基于酵母产孢的syntaxin家族蛋白SNARE区域功能分析

真核细胞中大部分膜融合过程由SNARE蛋白介导,但其功能和调节机制尚未完全清楚。酵母孢子形成是研究囊泡融合机制包括SNARE蛋白的理想模型系统。在该过程中涉及t-SNARE蛋白Sso1,它是突触囊泡融合所需蛋白syntaxin 1A的同源物,两者SNARE区域有51%的同源性。尽管如此,将SSO1的SNARE区域完全替换成syntaxin 1A,而构建的嵌合体却无法回补sso1△突变的产孢缺陷。为了确定哪些残基为Sso1功能所必须,作者进行了嵌合体和突变分析,发现Sso1/syntaxin 1A嵌合体中syntaxin 1A的SNARE区域的220位丙氨酸换成谷氨酸后获得产孢功能。另外,Sso1发生相应的突变-218位谷氨酸突变成丙氨酸后失去其功能。因此,218位谷氨酸残基为Sso1产孢功能所必须。     

Preparation of sharp-melting hard palm midfraction and its use as hard butter in chocolate

Preparation of hard palm midfractions (PMF) and its use as a cocoa butter equivalent ingredient were studied. Hard PMF is obtained by multistep fractionation of palm oil involving dry fractionation (DF) and/or solvent fractionation (SF), usually using hexane or acetone. From our experience, in acetone, a polar solvent, symmetrical 1,3-disaturated triacylglycerols tend to selectively crystallize more than nonsymmetrical 1,2- or 2,3-disaturated triacylglycerols, making it suitable for obtaining the solid midfraction. Unfortunately, triacylglycerols are very soluble in hexane, and temperatures at least 15 degrees lower than those required for acetone must be used for equivalent crystal yields. On the other hand, DF is a less expensive and safer process. Thus, multistep fractionation combining DF and SF using acetone was developed to achieve sufficient removal of high-melting components, and further enrichment of 1,3-dipalmitoyl-2-oleoylglycerol and the hard PMF was obtained by triple-step fractionation of palm olein or double-step fractionation of soft PMF. Compared to conventional hard PMF, this hard PMF had a steeper melting curve and better snapping and sharp-melting qualities when used in chocolate. Heat resistance of the hard PMF chocolate was similar to the conventional hard PMF chocolate, and its bloom resistance could be improved by adding polyglycerol fatty acid esters.     

Mycotoxicological quality evaluation of corn samples used by processing industries in the Northern region of Paraná State,Brazil

Based on fungal and fumonisin contamination of 870 freshly harvested samples, the quality of corn used by processing industries in the Northern region of Paraná State, Brazil (2003 and 2004 crop-year) was evaluated. Sampling was carried out for each crop at two points in the production chain, i.e. at reception by the processors and at the pre-drying step. Corn samples were more frequently contaminated with Fusarium sp. (100%) and Penicillium sp. (84.1–95.3%) than Aspergillus sp. (5.6–19.8%). Fumonisin B₁ (FB₁) was detected in all samples from the two points in both crop-years. FB₁ levels ranged 0.02–11.83 µg g^?1 in the reception and 0.02–10.98 µg g^?1 in the pre-drying samples of the 2003 crop. Samples from the 2004 crop showed FB₁ levels ranging 0.03–12.04 µg g^?1 in the reception and 0.06–7.74 µg g^?1 in the pre-drying samples. FB₂ levels ranged 0.02–5.25 µg g^?1 in the reception and 0.01–7.89 µg g^?1 in the pre-drying samples (2003 crop-year). In samples from the 2004 crop, FB₂ levels ranged 0.02–6.12 µg g^?1 in the reception and 0.05–3.47 µg g^?1 in the pre-drying samples. Low fumonisin levels were detected in most corn samples used by processors in the Northern region of Paraná State, showing a decreasing trend in fumonisin contamination over the years.     

Purification and biochemical properties of pepsins from the stomach of skipjack tuna (Katsuwonus pelamis)

Pepsins 1 and 2 from the stomach of skipjack tuna (Katsuwonus pelamis) were purified to homogeneity by using a series of chromatographic purification involving DEAE-cellulose, Sephadex G-50 and Sephadex G-75 with increase in purity of 246-fold and 213-fold, respectively. Molecular weights of pepsins 1 and 2 were estimated by SDS–PAGE to be 33.9 and 33.7 kDa, respectively. The N-terminal amino acid sequences of the first 20 amino acids of both isoenzymes were YQDGTEPMTNDADLSYYGVI. The optimal pH and temperature for pepsin 1 were 2.5 and 50 °C, respectively, while pepsin 2 showed optimal activity at pH 2.0 and 45 °C. The activity of two pepsins was stable in the pH range of 2–5 and at temperatures up to 50 °C. The activity of purified pepsins was strongly inhibited by pepstatin A in a dose-dependent manner. SDS and cysteine showed inhibitory effects toward both pepsins. Activity of pepsin 2 was slightly activated by NaCl, but NaCl had no effect on pepsin 1. Pepsins 1 and 2 had high affinity and hydrolytic activity toward hemoglobin with K _m of 54 and 71 μM, respectively. k _cat of pepsins 1 and 2 were 38.1 and 44.3 s⁻¹, respectively. Both pepsins effectively hydrolyzed bovine serum albumin, egg white, natural actomyosin from brownstripe red snapper muscle and acid-solubilized collagen from arabesque greenling skin. Nevertheless, the hydrolytic activity was slightly less than that of pepsin from porcine stomach.     

Vitamin E reduces cholesterol esterification and uptake of acetylated low density lipoprotein in macrophages

The effects of vitamin E on cholesteryl ester (CE) metabolism in 1774 cells were examined. Pretreatment of 1774 cells with vitamin E at concentrations above 50 μM significantly decreased acetylated low density lipoprotein (LDL)-induced incorporation of [¹⁴C]oleate into CF in cells in a dose-dependent manner. This was partly due to vitamin E Also significantly inhibiting the uptake of [³H]CE-labeled acetylated LDL by 1774 cells. A trend existed toward suppression of acyl-CoA:cholesterol acyltransferase (ACAT) activity in the cell lysate at high vitamin E concentration, but there was no effect on hydrolysis of CE. These data indicate that vitamin E reduces the uptake of modified LDL and suppresses ACAT activity, resulting in less cholesterol esterification in macrophages; a novel mechanism underlying the antiatherogenic properties of vitamin E.     

Formation Processes of β-C2S by the Decomposition of Hydrothermally Prepared C-S-H with Ca(OH)2

A mixture of CaO and silicic acid prepared with a Ca/Si ratio of 2.0 was hydrothermally synthesized at 80° to 200°C, and the thermal decomposition behavior of the products (C-S-H with Ca(OH)₂) was analyzed using XRD, ²⁹Si MAS NMR, and the trimethylsililation method (TMS). It was found that the main silicate anion structure of C-S-H was a mixture of a dimer and a single-chain polymer (larger than Si₅O₁₆) and that polymerization advanced with an increase of the synthesizing temperature. On heating, the products decomposed to form β-C₂S. It was found that the decomposition was gradual and that the-higher the temperature of hydrothermal synthesis, the lower was the temperature of the decomposition into β-C₂S. Although the decomposition proceeded to form a monomer (β-C₂S) from the polymer and dimer, this dimer was resistant to heat and did not decompose unless heated to above 400°C.     

Photoluminescence properties of porous silicon layers prepared by electrochemical etching in extremely dilute HF solutions

Dilute HF solutions with concentrations down to 0.03% have been used to obtain luminescent porous silicon (PSi) layers on p-type Si wafers. The experimental results show that with a constant etching time of 30 min, PSi layers with sufficient luminescence efficiencies can be formed for HF concentrations as low as 0.1%. Because of a significantly lowered critical current density, only very low etching current densities of  ≤0.1 mA cm⁻² can result in the formation of luminescent PSi samples in 0.1% HF solutions. A notable result is that these low etching current densities cannot be used to form luminescent PSi layers in concentrated ( ≥1%) HF solutions. The behavior of PL intensity as a function of etching current density has been analyzed over a wide range of HF concentration. The PL intensity is determined by the ratio of the etching current density to the critical current density, suggesting that the presence of silicon oxides plays an important role in the formation of luminescent Si nanostructures in PSi layers.     

Formation Mechanism and Synthesis of Apatite-Type Structure Ba2+xLa8−x(SiO4)6O2−δ

The formation process of Ba₂La₈(SiO₄)₆O₂ was clarified using thermogravimetry–differential thermal analysis (TG-DTA) and a high-temperature powder X-ray diffraction (HT-XRD) method. Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba₂La₈(SiO₄)₆O₂ was completely reacted at 1400°C and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba_{2+ x} La_{8− x} (SiO₄)₆O_2−δ crystals with x = 0–2 was attempted using a solid-state reaction.     

Characteristics of menhaden oil ethanolysis by immobilized lipase in supercritical carbon dioxide

Ethanolysis of menhaden oil was performed with 1,3-regiospecific lipase to produce diglycerides and monoglycerides containing polyunsaturated fatty acids, and fatty acid ethyl esters. Immobilized lipases like lipozyme TL-IM (Thermomuces lanuginosa immobilized on silica gel) were used for enzymatic ethanolysis. Ethanolysis was carried out in different processes (solvent free, organic solvent and supercritical fluid system) to compare the reaction rate and yield obtained by menhaden oil ethanolysis. Organic solvent (hexane) and supercritical carbon dioxide (SC-CO₂) were used as reaction medium. The reaction products were analyzed by gas chromatography (GC), thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Higher amounts of ethanol as a substrate caused substrate inhibition which dramatically decreased the reaction rate of ethanolysis. To elucidate the effect of pressure, enzymatic ethanolysis was performed in SC-CO₂ at pressures ranging from 75 to 121 bar. Enzymatic ethanolysis of menhaden oil in SC-CO₂ decreased by substrate inhibition. Reaction rate and optimum amount of ethanol used were depended on SC-CO₂ density individually. Kinetic model with substrate inhibition (dead-end inhibition) by excess ethanol was set up to measure the reaction and inhibition rates.     

Fracture Resistance Behavior of High‐Thermal‐Conductivity Silicon Nitride Ceramics

Silicon nitride ceramics were prepared from a high‐purity silicon powder doped with 2 mol% Y₂O₃ and 5 mol% MgO as sintering additives via a route of sintering of reaction‐bonded silicon nitride (SRBSN). The materials sintered at 1900°C for 3, 6, 12, and 24 h had thermal conductivities of 109, 125, 146, and 154 W/m/K, and four‐point bending strengths of 786, 676, 608, and 505 MPa, respectively. The fracture toughness values, determined by the single‐edge‐precracked‐beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m^1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively, which were similar to the results measured by the chevron‐notched‐beam (CNB) test method. The materials sintered for longer times (12 and 24 h) showed stronger R‐curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h).