醋酸木质素结构特性及抗氧化研究

采用醋酸法提取大叶麻竹笋笋壳中木质素,对其表面微观特性、结晶特性、热稳定性和吸湿特性等进行分析,并进一步研究了醋酸木质素的抗氧化能力,并与相同来源的纤维残渣和粗膳食纤维进行对比研究。研究结果表明：醋酸木质素表面成球形且结构粗糙多孔;并以无定形结构存在;热稳定性较好;吸湿率很低;在DPPH自由基清除能力和亚铁离子还原能力（FRAP）方面,醋酸木质素抗氧化能力高于人工合成的抗氧化剂BHT,其ABTS自由基清除能力与BHT相当,无显著差异。而且醋酸木质素的抗氧化能力都要显著高于相同来源的纤维残渣和粗膳食纤维。因此,醋酸木质素具有应用于抗氧化剂的潜力。     

Preparation,Characterisation and Performance of Microencapsulated Red Phosphorus

Microencapsuled red phosphorus (MRP), with a phenolic resin coating layer, was successfully prepared. It was characterized by Fourier‐transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). Meanwhile its water absorption, thermostability, thermodynamic properties and critical ignition temperature (T _b) have been studied. The results show that the MRP which is coated with phenolic resin can decrease the water absorption, increase thermostability and critical ignition temperature (T _b) significantly, compared with red phosphorus (RP). The thermodynamic properties which include apparent activation energy (E ), pre‐exponential factor (A ), activation entropy (ΔS ^#), activation enthalpy (ΔH ^#) and Gibbs free energy (ΔG ^#) of RP and MRP are obtained. Moreover, the MRP can reduce the water absorption and friction sensitivity of red phosphorus smoke agent significantly with the best content of phenolic resin is 0.5 % or 1 %.     

PtTi阻挡层对AuTi／AuGe：Ni／GaAs系统热稳定性及欧姆接触特性的影响

用俄歇电子能谱和电阻测试法研究了ＰｔＴｉ阻挡层与ＡｎＴｉ／ＡｕＧｅ：Ｎｉ／ＧａＡｓ系统热稳定性的影响及欧姆接触特性的退化。结果表明，系统在２５０℃以下热处理是稳定的，它具有良好的欧姆接触特性；在更高的温度下，发现阻挡层下面的Ｔｉ扩散穿过接触层并消耗接触层的ＧａＡｓ，在欧姆接触层下形成Ｔｉ－Ｇａ－Ａｓ／ＧａＡｓ接触。接触电阻Ｒｃ迅速增加，由原始的几欧增大到几百欧。在３２０℃热处理时，系统的欧姆接触消失变成整流接触特性。这是由于系统存在着非理想配比界面区而造成的。     

枯草芽孢杆菌植酸酶基因在大肠杆菌中的表达及其对酶热稳定性的影响

采用PCR法,获得不含有信号肽序列的来源于枯草芽孢杆菌的植酸酶phyC基因的非融合和融合表达片段,分别构建带有T7lac启动子的大肠杆菌的植酸酶pET30NFphyC和pET30FphyC表达载体,并转入大肠杆菌BL21(DE3)。大肠杆菌分别在30℃和25℃经IPTG诱导后实现了植酸酶的表达,非融合和融合植酸酶的表达量分别约占菌体总蛋白的13％和15％,分子量分别为40．13kDa和43．27kDa。表达产物具有植酸酶的生物学活性,非融合植酸酶和融合植酸酶的最适反应温度分别为50℃和75℃,经90℃处理10min,残留酶活性分别为37℃时的31．9％和75．7％。分析表明,含13个氨基酸残基的融合片段有助于植酸酶的表达和酶热稳定性的提高。     

Asp238→Asn Creates a Novel Consensus N‐Glycosylation Site in Aspergillus awamori Glucoamylase

A single mutation, Asp238→Asn (D238N), of Aspergillus awamori glucoamylase (GA) was identified that increases extracellular production of the enzyme in Saccharomyces cerevisiae at 37 °C. The mutant was isolated as a suppressor of Gly396→Ser (G396S), a previously isolated temperature‐sensitive mutation that decreases the thermostability and extracellular production of GA expressed in S. cerevisiae. Culture supernatants of the double mutant G396S/D238N contained much more GA than supernatants of G396S at 33.5 and 37 °C but not at 30 °C. Additionally, culture supernatants of the D238N contained 1.5 to 2‐fold more GA than supernatants of wild‐type when grown at 37 °C but not at 30 or 33.5 °C. The D238N mutation creates a consensus N‐glycosylation site in GA. Mass spectrometry showed that the molecular weight of D238N was 2319 Da greater than that of the wild‐type GA and that of D238N/G396S was 3094 Da greater than that of G396S, suggesting the presence of an additional N‐linked glycan at residue 238. No difference in thermostability or activity was observed between the G396S and G396S/D238N mutants or between wild‐type and D238N GAs, and D238N did not affect intracellular GA levels at 30 or 37 °C.     

Enhancement of the thermostability and activity of mesophilic Clostridium cellulovorans EngD by in vitro DNA recombination with Clostridium thermocellum CelE

The thermal stability and catalytic activity of endoglucanase (EngD) from mesophilic Clostridium cellulovorans were improved by evolutionary molecular engineering. Thermostable mutants were isolated after staggered extension process (StEP) with celE from thermophilic Clostridium thermocellum performed to conduct family shuffling and overlay screening of the resultant mutant library. The relative activity of the best-evolved clone has been improved of about 2 times higher at 50 °C and showed a higher k_cat/K_m value than its engD parental clone. We determined that these variants had two amino acid substitutions (L157N, Q158E) and confirmed their effects by substituting these amino acids in the parental gene by site-directed mutagenesis. These substitutions resulted in an increase in hydrophilic or charged residues. Our results demonstrate that in vitro recombination is an effective approach to improve the thermostability and enzymatic activity of a mesophilic enzyme.     

Development and characterization of flexible heating fabric based on conductive filaments

Active heating garments will be a promising product for improving life quality of rheumatisants and old people in the future. This paper presented an improved fabrication method of flexible heating fabrics (FHFs) which were developed by weaving intermittently silver filaments (SFs) or coated silver yarns (CSYs) into plain fabrics, this method can control more easily density of conductive filaments and rated power of FHFs in terms of requirements. Resistance thermostability and utmost load current of several kinds of conductive materials were utilized to determine an appropriate conductive material of FHFs. Subsequently, performances of FHF with SFs were characterized by a temperature controlling and power measuring device that was developed in our laboratory. Experimental results show SF can load over 0.3 A current, but the CSY and coated silver knitted fabric (CSKF) can load less than 0.1 A current. However, resistance variation ratios (RVRs) of SF are less than etc. 1.66%, but the RVRs of CSY and CSKF exceed 10% and 20%, when environment temperature increases from room temperature to 80 and 100 °C. Furthermore, strong positive linear correlations are between rated power and utmost ascending temperature of FHFs and between power consumption and presetting equilibrium temperatures of FHFs. In general, measurement data and analysis results can provide help for the design and prediction of physical properties of FHFs.     

Purification and characterization of the oxygen-thermostable hydrogenase from the aerobic hyperthermophilic archaeon Aeropyrum camini

Aeropyrum camini that was isolated from a deep-sea hydrothermal vent chimney, possessed two hydrogenases (161 and 85 kDa) in its soluble fraction. The 85-kDa hydrogenase was purified to homogeneity using several chromatography columns. The specific activities of the purified hydrogenase were: 14.8 μmol methyl viologen^ox/mg/min for hydrogen oxidation, and 14.6 μmol methyl viologen^red/mg/min for proton reduction. The oxygen stabilities of hydrogenases that were purified from A. camini and the hydrogen thermophilic bacterium Persephonella hydrogeniphila, were compared. The hydrogenase purified from P. hydrogeniphila completely lost its activity following a 96-h exposure to atmosphere; however, the A. camini hydrogenase maintained 75% of its initial activity, even after a 168 h of atmospheric exposure. A. camini hydrogenase showed a half-life of 48 h at 90 °C, while P. hydrogeniphila hydrogenase showed complete denaturation after a 30 min incubation at the same temperature. Nine residues of the N-terminal amino acid sequence of A. camini hydrogenases (MARLLMIPGT) correspond to the protein sequence encoded by the hypothetical soluble hydrogenase subunit gene (APE2423) from A. pernix strain K1. A. camini hydrogenase has a high thermostability and is very tolerant to oxygen; therefore, it may be used for actual H₂ production.     

Purification and characteristics of trypsins from cold-zone fish,Pacific cod (Gadus macrocephalus) and saffron cod (Eleginus gracilis)

Trypsins from the pyloric ceca of Pacific cod (Gadus macrocephalus) (GM-T) and saffron cod (Eleginus gracilis) (EG-T) were purified by gel filtration on Sephacryl S-200 and Sephadex G-50. The final enzyme preparations were nearly homogeneous on SDS–PAGE and the molecular weights of both enzymes were estimated to be approximately 24 kDa by SDS–PAGE. The specific trypsin inhibitors, soybean trypsin inhibitor and TLCK, strongly inhibited the activities of GM-T and EG-T. The optimum pH and optimum temperature of both trypsins were around pH 8.0 and 50 °C, respectively, using N^α-p-tosyl-l-arginine methyl ester as substrate. The GM-T and EG-T were unstable above 30 °C and below pH 5.0, and they were stabilised by calcium ion. The N-terminal amino acid sequences of GM-T (IVGGYECTRHSQAHQVSLNS) and EG-T (IVGGYECPRHSQAHQVSLNS) were found. The percentage of hydrophobic amino acid in the N-terminal 20 amino acids sequences of these cold-zone fish trypsins was lower (28%) than those of temperate-zone fish trypsins (34%), tropical-zone fish trypsins (37%) and mammalian trypsins (34%). Whereas the content of charged amino acids in the GM-T and EG-T was relatively higher than those of trypsins from temperate-zone fish, tropical-zone fish and mammals. Moreover, the GM-T catalyzed synthesis of N^α-(tert-butoxycarbonyl)-l-alanyl-l-alanine-p-nitroanilide (N^α-Boc-l-Ala-l-Ala-pNA) has been studied by using N^α-(tert-butoxycarbonyl)-l-alanine-p-guanidinophenyl ester [N^α-Boc-l-Ala-OpGu (inverse substrate)] as acyl donor and l-alanine-p-nitroanilide (l-Ala-pNA) as acyl acceptor, respectively.     

Thermostability of genetically modified sunflower oils differing in fatty acid and tocopherol compositions

The objective of the study was to investigate the performance at frying temperature of a new sunflower oil with high content of oleic and palmitic acid (HOHPSO) and containing γ‐tocopherol as the most abundant natural antioxidant. HOHPSO either containing α‐ or γ‐tocopherol (HOHPSO‐α and HOHPSO‐γ, respectively) were obtained from genetically modified sunflower seeds and refined under identical conditions. The oil stability against oxidation, as measured by Rancimat at 120 °C, was much higher for the oil containing γ‐tocopherol, suggesting the higher effectiveness of γ‐tocopherol as compared to α‐tocopherol to delay oxidation. Experiments at high temperature (180 °C) simulating the conditions applied in the frying process clearly demonstrated that, for the same periods of heating, the oil degradation and the loss of natural tocopherol were significantly lower for the oil containing γ‐tocopherol. Comparison of different genetically modified sunflower oils with different fatty acid compositions confirmed that oil degradation depended on the fatty acid composition, being higher at a higher degree of unsaturation. However, the loss of tocopherol for a similar level of oil degradation was higher as the degree of unsaturation decreased. Overall, the results showed that HOHPSO‐γ had a very high stability at frying temperatures and that mixtures of HOHPSO‐α and HOHPSO‐γ would be an excellent alternative to fulfill the frying performance required by the processors and the vitamin E content claimed by the consumers.