. Vitrification of such specimens is assessed by cryo-X-ray diffraction. Microscopy is done on cryo-substituted specimens.     

Rumen degradability In sacco of physically and chemically treated oat and barley grain

The effects on rumen degradation of chemical and physical treatment of oats and barley were investigated by use of the in-sacco technique. Whole oats (75% DM) were treated with 0, 30 and 50 g NaOH, 30 g NH₃ or urea per kg DM. Three different strengths of NaOH (11, 22.5 and 45% w/v) were tested at the 30 g kg^?1 DM level. Oat hulls and crushed, shelled-crushed and shelled-whole oats were also tested, with or without addition of NaOH. Whole barley was subjected to a pearling treatment, removing 7, 11 and 18% of the DM, mainly hulls. A part of the pearled barley was also steeped in cold water for 8 h. All pearled samples were reconstituted before in-sacco incubations. Barley was also ‘clipped’ into pieces or crushed manually, using a hammer. All samples were incubated for variable amounts of time up to 24 h (48 h for oat hulls). Oat samples were analysed for DM, NDF, ADF and lignin and barley samples for DM, NDF and starch. To compare the effects on rumen pH and ammonia-N, two rumen fistulated cows were fed 50% hay and either 50% whole NaOH-treated oats (30 g NaOH kg^?1 DM) or crushed oats. In-sacco results showed that whole oats treated with 3 or 5% NaOH had 24 h DM degradation of 61% and 68%, respectively, compared with 7% for the untreated oats. Extra water additions with the NaOH had no significant effect. Shelled oats were degraded more (85%) at 24 h than whole oats treated with NaOH (max 68%). NH₃ (30%) or urea (22%). Alkali treatment had no additional effect on the shelled oats. Crushing gave the most rapid degradation for both whole and shelled oats. However, treatment with NaOH after crushing reduced degradation. Only 10% DM of the hulls were degraded at 48 h, but treatment with 5% NaOH increased this value to 55%. In the rumen study, mean rumen pH was similar for both diets, but pH variation was smaller and ammonia level consistently higher after feeding NaOH-treated oats. Increasing the pearling intensity of the barley improved starch disappearance at 24 h from 45% to 83%. Steeping further enhanced disappearance by an average of 10 percentage units. Clipping gave a degradation very similar to the highest pearling intensity.     

Electron cryomicroscopy of frozen-hydrated biological specimens: analysis of freezing artifacts by X-ray cryocrystallography.

Freezing artifacts have been evaluated by X-ray cryocrystallography on pellets of two-dimensional membrane protein crystals: purple membrane and maltoporin. The comparison of the X-ray patterns recorded when the specimens are maintained at room temperature to those obtained when the specimens are maintained at about -160 degrees C shows that (i) membrane proteins have a positive thermal dilatation coefficient: the protein crystal lattice shrinks upon cooling; (ii) the asymmetric unit of crystal containing water is changed upon freezing; the relative intensities of the diffraction rings of such crystals are different after freezing. From these results, it can be postulated that freezing may lead to partial dehydration of biological objects. Electron cryomicroscopy visualizes objects which are structurally influenced by the cooling procedure. However, our microscopy study on maltoporin crystals shows that freezing artifacts are negligible in comparison to artifacts associated with conventional techniques such as negative staining.     

Addition of alcoholes to asymmetric epoxides

Summary Formation of some asymmetric glycoles by the addition of some alcoholes or glycoles to the asymmetric epoxides in the presence of HC10₄ were investigated by ¹³C NMR and the results were simply discussed. It was cleared that the formation of the adducts were led by the electronegativity of the side groups as well as steric nature of the nucleophile involved in the reaction is mostly due to the behavior of the oxonium ions formed as intermediates in the reactions.     

Electron microscopy of frozen biological objects: a study using cryosectioning and cryosubstitution

Freezing of bulk biological objects was investigated by X-ray cryodiffraction. Freezing at atmospheric pressure of most microscopic biological samples gives rise to large hexagonal crystals and leads to poor structural preservation of these specimens. High-pressure freezing induces the formation of different ices (hexagonal, cubic and a high-pressure form) consisting of crystals having sizes smaller than those formed at atmospheric pressure. With both freezing methods, a cryoprotectant has to be added to the biological object to avoid the formation of ice crystals. However, special cases can be encountered: some biological objects contain large amounts of natural cryoprotectant or have a low water content. In these cases, vitrification can be achieved, especially using high-pressure freezing. Cryo-sectioning can be performed on vitrified samples, and the sections studied by electron cryomicroscopy. Images and electron diffraction patterns having a resolution better than 2 and 0.2 nm, respectively, can be obtained with such sections. Because samples containing crystalline ices cannot be cryosectioned, their structure has to be studied using cryosubstitution and resin embedding. We show that bacteria, yeast, and ciliate and marine worm elytrum have cellular compartments with an organization that has not been described by classical techniques relying on chemical fixation of the tissues. A high-pressure artefact affecting the Paramecium trichocysts is described. Such artefacts are not general; for example, we show that 70% of high-pressure frozen yeast cells survive successive high-pressure freezing and thawing steps.     

World oil prices,precious metal prices and macroeconomy in Turkey

We examine the long- and short-run transmissions of information between the world oil price, Turkish interest rate, Turkish lira–US dollar exchange rate, and domestic spot gold and silver price. We find that the world oil price has no predictive power of the precious metal prices, the interest rate or the exchange rate market in Turkey. The results also show that the Turkish spot precious metals, exchange rate and bond markets do not also provide information that would help improve the forecasts of world oil prices in the long run. The findings suggest that domestic gold is also considered a safe haven in Turkey during devaluation of the Turkish lira, as it is globally. It is interesting to note that there does not seem to be any significant influence of developments in the world oil markets on Turkish markets in the short run either. However, transitory positive initial impacts of innovations in oil prices on gold and silver markets are observed. The short-run price transmissions between the world oil market and the Turkish precious metal markets have implications for policy makers in emerging markets and both local and global investors in the precious metals market and the oil market.