Effect of the solvent on the conformational behavior of the alanine dipeptide deduced from MD simulations

In general, peptides do not exhibit a well-defined conformational profile in solution. However, despite the experimental blurred picture associated with their structure, compelling spectroscopic evidence shows that peptides exhibit local order. The conformational profile of a peptide is the result of a balance between intramolecular interactions between different atoms of the molecule and intermolecular interactions between atoms of the molecule and the solvent. Accordingly, the conformational profile of a peptide will change upon the properties of the solvent it is soaked. To get insight into the balance between intra- and intermolecular interactions on the conformational preferences of the peptide backbone we have studied the conformational profile of the alanine dipeptide in diverse solvents using molecular dynamics as sampling technique. Solvents studied include chloroform, methanol, dimethyl sulfoxide, water and N-methylacetamide. Different treatments of the solvent have been studied in the present work including explicit solvent molecules, a generalized Born model and using the bulk dielectric constant of the solvent. The diverse calculations identify four major conformations with different populations in the diverse solvents: the C₇^eq only sampled in chloroform; the C₅ or extended conformation; the polyproline (PII) conformation and the right-handed α-helix conformation (α_R). The results of present calculations permit to analyze how the balance between intra- and intermolecular interactions explains the populations of the diverse conformations observed.     

营养因子对大肠杆菌发酵产转氨酶的影响

运用“单一组分缺失法”研究了18种氨基酸,11种维生素,8种微量元素,4种嘌呤与嘧啶对大肠杆菌A5发酵产转氨酶的影响。结果表明,L-甲硫氨酸是菌体生长与产酶所必需的物质,L-缬氨酸、L-异亮氨酸和L-谷氨酸分别对菌体生长和酶转化得率的提高有显著的促进作用。在此基础上构建了一个改良的合成培养基,其组成为(g/L):葡萄糖20,(NH4)2SO45,MgSO40.5,NaCl0.5,K2HPO40.5,KH2PO40.5,氨基酸混合液(包括L-Met、L-Val、L-Ile、L-Glu)0.6,pH7.2,所产转氨酶的转化得率达到72.4%。     

D-柠檬烯对大鼠酒精性肝损伤脂质代谢紊乱的影响

探讨D-柠檬烯（D-limonene）对大鼠酒精性肝损伤脂质代谢紊乱的保护作用及可能作用机制,利用持续酒精灌胃的方法建立大鼠酒精肝损伤模型,分为A、B、C、D、E、F、G共7 组。A组为空白对照组,每日给予蒸馏水灌胃,前2 周8 mL/（kg·d）,后4 周12 mL/（kg·d）;B组为酒精模型组,每日灌胃体积分数为50%的乙醇,前2 周8 mL/（kg·d）,后4 周12 mL/（kg·d）;C、D、E组分别为D-柠檬烯低、中、高剂量组,每日分别灌胃D-柠檬烯100、200、400 mL/（kg·d）,其中D-柠檬烯与A、B组等量的50%的乙醇混合后灌胃;F组为水和D-柠檬烯空白高剂量组,每日给予D-柠檬烯400 mL/（kg·d）;G组为甘利欣药物对照组,灌胃量200 mL/（kg·d）。HE染色和电镜观察肝组织形态结构和肝组织超微结构的变化,测定血清谷丙转氨酶（alanine transaminase,ALT）、谷草转氨酶（aspartate transaminase,AST）、碱性磷酸酶（phosoporic acid,ALP）、胆碱酯酶（cholinesterase,CHE）、甘油三酯（triglyceride,TG）、胆固醇（cholesterol,CHO）、低密度脂蛋白胆固醇（low densitylipoprotein-cholesterol,LDL-C）水平。结果电镜下观察到A组肝细胞结构正常,核呈圆形或椭圆,线粒体形态正常。B组肝细胞次级溶酶体数量增加,线粒体形状不规则,脂滴多。C组可见少量脂滴,高尔基体正常,线粒体清楚。D组少量脂滴,胆小管有内容物,线粒体正常。E组线粒体高尔基体正常,少量脂滴,核圆。F组细胞器无异常,少量脂滴。G组少量脂滴,偶见溶酶,体线粒体正常。B组大鼠血清ALT、AST、ALP、CHE、TG、CHO、LDL-C均高于空白对照组,差异显著（P＜0.05）;F组大鼠血清所测各指标与空白对照组无明显差异;而D-柠檬烯低、中、高剂量干预组和酒精模型组比较,血清所测各指标水平均有不同程度地降低,其中D-柠檬烯中、高剂量干预组血清所测各指标水平明显低于酒精模型组,差异显著（P＜0.05）。结论：过量酒精摄入引起的肝组织超微结构病理损伤与升高血清ALP、CHE、ALT、AST、TG、CHO、LDL-C水平,在D-柠檬烯干预下有所减轻和降低。因此,D-柠檬烯可调节过量酒精摄入造成的脂质代谢紊乱。     

Alanine : glyoxylate aminotransferase of Saccharomyces cerevisiae-encoding gene AGX1 and metabolic significance

Alanine : glyoxylate aminotransferase is one of three different enzymes used for glycine synthesis in Saccharomyces cerevisiae. The open reading frame YFL030w (named AGX1 in the following), encoding this enzyme, was identified by comparing enzyme specific activities in knockout strains. While 100% activity was detectable in the parental strain, 2% was found in a YFL030w::kanMX4 strain. The ORF found at that locus was suspected to encode alanine : glyoxylate aminotransferase because its predicted amino acid sequence showed 23% identity to the human homologue. Since the YFL030w::kanMX4 strain showed no glycine auxtrophic phenotype, AGX1 was replaced by KanMX4 in a Delta GLY1 Delta SHM1 Delta SHM2 background. These background mutations, which cause inactivation of threonine aldolase, mitochondrial and cytosolic serine hydroxymethyltransferase, respectively, lead to a conditional glycine auxotrophy. This means that growth is not possible on glucose but on ethanol as the sole carbon source. Additional disruption of AGX1 revealed a complete glycine auxotrophy. Complementation was observed by transformation with a plasmid-encoded AGX1.     

Thermochemical Study on Ternary Solid Complex of La（Gly）2（Ala）3Cl3·2H2O（s）

The complex of lanthanum chloride with Glycine and Alanine,La(Gly)2(Ala)3Cl3·2H2O,was synthesized and characterized by IR,elementary analysis,thermogravimetric analysis,and chemical analysis.The dissolution enthalpies of LaCl3 ·7H2O(s),2Gly(s) 3Ala(s)and La(Gly)2(Ala)3Cl3 ·2H2O(s)were determined in 2 mol·L-1 HCl by a solution-reaction isoperibol calorimeter.By designing a thermochemical cycle in terms of Hess' Law and through calculation,the reaction enthalpy of lanthanum chloride seven-hydrate with Glycine and Alanine was obtained:ΔrHθm(298.15 K)=(29.652±0.504)kJ·mol-1,and the standard enthalpy of formation of La(Gly)2(Ala)3Cl3·2H2O(s)ΔfHθm [La(Gly)2(Ala)3Cl3·2H2O,s,298.15 K]=-4467.6±8.3 kJ·mol-1.     

Digestion and protein metabolism of Trogoderma granarium (Coleoptera: Dermestidae) fed on different barley varieties

The Khapra beetle, Trogoderma granarium Everts, is one of the most important pests of grains which rapidly infests durable stored products in hot and dry conditions. In the current study, effects of omit ten varieties of barley (Abidar, Bahman, Line20, Line22, Line30, Lisivi, Lokht11, Makuyi, Sahand and Sahraa) were determined on digestive enzymes and protein metabolsim of T. granarium larvae under laboratory conditions as 33 ± 1 °C, 65 ± 5% RH and photoperiod of 14:10 (L: D) h. The highest and the lowest activities of α-amylase were observed in T. granarium larvae fed on Line30 and Lisivi varieties, respectively but the glucosidases showed the highest activities followed by feeding on Lokht 11. Also, the latter variety caused the highest lipase activity in the larvae while Abidar, Line20, Lisuei and Sahand imposed the lowest lipase activity. The highest activities of serine proteases including trypsin, chymotrypsin and elastase were detected in the larvae fed on Line 30 but the two exopeptidases, amino- and carboxypeptidases, showed the highest activities when the larvae fed on Lisuei. All the three aminotransferses had the highest activities in the larvae fed on Lokht 11 as the related individuals contained the maximum amount of protein compared to other ones. Results of the current study highlighted Line30 as the most suitable variety to be digested by serine proteases and α-amylase but Lokht11 is appropriately digested by glucosidases and lipase which emboss their susceptibilities to T. granarium. Our findings on digestion and protein metabolism imply on susceptibility of varieties Line30 and Lokht11 to T. granarium larvae.     

Taurine ameliorates alcoholic steatohepatitis via enhancing self-antioxidant capacity and alcohol metabolism

Chronic alcohol consumption or alcohol abuse is the main cause of alcoholic steatohepatitis or further cirrhosis. This study was to exam if the antioxidant capacity and alcohol metabolism in livers of chronic alcohol-fed rats were improved by supplementing taurine (Tau). Rats were randomly divided into four groups with five times per week of treatment: 1) isocaloric solution; 2) 3 g alcohol/kg BW/day; 3) 3 g alcohol/kg BW/day + 1 g taurine (Tau)/kg BW/day; and 4) 3 g alcohol/kg BW/day + 2 g Tau/kg BW/day. A 6-week alcohol consumption resulted in lower (p < 0.05) body weight gain and self-antioxidant capacities, as well as increased (p < 0.05) liver size, serum/hepatic lipids, and AST and ALT values. However, alcohol-fed rats co-treated with Tau have decreased (p < 0.05) liver lipid levels via increasing fecal lipid output and cholesterol metabolism. Besides, co-treatment of Tau also enhanced (p < 0.05) self-antioxidant capacities and alcohol metabolism in livers via enhancing GSH contents, CAT, GSH-Px, ADH, and ALDH activities, but decreasing MDA contents. In a histological examination of rat liver, microvesicular steatosis and necrotic cells were observed in alcohol-fed rats without Tau while largely suppressed microvesicular steatosis and no necrotic cells were observed in alcohol-fed rat supplemented with Tau. Therefore, Tau could be an effective hepatoprotective agent against alcohol-induced damage via enhancing self-antioxidant capacity and alcohol metabolism.     

太明清对扑热息痛致小鼠肝损伤的保护作用

本研究对韩国传统饮品太明清(TMC)对扑热息痛所致小鼠肝损伤的保护作用进行了研究,ICR小鼠连续14 d灌胃给予低(100 mg/kg)、中(250 mg/kg)、高(500 mg/kg)三个剂量的太明清及阳性药物水飞蓟素(100 mg/kg)后,腹腔注射扑热息痛(800mg/kg)建立动物急性肝损伤模型,动物处死后取血液和脏器测定各项指标。相对于模型对照组,太明清实验组的肝指数明显降低。三个剂量的太明清均明显降低血清谷丙转氨酶(ALT),谷草转氨酶(AST),碱性磷酸酶(ALP),甘油三酯(TG),尿素氮(BUN)水平,提高血清总胆固醇(TC),白蛋白(ALB)水平(p0.05)。且三个剂量呈现了一定的量效关系。其中太明清高剂量组对小鼠肝损伤的保护效果最佳,仅次于阳性药物水飞蓟素组(p0.05)。另外,从小鼠肝脏病理图来看,相对于模型对照组,太明清实验组对炎症及肝细胞坏死有明显改善。可见太明清对扑热息痛所致小鼠肝损伤具有较好的保护作用。     

提高工业辐照剂量测量准确度的研究

基于丙氨酸/ESR剂量测量技术，利用LAEA/IDAS剂量核验提供服务，对保证辐照产品质量和促进幅照加工产业化发挥了重要作用。本文研究和讨论了剂量核验技术，它涉及基本概念、模体、误差、剂量水平和在剂量核验中质量控制的技术细节。