非晶态Ni—Si—B系合金结构驰豫的电阻法研究

本文通过精密测定非晶态Ｎｉ－Ｓｉ－Ｂ系合金的电阻率在不同温度下等时退火后的变化，研究了该合金的结构驰豫过程，得到其电阻率变化随退火温度而作振荡性起伏的关系曲线，并利用作者提出的结构缺陷形成机制对该振荡性曲线作出了比较合理的微观机理解释。     

Microbial contribution to SOM quantity and quality in density fractions of temperate arable soils

The formation of soil organic matter (SOM) very much depends on microbial activity. Even more, latest studies identified microbial necromass itself being a significant source of SOM and found microbial products to initiate and enhance the formation of long-term stabilized SOM. The objectives of this study were to investigate the microbial contribution to SOM in pools of different stability and its impact on SOM quality. Hence, four arable soils of widely differing properties were density-fractionated into free and occluded particulate organic matter (fPOM, oPOM < 1.6 g cm⁻³ and oPOM < 2.0 g cm⁻³) and mineral associated organic matter (MOM > 2.0 g cm⁻³) by using sodium polytungstate. These fractions were characterized by in-source pyrolysis-field ionization mass spectrometry (Py-FIMS). Main SOM compound classes of the fractions were determined and further SOM properties were derived (polydispersity, thermostability). The contribution of microbial derived input to arable soil OM was estimated from the hexose to pentose ratio of the carbohydrates and the ratio of C₄–C₂₆ to C₂₆–C₃₆ fatty acids. Additionally, selected samples were investigated by scanning electron microscopy (SEM) for visualizing structures as indicators for the origin of OM. Results showed that, although the samples differed significantly regarding soil properties, SOM composition was comparable and almost 50% of identifiable SOM compounds of all soils types and all density fractions were assigned to phenols, lignin monomers and alkylaromatics. Most distinguishing were the high contents of carbohydrates for the MOM and of lipids for the POM fractions. Qualitative features such as polydispersity or thermostability were not in general assignable to specific compounds, density fractions or different mean residence times. Only the microbial derived part of the soil carbohydrates could be shown to be correlated with high SOM thermostability (r² = 0.63**, n = 39). Microbial derived carbohydrates and fatty acids were both enriched in the MOM, showing that the relative contribution of microbial versus plant-derived input to arable SOM increased with density and therefore especially increased MOM thermostability. Nevertheless, the general microbial contribution to arable SOM is suggested to be high for all density fractions; a mean proportion of about 1:1 was estimated for carbohydrates. Despite biomolecules released from living microorganisms, SEM revealed that microbial mass (biomass and necromass) is a considerable source for stable SOM which is also increasing with density.     

Arg引入“Ser/Thr”平面对木聚糖酶XynⅡ热稳定性的影响

【目的】为了提高来源于宇佐美曲霉(Aspergillus usamii)的高比活木聚糖酶XynⅡ的热稳定性,对其热稳定性影响因素进行改造。【方法】对木聚糖酶XynⅡ进行同源建模和序列比较,在XynⅡ的"Ser/Thr"平面引入精氨酸的四点诱变和五点诱变,对酶的热稳定性进行改造。【结果】获得的2个突变酶在热稳定性上较野生型酶均有不同程度提高,突变酶ST4、ST5的最适温度分别由原酶的50℃提高为52和55℃。55℃保温15 min,ST4、ST5的残留酶活性由原酶的20%提高为65%和75%;保温1 h,ST4、ST5的残留酶活性由原酶的15%提高为50%和65%。【结论】突变酶ST4、ST5在保持了XynⅡ优良性质的基础上,进一步提高了其热稳定性,具有更好的应用价值。     

植酸酶耐热性评价方法的研究

植酸是畜禽常规植物性饲料中磷的主要存在形式,也是一种广谱性的抗营养因子。在饲粮中添加植酸酶来消除这种抗营养因子的不利效应、提高家禽的生产性能、降低饲料成本已成为饲料业中常用的方法。在实际应用中,饲料加工过程对添加在饲料中的植酸酶产生的不利影响是限制植酸酶进一步推广应用的重要因素。目前,市场上已有多种耐高温植酸酶产品推出,但产品对饲料制粒过程的耐受性能仍然是最受关注的焦点。因此,如何对不同的耐高温植酸酶产品进行耐热性能的评价具有重要的现实意义。文中比较了几种实验室条件下评价植酸酶耐热性的方法,并结合饲料制粒试验,结果表明,在蒸汽消毒器中利用湿热蒸汽处理的方法是一种简单、快速,并接近饲料加工过程中酶活损失情况的植酸酶耐热性评价方法。     

Heat tolerance in food legumes as evaluated by cell membrane thermostability and chlorophyll fluorescence techniques

Summary The genotypic variation for heat tolerance in chickpea, groundnut, pigeonpea, and soya bean was evaluated by testing membrane stability and photosystem (PSII) function in leaves at high temperatures. The legumes could be ranked from heat-tolerant to sensitive in the order: groundnut, soya bean, pigeonpea and chickpea. The damage to cell membranes (as reflected by an increased leakage of electrolytes) and PS II (as reflected by a decrease in the ratio of variable to maximum fluorescence) was less, and recovery from heat stress was faster in groundnut than in other crops. Prior exposure of plants to 35°C for 24h led to a reduced leakage of electrolytes at high temperatures in all crops but the differences among legumes were consistent. Substantial genotypic variation for heat tolerance was found in all legumes. Membrane injury was negatively associated with specific leaf weight in groundnut (r=–0.69^**) and soya bean (r=–0.56^**) but not in the pulses. Electrolyte leakage and fluorescence ratio were negatively correlated in all legumes. The potential use of electrolyte leakage and fluorescence tests as screening procedures for breeding heat-tolerant legumes is discussed.Abbreviations RI relative injury - Fo initial fluorescence - Fm maximum fluorescence - Fv variable fluorescence - PS II photosystem II - PAR photosynthetically active radiation     

鸡新城疫活疫苗耐热保护剂研究

应用冻干制品加速热稳定性试验,测试三组冻干保护剂配方对鸡新城疫(LaSota株)活疫苗的耐热保护效果。结果表明3号配方的耐热保护效果理想,主要表现为剩余水份含量低,37℃保存不萎缩,各种温度下保存病毒损失量低。     

Primary structure and thermostability of bigeye tuna myoglobin in relation to those of other scombridae fish

ABSTRACT:   In the present study, the cDNA encoding myoglobin (Mb) of bigeye tuna Thunnus obesus was cloned and its amino acid sequence deduced in order to investigate the relationship between the primary structure and thermostability of scombridae fish Mb. An open reading frame of bigeye tuna Mb cDNA contained 444 nucleotides encoding 147 amino acids. The primary structure of bigeye tuna Mb was highly conserved when compared with those of bluefin tuna and yellowfin tuna Mb, the sequence identity being 95.2–100.0%. It also showed relatively high identity (82.3–89.1%) with the counterparts of scombridae fish. Myoglobin was then isolated from the dark muscle of four scombridae fish including bigeye tuna. Differential scanning calorimetry and circular dichroism measurements on these Mb revealed that the thermostability of bigeye tuna Mb was lowest and that of skipjack Katsuwonus pelamis Mb highest among the scombridae fish Mb examined. The α-helical contents of scombridae fish Mb at 10°C were in the range of 39.8–44.8%, clearly lower than that of horse Mb (55.3%), suggesting instability of fish Mb. The melting temperatures of these Mb fell in the range of 75.7–79.9°C, lower than that of horse Mb (84.2°C). These results strongly suggest the instability of fish Mb.     

盐桥与全基因组微生物耐热性的关系研究

挑选了NCBI COG数据库中具有全基因组的单细胞微生物,选择其中三维结构已知的蛋白质作为研究对象,研究了盐桥数目和类型对古细菌和细菌类蛋白质耐热性的影响作用。结果表明:无论古细菌还是细菌类蛋白质,总盐桥含量和盐桥网络都随耐热性的提高而增加;古细菌类超高温蛋白质形成盐桥时对Asp的利用率比较高;细菌类耐热蛋白质形成盐桥时尽量利用带正电荷的Lys和带负电荷的Glu,而常温蛋白质尽量利用带正电荷的His和带负电荷的Asp;由于耐热蛋白质对带电荷氨基酸的利用率高,即使细菌类耐热蛋白质和常温蛋白质含有等量的带电荷氨基酸,其稳定性也会提高。     

热稳定性木聚糖酶结构模拟及分析

通过对海栖热袍菌热稳定性木聚糖酶B的结构模拟,发现它有F/10木聚糖酶家族典型的(β/α)8折叠桶结构.分析其二级结构含量,发现α-螺旋中氨基酸含量最多,占总氨基酸量的43%,是酶稳定性的一个重要原因;折叠片结构含量占总氨基酸量的16.8%,这些成分构成了酶的活性中心位点和底物结合部位,为研究热稳定性木聚糖酶奠定了基础.同时将模拟结构同后来用X-射线测定结构进行了比较,对于结构模拟有重要参考价值.     

马铃薯块茎细胞膜热稳定性的配合力与杂种优势分析

利用马铃薯栽培种亲本组配的 6× 6完全双列杂交 (包括反交 ) ,对该性状 (以相对热损伤率RI %表示 )进行配合力和杂种优势分析。结果表明 :①该性状的一般配合力效应 (GCA) ,特殊配合力效应 (SCA)和反交效应 (R)均达极显著水平。上述 3因素相对作用大小南、北马铃薯分别为 3 9∶1∶1 6和 2 1∶1∶0 5 ,说明该性状的遗传虽以加性基因效应占一定优势 ,但非加性基因效应和反效应也起重要的作用。②此性状受质核互作和 (或 )细胞质的明显影响。③一些杂种F1的细胞膜热稳定性具有明显的杂种优势 ,并存在超亲遗传现象。这将为马铃薯的耐热性遗传改良和杂种优势利用提供依据。