Effects of Intramolecular Distance between Amyloidogenic Domains on Amyloid Aggregation

Peptide/protein aggregation is implicated in many amyloid diseases. Some amyloidogenic peptides/proteins, such as those implicated in Alzheimer’s and Parkinson’s diseases, contain multiple amyloidogenic domains connected by “linker” sequences displaying high propensities to form turn structures. Recent studies have demonstrated the importance of physicochemical properties of each amino acid contained in the polypeptide sequences in amyloid aggregation. However, effects on aggregation related to the intramolecular distance between amyloidogenic domains, which may be determined by a linker length, have yet to be examined. In the study presented here, we created peptides containing two copies of KFFE, a simple four-residue amyloidogenic domain, connected by GS-rich linker sequences with different lengths yet similar physicochemical properties. Our experimental results indicate that aggregation occurred most rapidly when KFFE domains were connected by a linker of an intermediate length. Our experimental findings were consistent with estimated entropic contribution of a linker length toward formation of (partially) structured intermediates on the aggregation pathway. Moreover, inclusion of a relatively short linker was found to inhibit formation of aggregates with mature fibril morphology. When the results are assimilated, our study demonstrates that intramolecular distance between amyloidogenic domains is an important yet overlooked factor affecting amyloid aggregation.     

Divergent Heparin‐Induced Fibrillation Pathways of a Prion Amyloidogenic Determinant

Polysaccharides and glycosaminoglycans (GAGs), particularly heparin, have been shown to directly affect fibrillation phenomena and the biological activities of amyloid proteins. We present a systematic analysis of the impact of heparin upon fibrillation of the amyloidogenic determinant of the prion protein PrP(106–126). Experimental data, including thioflavin T fluorescence, transmission electron microscopy, and circular dichroism, demonstrate that heparin induced dramatically diverging aggregation pathways of PrP(106–126). Specifically, enhanced β‐sheet formation of the prion fragment leading to fibril assemblies occurred in solutions containing low heparin/prion mole ratios, while mixtures containing a greater abundance of heparin showed almost complete inhibition of PrP(106–126) fibril formation. Based upon the experimental data we have proposed a unified model accounting for the interplay between the roles of heparin as a scaffold for nucleation and fibril growth on the one hand and as a disruptor of fibrillation through electrostatic affinity with the monomeric peptide units on the other. This study clarifies previous conflicting studies, and concludes that GAGs inhibit fibrillation and amyloid toxicity in some cases, and promote amyloidogenesis in others.     

蛋黄卵磷脂制备工艺及超临界CO_2脱蛋黄油实验研究

对用超临界CO_2萃取技术制备蛋黄卵磷脂的几种典型工艺进行了归纳、分析和比较。根据选择的工艺,对关键设备萃取器料筒进行了改进,通过正交试验,探讨了萃取压力、温度、时间、料筒层数等条件对蛋黄油脱除率的影响规律。     

质谱技术在磷脂分析中的应用研究进展

磷脂是生物膜的主要组成部分,不仅在维持细胞正常的结构和功能方面起重要作用,同时也参与细胞的信号转导和代谢。生物体内或细胞膜磷脂成分的改变与很多代谢循环和疾病的发生密切相关。因此,应用质谱技术准确分析生物体内磷脂轮廓的变化,寻找潜在的生物标志物能够为临床早期诊断、疾病监测及新药研发提供依据,对于疾病机理研究亦具有重要的价值。就近年来磷脂的质谱分析技术及其应用进行简要综述,并对磷脂组学的发展前景进行了展望。     

Extraction of Phospholipids from Structured Dry Egg Yolk

Chicken egg yolk is a concentrated source of phospholipids (PL). Extracting egg PL with high efficiency is vital to the availability and economics of this high-valued lipid product. In this study, two types of structured dry egg yolk materials, yolk flakes and pellets, were prepared. Two commonly used solvents, hexane and ethanol, were tested on the extraction of total yolk lipids including the PL. The PL fraction was obtained by the conventional cold acetone precipitation. The drum-dried yolk flakes were shown to be an ideal starting material for total lipid and PL extraction. Anhydrous ethanol can extract almost all the neutral lipids and PL with little change to the individual components of the native PL. A PL product with a purity of more than 90 % and a yield of 99 % can be prepared using this method.     

Extraction of Phospholipids from Egg Yolk Flakes Using Aqueous Alcohols

Two alcohols, ethanol and butanol, with different water contents were evaluated for phospholipids (PL) sequential extraction from drum dried egg yolk flakes. It showed that butanol was more effective in extracting total yolk lipids compared to ethanol, but the PL in the extract had the same concentration as in the original yolk total lipid. The use of aqueous ethanol of 95 and 75% resulted in lipid extracts with higher PL concentration during the initial stages of the sequential extraction. When ethanol was further diluted to a concentration of 55%, the solvent lost its PL extraction ability, and the total lipid recovery also decreased dramatically. When both the PL purity and recovery were considered, 75% ethanol was the most effective aqueous alcohol for PL extraction and enrichment from the yolk flakes. In the first stage of extraction using such a solvent, 67% of the total PL in the original yolk was recovered in a lipid fraction with a PL purity of 75%. This study identified the optimal ethanol concentration for PL extraction from dried egg yolk. With this information, the best solid:solvent ratio can be designed to extract and enrich the polar lipids from lipid-bearing materials with known moisture content using a renewable or “green” solvent, ethanol.     

用超临界二氧化碳萃取技术制备蛋黄卵磷脂的几种工艺探讨

介绍了蛋黄卵磷脂的功能用途、市场需求和生产工艺,对用超临界CO2萃取技术制备蛋黄卵磷脂的几种典型工艺进行了归纳、分析和比较,指出这些工艺产业化过程中存在的问题,并给出一些初步解决的方案。     

Transmission electron microscopy observation of vitrinite from Liddell bituminous coal treated with tetralin

To assess the suitability of transmission electron microscopy (TEM) for investigating the detailed process of coal/solvent interaction, TEM observations have been made of small blocks of Liddell vitrinite that had been treated with tetralin in an autoclave at 320 and 350 °C. In vitrinite treated at 320 °C cell cavity fillings became porous, while the walls between cell cavities remained uniform and showed no internal texture. In vitrinite particles treated with tetralin at 350 °C two zones were recognizable at the edges of the particles: a more electron-dense inner zone and a less electron-dense outer zone. Also present in these specimens were plastospheres consisting of two different materials, primary vitroplast (a more electron-dense core) and secondary vitroplast (a less electron-dense crust). Such detailed texture has not been observed with incident light microscopy, and TEM techniques provide useful information not previously obtainable.     

高位泥炭水溶性多糖的机械化学转化

在纤维素分解酶或碱存在下,用星形粉碎机处理高位苔藓泥炭,研究了该机械化学作用对泥炭中水可溶多糖级分组成的影响。由于机械化学转化,导致多糖的产率、多分散性、分子量和光密度发生了变化。机械化学处理对泥炭水溶级分中的单糖组成也有影响。     

某成型装药射流的数值模拟与射流转化率

应用LS-DYNA及示踪点处理技术,对某一球锥罩成型装药结构的射流形成过程及射流侵彻靶板过程进行了研究,获得了有效射流沿其运动方向的速度分布、头部速度、侵彻孔几何描述等多项评估射流微元性能的重要参数。计算结果表明,对于普通强度钢质目标靶,在射流侵彻靶板过程中,常规小锥角药型罩产生的有效射流为2000m/s以上的射流段,杆式射流的临界侵彻速度值为1400m/s,从而进一步得到其射流转化率为29.65%。     

Semi-indirect synthesis of LPG from syngas: Conversion of DME into LPG

Efficient conversion of dimethyl ether (DME) into liquefied petroleum gas (LPG) with a hybrid catalyst is a novel method for semi-indirect synthesis of LPG fuel from syngas. The hybrid catalysts consisting of zeolite and hydrogenation catalyst were investigated in a fixed bed reactor. Experimental results demonstrated that the hybrid catalyst consisting of (Pd/SiO₂) and USY efficiently converted DME into LPG and restrained decomposition of DME into CO and H₂. With that catalyst, the one through conversion of DME reached about 100%, almost no CO and CO₂ were produced and selectivity for LPG was more than 65%.     

Use of cyclic anhydrides to remove cholesterol and other hydroxy compounds from fats and oils

A method for removing cholesterol from animal fats has been developed based on the reaction between the hydroxyl group of cholesterol and cyclic anhydrides. The reaction forms monoesters with acyl chains having a terminal free acid group. The conversion of cholesterol into an acid derivative makes it possible to remove the cholesterol from fats by extraction with aqueous alkali. A study of the reaction in model systems showed that optimal conditions were a molar ratio of cholesterol to succinic anhydride of 1∶3 at 135°C for several hours. Acid catalysts increased the rate of the reaction, and acetic was selected not only because of its catalytic power but also because its reflux prevented the distillation of the cyclic anhydride from the reaction mixture. If all the cyclic anhydride was added at the beginning of the reaction, animal fats such as lard, tallow and milk fats were reduced in their cholesterol content by about 40%. A study of the reaction mechanism showed that the cholesterol reduction could be increased to 60–70% by altering the amount and the addition sequence of cyclic anhydride. The effectiveness of acid catalysts was related inversely to the negative logarithm of their acid dissociation constant (pK), but as their effectiveness increased, so did their tendency to form other, unwanted esters of cholesterol. A mixture of monoethyl fumarate and acetic acid sped the reaction, compared with acetic acid alone, with minimal formation of cholesteryl acetate. Studies with¹⁴C-cholesterol showed little formation of products other than cholesteryl hemiscuccinate during the reaction. The procedure removed some of the tocopherol from the fat but had no other detectable effect on fat stability. The procedure also can be used to concentrate the lactone precursors from milk fat.     

Biochemical Characterization and Complete Conversion of Coenzyme Specificity of Isocitrate Dehydrogenase from Bifidobacterium longum

Bifidobacterium longum is a very important gram-positive non-pathogenic bacterium in the human gastrointestinal tract for keeping the digestive and immune system healthy. Isocitrate dehydrogenase (IDH) from B. longum (BlIDH), a novel member in Type II subfamily, was overexpressed, purified and biochemically characterized in detail. The active form of BlIDH was an 83-kDa homodimer. Kinetic analysis showed BlIDH was a NADP⁺-dependent IDH (NADP-IDH), with a 567- and 193-fold preference for NADP⁺ over NAD⁺ in the presence of Mg²⁺ and Mn²⁺, respectively. The maximal activity for BlIDH occurred at 60 °C (with Mn²⁺) and 65 °C (with Mg²⁺), and pH 7.5 (with Mn²⁺) and pH 8.0 (with Mg²⁺). Heat-inactivation profiles revealed that BlIDH retained 50% of maximal activity after incubation at 45 °C for 20 min with either Mn²⁺ or Mg²⁺. Furthermore, the coenzyme specificity of BlIDH can be completely reversed from NADP⁺ to NAD⁺ by a factor of 2387 by replacing six residues. This current work, the first report on the coenzyme specificity conversion of Type II NADP-IDHs, would provide better insight into the evolution of NADP⁺ use by the IDH family.     

Solvent extraction of oil from soybean flour II— pilot plant and two-solvent extractions

The process of grinding soybeans to a fine flour and extracting the flour with hexane was studied on a pilot plant scale. The crude oil from the pilot plant study had 15 ppm phosphorus and was suitable for physical refining after a light acid pretreatment and bleaching. The refined oil showed a Lovibond color of 1.4 yellow and 0.3 red. The pilot plant study also showed that grinding of the soybeans and the separation of solid from miscella were the most difficult steps in solvent extraction with fine flour. A laboratory study on separation of miscella from meal by aqueous ethanol reduced the hold-up volume, but it did not remove all the miscella. A test with betacarotene showed that only the miscella outside the flour particles was displaced. Aqueous ethanol solutions used as a second solvent extracted additional nontriglyceride materials (primarily phospholipids) from the meal. Also, the free fatty acid content of the oil was increased with aqueous ethanol solution wash. The quality of the extracted crude oil was lowered by using a second solvent, but it had the advantage of needing only one centrifugation to separate miscella from meal.     

Continuous production of structured phospholipids in a packed bed reactor with lipase from <Emphasis Type="Italic">Thermomyces lanuginosa</Emphasis>

The possibilities of producing structured phospholipids between soybean phospholipids and caprylic acid by lipase-catalyzed acidolysis were examined in continuous packedbed enzyme reactors. Acidolysis reactions were performed in both a solvent system and a solvent-free system with the commercially immobilized lipase from Thermomyces lanuginosa (Lipozyme TL IM) as catalyst. In the packed bed reactors, different parameters for the lipase-catalyzed acidolysis were elucidated, such as solvent ratio (solvent system), temperature, substrate ratio, residence time, water content, and operation stability. The water content was observed to be very crucial for the acidolysis reaction in packed bed reactors. If no water was added to the substrate during reactions under the solvent-free system, very low incorporation corporation of caprylic acid was observed. In both solvent and solvent-free systems, acyl incorporation was favored by a high substrate ratio between acyl donor and phospholipids, a longer residence time, and a higher reaction temperature. Under certain conditions, the incorporation of around 30% caprylic acid can be obtained in continuous operation with hexane as the solvent. Presented at the 95th American Oil Chemists' Society Annual Meeting and Expo in Cincinnati, Ohio, May 10, 2004.     

High-performance dispersant of coal–water slurry synthesized from wheat straw alkali lignin

Environmental concerns have stimulated interest in utilizing plant-derived materials in various industrial fields. The main objective of the present study was to synthesize a new type of high-performance lignin series dispersant of coal–water slurry (CWS) from wheat straw alkali lignin (WAL), and determine the affecting factors in the reaction and the application performance for CWS preparation. The experimental results showed that the inherent viscosity and the sulfonic group content of the modified wheat straw alkali lignin (MSL) are the key factors affecting its dispersing effect for CWS. In the reaction, the reactant mass concentration and the sulfonating agent amount were changed to obtain the MSL with different inherent viscosities and sulfonic group contents, and the MSL with intermediate inherent viscosity (6.0 ml/g) and higher sulfonic group content (1.80 mmol g^− 1) was found to have excellent dispersing effect for CWS. The MSL obtained from optimized process was used as dispersant for CWS preparation, the studies of the properties of CWS showed that MSL has similar dispersing effect with naphtalenesulfonate–formaldehyde condensate, and far better dispersing effect than lignosulphonate. Recently this kind of new dispersant has been applied in several power plants in China.     

Characterization of Biomimetic Cofactors According to Stability,Redox Potentials,and Enzymatic Conversion by NADH Oxidase from Lactobacillus pentosus

Oxidoreductases are attractive biocatalysts that convert achiral substrates into products of higher value, but they are also for the most part dependent on nicotinamide cofactors. Recently, biomimetic nicotinamide derivatives have received attention as less costly alternatives to natural cofactors. However, recycling of biomimetics is still challenging because there are only limited opportunities. Here, we have characterized various biomimetic cofactors with regard to stability and redox potentials to find the best alternative to natural cofactors. Further, the cofactor spectrum of NADH oxidase from Lactobacillus pentosus (LpNox) could be expanded, and the enzymatic activity was also compared to activities with different small‐molecule catalysts. As a result, we succeeded in identifying several strategies for regeneration of oxidized biomimetics.