陈皮提取物对α-葡萄糖苷酶的抑制作用研究

为了研究新会陈皮的降糖活性,首先制备了5年和10年陈皮的乙醇提取物,再使用5种不同极性溶剂进行萃取,分别得到石油醚层、二氯甲烷层、乙酸乙酯层、正丁醇层以及水层提取物。接着评估这些粗提物对α-葡萄糖苷酶的体外抑制活性。结果表明:5年和10年陈皮提取物的石油醚层对α-葡萄糖苷酶的IC_(50)均为0.2 mg/mL,二氯甲烷层的IC_(50)分别为8.3、8.7 mg/mL,乙酸乙酯层的IC_(50)分别为17.8、8.4 mg/mL,正丁醇层和水层无明显活性,阳性对照品阿卡波糖的IC_(50)为58.8 mg/mL。本研究表明,新会陈皮具有较好的α-葡萄糖苷酶体外抑制活性,具有开发成降糖功能食品的潜力,本研究为新会陈皮的深度开发提供了科学依据和参考。     

Geobacillus thermodenitrificans α-半乳糖苷酶原核表达及其酶学性质

本文利用大肠杆菌原核表达系统对来源于Geobacillus thermodenitrificans的α-半乳糖苷酶编码基因进行了重组表达,并对该酶的酶学性质进行了研究。结果表明,该α-半乳糖苷酶的分子量为100~110 kDa,以pNPG为底物时,该酶的最适反应温度为70 ℃,最适pH6.0,且该酶具有较好的温度稳定性和pH稳定性;Hg+、Ag+、Cu2+离子能完全抑制α-半乳糖苷酶的活性,Fe3+、Mn2+、Zn2+等离子对α-半乳糖苷酶的活性具有不同程度的激活作用;以pNPG为底物测得该酶的米氏常数K_m=10.04 mmol/L,最大反应速度V_max=18.25 μmol/min。     

1-脱氧野尻霉素对α-葡萄糖苷酶的抑制作用机制

运用紫外光谱法、荧光光谱法和圆二色光谱法,研究桑叶提取物1-脱氧野尻霉素（1-deoxynojirimycin,DNJ）对α-葡萄糖苷酶的作用。结果发现：DNJ与α-葡萄糖苷酶反应的半抑制浓度为0.297 μg/mL,作用类型为竞争型抑制;其与α-葡萄糖苷酶主要通过静电吸引力相互作用形成基态复合物,并使α-葡萄糖苷酶的内源荧光猝灭;DNJ与α-葡萄糖苷酶相互作用形成复合物的过程是熵驱动的吸热反应,静电吸引力是两者结合反应的主要驱动力。不同温度（273、298、310 K）条件下荧光猝灭常数（Ksv）分别为1.48×104、1.29×104、1.12×104 L/mol。DNJ使α-葡萄糖苷酶的构象发生变化,且使其二级结构重新排列;诱导酶活性口袋关闭,不利于底物结合到活性位点,推测这可能是DNJ抑制α-葡萄糖苷酶活性从而降低血糖水平的机理。     

异甘草素抑制α-葡萄糖苷酶的分子机制

α-葡萄糖苷酶活性与糖尿病患者的餐后血糖水平有重要关联,寻找食源性的α-葡萄糖苷酶抑制剂是当前功能性食品研究的热点。异甘草素是甘草的重要活性成分,相关研究表明甘草提取物具有α-葡萄糖苷酶抑制活性,推测与异甘草素有关。鉴于此,本实验通过酶抑制、荧光猝灭以及分子对接等方法研究异甘草素抑制α-葡萄糖苷酶活性的机制。结果表明,异甘草素以竞争性与非竞争性相混合的方式抑制α-葡萄糖苷酶,其抑制效果明显优于阿卡波糖。荧光猝灭分析结果表明在疏水作用力驱动下异甘草素可与α-葡萄糖苷酶结合生成复合物,结合位点数为1。分子对接结果验证了相关实验结论：异甘草素位于酶的疏水口袋中,与残基Asp202和Arg400以氢键结合,并与周围众多的疏水残基存在疏水作用,共同维持该复合物结构。本研究对于开发新型的食源性α-葡萄糖苷酶抑制剂、推动异甘草素在功能性食品和医药领域的应用具有一定的参考意义。     

Nutrient digestibility,ruminal fermentation,and milk yield in dairy cows fed a blend of essential oils and amylase

Two experiments were carried out to evaluate a blend of essential oils (EO) combined with amylase as an alternative to ionophores and its potential for reducing the use of antibiotics in the dairy industry. In experiment 1, 8 rumen-cannulated Holstein cows (576 ± 100 kg of body weight, 146 ± 35 d in milk, and 35.1 ± 4.0 kg/d of milk yield at the start of the experiment) were assigned to a 4 × 4 Latin square experiment with 21-d periods to determine the influence of feed additives on total apparent digestibility of nutrients, ruminal fermentation, N utilization, microbial protein synthesis, blood glucose and urea concentrations, and milk yield and composition in dairy cows. Treatment sequences assigned to cows in each block included no feed additives (control; CON); monensin (MON) added at 13 mg/kg of diet dry matter (DM); a blend of EO supplemented at 44 mg/kg of diet DM; and EO treatment combined with α-amylase at 330 kilo novo units/kg of diet DM (EOA). Differences among treatments were studied using orthogonal contrasts as follows: CON versus feed additives (MON, EO, and EOA), MON versus EO and EOA, and EO versus EOA. No differences were detected in nutrient intake and digestibility in cows. In general, feed additives decreased ruminal NH₃-N concentration of cows, notably when diet was supplemented with MON. Furthermore, feed additives increased ruminal concentrations of acetate, butyrate, and branched-chain fatty acids. Cows fed treatments containing EO and EOA exhibited lower pH, higher NH₃-N, and a trend to greater total volatile fatty acid concentration in the ruminal fluid compared with cows fed MON. Treatments containing EO increased ruminal butyrate concentration compared with MON. No treatment × time interaction effect was observed on ruminal fermentation measurements. Cows fed diets supplemented with feed additives had greater efficiency of N transfer into milk (milk N:N intake), whereas cows fed EOA exhibited greater N transfer into milk than those fed EO. Treatments had no effect on milk yield and composition, but feed additives increased the milk yield efficiency (milk yield divided by dry matter intake), whereas treatments containing EO had similar milk yield efficiency compared with MON. For experiment 2, 30 multiparous Holstein cows (574 ± 68 kg of body weight, 152 ± 54 d in milk, and 30.9 ± 4.1 kg/d of milk yield at the start of the experiment) were enrolled to a randomized complete block design experiment. The MON, EO, and EOA treatments were randomly assigned to cows within blocks (n = 10), and feed additives were provided throughout a 9-wk period. No differences were found in nutrient intake and digestibility, but cows fed EOA tended to exhibit greater dry matter intake than those fed EO. Blood metabolites and milk production were not affected by treatments. However, cows fed MON or EOA had greater milk protein content than those cows fed treatments containing EO. Feeding EO with or without amylase had similar response to feeding MON in terms of feed intake and milk yield, with a small negative effect on milk protein yield when feeding EO alone. Feed additives increased the concentrations of acetate, butyrate, and branched-fatty acids in ruminal fluid, whereas treatments containing EO had greater ruminal butyrate and NH₃-N concentrations. Therefore, either EO or EOA can replace MON in diets of dairy cows while maintaining performance.     

菌株F21来源α-淀粉酶的酶学性质研究

该研究对菌株F21所产的α-淀粉酶进行纯化和酶学性质研究。 通过硫酸铵盐析、疏水层析等方法纯化后,α-淀粉酶酶活达到 4 616.3 U/mL。 酶学性质研究表明,该酶最适pH值为4.8,最适温度为55 ℃,且酶在pH 4.0～9.0及低于45 ℃的条件下稳定性较高;Ca2+ 对酶活有较强激活作用,Fe2+及Fe3+对酶活有较强的抑制作用。     

Effect of H2 flow rate and stand-off distance on the formation of phases in plasma-sprayed Al2O3 coatings

Plasma-sprayed Al₂O₃ coatings contain both metastable and stable phases of Al₂O₃. The formation of these phases is influenced by various process parameters, such as stand-off distance (SOD), gas flow rates, nozzle diameter and is also dependent on the melting and solidification behaviour of feedstock particles, as these help in controlling the weight fraction of different phases formed in the coating. The present work reports the investigation on the effect of two major plasma spray parameters, namely secondary gas (H₂) flow rate and SOD, on the formation of phases in plasma-sprayed Al₂O₃ coating. The phases were identified by X-ray diffraction analysis and to quantify those phases, the Rietveld refinement method was used. The influence of α-phase on the mechanical properties of the Al₂O₃ coatings was evaluated, and it has been observed that α-phase content decreases with the increase in secondary gas flow rate. With the increase in SOD, the α-Al₂O₃ phase content first decreases and then increases.     

α-Fe2O3光电催化分解水研究进展

利用光电催化技术分解水制氢来获得清洁能源,有助于缓解当前化石能源日益萎缩及二氧化碳排放污染环境带来的压力。α-Fe_2O_3具有带隙合适、化学稳定性好、资源丰富以及经济可行性好等特点,使其在光电极材料研究中一直备受青睐。但是,由于氧化铁材料导电性差,光生电子和空穴复合率高等原因,限制了该材料在光电催化技术中的发展应用。从光阳极材料分解水制氢的原理出发,综述了近年来通过形貌控制如制备多层薄膜、纳米管(核壳结构的纳米棒)及纳米网等,引入Sn、Si、Ti、Mn、Al、Zn等元素以及部分元素的共掺杂,引入氧空位及与IrO_2、Co-Pi、Al_2O_3、石墨烯等其他材料的复合等几种途径,促进光生载流子的迁移效率,减少载流子的复合机率,进一步提高光电流密度并降低起动电压,以达到改善α-Fe_2O_3性能的研究工作。     

α-Glucosidase and α-amylase inhibitors from seed oil: A review of liposoluble substance to treat diabetes

One of the effective managements of diabetes mellitus, in particular, noninsulin-dependent diabetes mellitus, is to retard the absorption of glucose by inhibition of carbohydrate hydrolyzing enzymes, such as α-glucosidase and α-amylase, in the digestive organs. Currently, there is renewed interest in plant-based medicines and functional foods modulating physiological effects in the inhibition of α-glucosidase and α-amylase. Accordingly, inhibitors of α-glucosidase or α-amylase derived from various sources have also been isolated, and majority of phenolic compounds and their effects have been investigated in animals as well. As such, when the presence of α-glucosidase inhibitor in many foodstuffs was screened for, we found that vegetable seed oil also strongly inhibited α-glucosidase and α-amylase. Seed oil is an important source of liposoluble constituents with potential for inhibition of these enzymes, hence can also be used as therapeutic or functional food sources. Therefore, this review is aimed at highlighting the main liposoluble classes of α-glucosidase and α-amylase inhibitors, but it is not intended to be an exhaustive review on the subject.