粘质沙雷氏菌马来酸顺反异构酶表达纯化及酶学性质

从粘质沙雷氏菌(Serratia marcescens)中扩增得到马来酸顺反异构酶基因。将该基因连接到p ET24a载体上,并在Escherichia coli BL21(DE3)中实现了成功表达。酶学性质研究表明,重组酶的比酶活力为48.01 U/mg。其最适温度为37℃,最适p H为8.4。在最适反应条件下,Km值为4.20 mmol/L,Vmax为1.27 mmol/(L·min),kcat为4.38 s-1,催化效率kcat/Km为1.04 L/(mmol·s)。研究结果进一步显示,马来酸顺反异构酶具备良好的热稳定性(55℃半衰期为1.5 h)及高达99%以上的转化率,为马来酸顺反异构酶的进一步研究和工业应用制备高纯度的富马酸提供了理论基础和支持。     

Thermostable collagenolytic activity of a novel thermophilic isolate, Bacillus sp. strain NTAP-1

We isolated an acidophilic thermophile belonging to the genus Bacillus, strain NTAP-1, which secreted a thermostable collagenolytic activity into the culture medium. The collagenolytic activity exhibited an optimum pH for Azocoll hydrolysis of pH 3.9 and was not completely inhibited by 10 mM ethylenediaminetetraacetic acid (residual activity, 63%), suggesting that Bacillus NTAP-1 produces a novel acid proteinase with highest activity for collagen. The collagenolytic activity was thermostable; more than 80% of the original activity was retained after incubation of the culture supernatant at pH 4.0 and 60 degrees C for 4 h.     

POM共聚单元的序列结构及其对热稳定性和结晶行为的影响

采用核磁共振氢谱(H-NMR)分析了几种具有代表性的聚甲醛(POM)分子链中共聚单元的序列结构特征,并考察了其序列结构与热稳定性及结晶速率的关系。结果表明,共聚单元中亚氧甲基一亚氧乙基一亚氧甲基(MEM)链段含量越小,则共聚POM耐热性越差,且在热经时处理的条件下,半结晶时间(tv2)增加越显著;随热经时处理时间变长,共聚POM的结晶速率变慢与热分解导致的—CH2—CH2—O—含量相对提高有关,而均聚POM的结晶速率变慢与热分解导致的端基含量增加有关;由各种POM分子中MEM单元含量所导致的耐热性变化与结晶速率变化的规律完全一致。     

Directed evolution converts subtilisin E into a functional equivalent of thermitase

We used directed evolution to convert Bacillus subtilis subtilisinE into an enzyme functionally equivalent to its thermophilichomolog thermitase from Thermoactinomyces vulgaris. Five generationsof random mutagenesis, recombination and screening created subtilisinE 5-3H5, whose half-life at 83°C (3.5 min) and temperatureoptimum for activity (T_opt, 76°C) are identical with thoseof thermitase. The T_opt of the evolved enzyme is 17°C higherand its half-life at 65°C is >200 times that of wild-typesubtilisin E. In addition, 5-3H5 is more active towards thehydrolysis of succinyl-Ala-Ala-Pro-Phe-p-nitroanilide than wild-typeat all temperatures from 10 to 90°C. Thermitase differsfrom subtilisin E at 157 amino acid positions. However, onlyeight amino acid substitutions were sufficient to convert subtilisinE into an enzyme equally thermostable. The eight substitutions,which include known stabilizing mutations (N218S, N76D) andalso several not previously reported, are distributed over thesurface of the enzyme. Only two (N218S, N181D) are found inthermitase. Directed evolution provides a powerful tool to unveilmechanisms of thermal adaptation and is an effective and efficientapproach to increasing thermostability without compromisingenzyme activity.     

Seasonal Expression of 2 Types of Myosin with Different Thermostability in Silver Carp Muscle (Hypophthalmichthys molitrix)

Myofibrils were prepared from dorsal muscle of silver carp monthly from Jul 2003 to Jun 2004. Myofibrils of silver carp in the summer season were much more stable than those in the winter season as measured by (Ca‐ATPase) thermal inactivation rate (k_D) at 0.1 M KCl. The k_D of myofibrils measured at 2 M KCl was referred as 1 for myosin without protection by F‐actin. It was proved that myosin itself in summer season fish (summer‐type) was very stable compared with that in winter season fish (winter‐type). Winter‐type myosin easily denatured upon storage in ice. Analysis of the thermal inactivation profiles of myosin monthly prepared demonstrated that myosins in December, January, February, and March were winter‐type, and ones in June, July, August, and September were summer‐type. It was also demonstrated that both winter‐type and summer‐type myosin at different ratios coexisted in the transit season (April, May, October, November), showing the breaking point in the inactivation profile. It was concluded that silver carp expresses 2 types of myosin with different k_D seasonally and that the exchange of the expression completed in 2 mo.     

Thermal cycling effect in Cu—11.9Al—2.5Mn shape memory alloy with high Mstemperature

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Nb-V-Ti和V-Ti微合金钢中碳氮化物的回溶行为

采用TEM和EDX技术,研究了低碳微合金钢中Nb,V,Ti的碳氮化物在不同温度保温后的回溶行为.结果表明,Nb-V-Ti微合金钢中存在尺寸明显不同的两类析出,较大的析出颗粒平均尺寸在80 nm以上,其心部为(Nb,V,Ti)(C,N),而边部为(Nb,Ti)(C,N),较小的析出颗粒平均尺寸在20 nm以下,其类型为(Nb,Ti)(C,N).两类析出物中Nb/Ti原子比均随回溶温度的升高而减小.V-Ti微合金钢中,Ti的存在对V的回溶具有拖曳作用,提高了V的碳氮化物的热稳定性.Nb-V-Ti微合金钢中,由于Nb,V,Ti之间综合作用,使得析出相中V具有更高的热稳定性.     

含有分子筛次级结构的多孔支撑体的制备及表征

以丝光沸石(MOR)分子筛为原料,采用冷等静压-固态粒子烧结法制备分子筛膜用含有MOR次级结构的多孔支撑体。分别采用氮气渗透通量、开孔孔隙率、抗压强度、平均孔径及孔径分布、热膨胀系数、X射线衍射(XRD)、拉曼(Raman)光谱、扫描电镜(SEM)等表征多孔支撑体的性能。结果表明,氮气渗透通量、开孔孔隙率随煅烧温度升高和煅烧保温时间延长而降低;抗压强度则与之相反;平均孔径随煅烧温度升高变大,孔径分布随原料粒径分布变窄而变窄;保留了原料中MOR的四、五和八元环等次级结构;次级结构的存在及较低的热膨胀系数(10-6℃-1级别)使得在其表面制备的MOR分子筛膜具有良好的耐热稳定性。     

改性羧甲基羟丙基纤维素醚热稳定性研究

通过研究纤维素醚水溶液在不同温度下的粘性行为和纤维素醚在静态空气和氮气流中的热裂解及其裂解活化能计算,探讨了改性羧甲基羟丙基纤维素醚的热稳定性。结果表明:与羧甲基羟丙基纤维素醚相比较,改性羧甲基羟丙基纤维素醚的粘度热稳定性和裂解热稳定性都有一定程度的提高。     

我国氯化石蜡的生产现状

介绍了氯化石蜡的优异性能，用途，国内外氯化石蜡的生产工艺及市场供求情况，分析了国内生产存在的主要问题。