Structure and function of mammalian DNA methyltransferases

DNA methylation plays an important role in epigenetic signalling, having an impact on gene regulation, chromatin structure, development and disease. Here, we review the structures and functions of the mammalian DNA methyltransferases Dnmt1, Dnmt3a and Dnmt3b, including their domain structures, catalytic mechanisms, localisation, regulation, post-translational modifications and interaction with chromatin and other proteins, summarising data obtained in genetic, cell biology and enzymatic studies. We focus on the question of how the molecular and enzymatic properties of these enzymes are connected to the dynamics of DNA methylation patterns and to the roles the enzymes play in the processes of de novo and maintenance DNA methylation. Recent enzymatic and genome-wide methylome data have led to a new model of genomic DNA methylation patterns based on the preservation of average levels of DNA methylation in certain regions, rather than the methylation states of individual CG sites.     

The effect of phosphate source on the sintering of carbonate substituted hydroxyapatite

Carbonate hydroxyapatite (CHAp) was synthesized by a wet precipitation method. In the synthesis, calcium oxide, H₃PO₄ and (NH₄)₂HPO₄ were applied as reactants. NH₄HCO₃ in the amount of 0.05–0.20 mol per 0.3 mol of H₃PO₄ or (NH₄)₂HPO₄ was used as the source of CO₃^2? groups. Sintering was carried out using powders and uniaxially pressed samples of carbonate and non-carbonate hydroxyapatites. The influence of synthesis conditions as well as sintering atmosphere on sinterability and phase composition of the final ceramic materials was evaluated. It was found that using properly synthesized CHAp powders and CO₂ atmosphere during heat-treatment it was possible to obtain dense CHAp ceramics with 1% of CaCO₃ as the secondary phase at the temperature 300–350 °C lower than that required for non-carbonate hydroxyapatite. Chemical stability and bioactive potential of CHAp–CaCO₃ ceramics were confirmed by in vitro tests.     

Evaluation of the amino acid content and the quality of protein in florets of white cauliflower: raw, cooked, and prepared for consumption after freezing

The aim of the work was to evaluate the retention of amino acids in white cauliflower florets and the quality of protein. The investigation concerned the raw material and florets prepared for consumption, both from the fresh material and from two types of frozen product: one obtained using the traditional method (blanching–freezing–refrigerated storage–cooking); and the other using a modified method (cooking–freezing–refrigerated storage–microwave defrosting and heating). In 100 g of the raw material the total amino acid content was 1674 mg; the content was significantly higher only in the modified frozen product. The amino acid content found in 16 g N did not significantly differ between the investigated samples, varying in the range of 79.76–87.53 g. Essential amino acids constituted 43–45%. In all the samples the limiting amino acids were cystine with methionine, with glutamic and aspartic acids dominating.     

Manufacturing of highly porous calcium phosphate bioceramics via gel-casting using agarose

There is a technological need for highly porous bioceramics to be produced in an environmentally friendly manner. Gel-casting of highly porous HAp-(α-TCP) (CaP) foams using agarose as a gelling agent was investigated. Foaming of gel-cast suspension was performed at the temperature of 60 °C followed by transformation of the foams from a liquid state to a gelled state by cooling them to 15 °C. The sintered (1250 °C, 2 h soaking time) foams were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption isoterm and Hg porosimetry. XRD study revealed that additives used in the gel-casting process did not influence the phase composition of the investigated materials. The macroporous microstructure of HAp-(α-TCP) foams was typically composed of approximately spherical pores (cells) interconnected by circular windows. The foams exhibited a broad pore size distribution with cells and windows ranging from 250 to 900 μm, and from 25 to 250 μm, respectively. The mode for spherical pore size was approximately 500 μm while the above value for window was ∼100 μm. Additionally, the small amount of wall microporosity in the range of 0.2–0.9 μm was confirmed by SEM and Hg porosimetry. The obtained porous (P = 90%) HAp-(α-TCP) scaffolds with interesting two types of macropores and a small amount of micropores seem to be a promising bone substitution material.     

Peritektoidische Reaktion in einem Stahl mit rd. 1% C und 18% Cr

Betrachtungen zur peritektoidischen Reaktion γ + M₂₃C₆ → M₇C₃ in einem Stahl mit rd. 1% C und 18% Cr im Zusammenhang mit früheren Schrifttumsangaben. Elektrolytische Isolation der Phasen nach unterschiedlichen Austenitisierungsbedingungen des Stahles und chemische sowie Röntgenanalysen der gebildeten Phasen sowie vergleichende metallographische Beurteilung der entstandenen Gefüge. Erörterung der Versuchsergebnisse im Hinblick auf Ablauf, Morphologie und Bildungsmechanismus der peritektoidischen Reaktion unter Berücksichtigung der Diffusionsvorgänge und vorangehender Schrifttumsangaben.     

Sorption mechanism of copper in chitosan hydrogel

Sorption mechanism of copper for spherical hydrogel structures formed by the phase inversion method are determined. Based on equilibrium and the research of structural attempt was made to explain the mechanism of sorption. Equilibria was describe by Langmuir, Langmuir–Freundlich equation. The chemical character of sorption was confirmed by IR and WAXS and XPS spectra.     

Carbide equilibria in austenitic Cr–Ni steel at 1273 K

The phase structure and local composition was studied in a 24% Cr/19% Ni steel after annealing at 1273 K in different carburizing atmospheres. A peritectoid transformation of M₂₃C₆ into M₇C₃ was detectable, if the carbon activity exceeded a value near a^R_C = 0.015 depending on the chromium impoverishment and nickel enrichment in the austenite surrounding the M₂₃C₆ carbides. On the basis of parameters given by Hillert, Hertzman et al. the phase equilibria between austenite, M₂₃C₆ and M₇C₃ were calculated and compared to the experimental results. Correspondence between measured and calculated equilibrium compositions was reached, if a solution parameter L_Cr–Ni = ? 26 000 J/mole was chosen.     

Natural Micas Intercalated with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Modified with Transition Metals as Catalysts of the Selective Oxidation of Ammonia to Nitrogen

Natural cationic layered clays—vermiculite and phlogopite—pretreated with acids were intercalated with alumina pillars. In next step, transition metals were deposited on the surface of pillared interlayer clays (PILC) by a liquid ion exchange method. The catalyst samples were characterized with respect to: composition (EPMA), structure (XRD), texture (BET), surface acidity (NH₃-TPD) and coordination of deposited transition metals (UV–vis-DRS). The modified clays were tested in the role of catalyst for the selective oxidation of ammonia to nitrogen. In a series of the studied samples the best catalytic performance presented alumina pillared vermiculite modified with copper.     

Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

The microscopic densification mechanisms of metallic systems (TiAl, Ag-Zn) by spark plasma sintering (SPS) have been studied by simulations and experiments. Finite element simulations showed that, despite very high current densities at the necks between metallic powder particles (≈5 × 10⁴ A/cm²), only very limited Joule overheating can be expected at these locations (<1°C), because of very fast heat diffusion. The microscopic plasticity mechanisms under these high electric currents have been studied by transmission electron microscopy. For this purpose, thin foils have been extracted by focused ion beam at the necks between TiAl powder particles. This is the first time, to the best of our knowledge, that microscopic plasticity mechanisms at the necks between powder particles are investigated by TEM during densification of a metallic powder. Dislocation glide and climb mechanisms were identified, followed by recovery and recrystallization. The elementary mechanism kinetically controlling these phenomena is proposed to be bulk diffusion of Al, which activation energy (360 kJ/mol) is close to the activation energy measured for densification (308 ± 20 kJ/mol). Comparisons of densification kinetics by SPS (≈60-110 A/cm²) and by hot pressing (0 A/cm²) showed no influence of current on these mechanisms. Finally, reaction experiments in the Ag-Zn system did not show any influence of very high currents (>1000 A/cm²) on diffusion kinetics. Consequently, densification by SPS occurs by classical mechanisms not affected by the current.