水溶性有机溶剂对Fe3O4磁性纳米粒子过氧化物酶样活性的影响

采用化学共沉淀法合成10nm的Fe3O4磁性纳米粒子(MNPs)。以辣根过氧化物酶(HRP)为对照,研究了四氢呋喃、1,4-二氧六环、丙酮、N,N-二甲基酰胺、甲醇和二甲亚砜等6种水溶性有机溶剂对Fe3O4MNPs过氧化物酶样活性的影响。结果表明,在有机溶剂浓度(V/V)为30%～75%时,Fe3O4MNPs相对酶活力迅速下降至近于完全失活。在15%有机溶液中,Fe3O4MNPs的最适反应温度多为50oC,最适反应pH在3.6左右。经15%有机溶液处理后的水相反应酶活显示,Fe3O4MNPs表现出对有机溶剂较强的热稳定性和pH稳定性,且对75%有机溶液也具有良好的稳定性。以上多数性质均优于相同条件下的HRP组,表明Fe3O4MNPs是一种比HRP对水溶性有机溶剂更稳定的过氧化物酶。由于Fe3O4MNPs具有易制备、成本低、易于磁分离和可循环使用的特点,因此其具有替代HRP用于有机催化的应用潜力。     

耐有机溶剂脂肪酶的研究进展

脂肪酶是一种重要的酶,在有机介质中脂肪酶能催化某些特定的化学反应。获得具有较高催化活性的耐有机溶剂脂肪酶具有重要的价值。该文概述了一些具有代表性的耐有机溶剂脂肪酶,介绍了耐有机溶剂脂肪酶的特性和应用,并对耐有机溶剂脂肪酶的筛选途径和分子改造方法进行了分析。今后有机溶剂耐受性脂肪酶的研究将集中在酶的利用、微生物筛选、脂肪酶表征和基因克隆、酶的分子改造等方面。     

有机溶剂对缢蛏碱性磷酸酯酶分子构象和催化活力的影响

本文初步研究了三种有机溶剂甲醇、二甲基甲酰胺、二氧六环对缢蛏碱性磷酸酯酶(ALP)分子构象和催化活力的影响。发现在有机溶剂作用下,ALP的荧光发射光谱、紫外差光谱、园二色光谱都发生了显著的变化,而酶经甲醇、二甲基甲酰胺预处理后酶活力提高,经二氧六环预处理后活力下降,但当测活体系中有三种有机溶剂存在时,酶的活力却被大大抑制。     

非水介质中的酶催化

传统理论认为,酶作为生物催化剂,在体外只能在水溶液环境才保持活性,而有机溶剂中酶则往往变性或失活。然而人们发现事实并非如此。如向酶溶液中加入能与水互溶的酒精、丙酮等,或制作乳化的酶水有机溶剂两相系统,甚至在几乎无水的有机介质中,酶仍能够具有催化活性。...     

有机介质中酶催化反应体系的构建原则

构建有机介质中的酶反应体系必须考虑四种物理化学原则,即有机溶剂的选择,体系中酶和有机溶剂的分配形式,酶分子的存在状态和酶的选择。     

有机溶剂对脂肪酶LipozymeIM催化活性的影响

脂肪酶LipozYmeIM经有机溶剂浸泡处理后活性显著提高。该文系统地探讨了有机溶剂特性、有机溶剂水含量以及有机溶剂浸泡温度和浸泡时间对LipozymeIM催化活性的影响。发现LipozymeIM经疏水性较强的有机溶剂浸泡处理后活性成倍增长;浸泡的最佳温度为60℃左右;浸泡时间对酶活影响不大;随着有机溶剂水含量的增加,酶活性急剧下降。     

产β-葡萄糖苷酶的菌种的筛选,鉴定及其酶学特性

β-葡萄糖苷酶来源广泛,几乎存在于所有的生物体中,而不同来源的β-葡萄糖苷酶其性质也各不同.本文利用七叶苷分离培养基从土样中分离筛选出产6种β-葡萄糖苷酶时间较快的菌种,其中发现菌种WGEA1酶活性较高,随后对菌种WGEA1进行初步的鉴定并且采用DNS法测该菌株所产粗酶液的酶学特性.酶学特性表明,WGEA1产的β-葡萄糖苷酶最适温度是在50~55℃之间,最适pH在6~7之间;在低于50℃条件下,pH为5~8时,酶活较稳定,同时在最适反应时间30 min下,金属离子和有机溶剂都对酶活性影响很大,这些发现都为在非水相体系中酶法合成烷基糖苷奠定了一定的基础.     

醋酸酐对太平洋白对虾(Penaeus vannamei)β-N-乙酰- D-氨基葡萄糖苷酶的抑制动力学

β-N-乙酰-D-氨基葡萄糖苷酶与南美白对虾的食物消化吸收、蜕壳生长有着密切关系. 海水里存在的有机污染物将影响酶生理功能, 从而进一步影响虾的正常蜕壳,严重将导致对虾的死亡. 醋酸酐是常用的有机溶剂, 故本文应用动力学方法研究醋酸酐对南美白对虾β-N-乙酰-D-氨基葡萄糖苷酶催化pNP-NAG水解时酶活力的变化规律. 表明在醋酸酐浓度低于20.0 mmol/L, 酶的抑制作用是可逆的, 测得醋酸酐对酶抑制的IC50为9.0 mmol/L. 用双倒数作图法测定醋酸酐与游离酶(E)和酶-底物络合物(ES)的结合平衡常数, 结果显示醋酸酐是酶的非竞争性抑制剂. 用底物反应动力学方法观测在不同底物浓度下酶在0.0、3.0、6.0、9.0、12.0 mmol/L的醋酸酐溶液中的失活过程,分别测定了酶的微观失活速度常数k+0及复活速度常数k-0, 结果表明醋酸酐对酶的影响是快速结合再缓慢失活的过程. 比较微观失活速度常数k+0及复活速度常数k-0, 结果暗示在高浓度的醋酸酐溶液中, 酶将完全失活.     

微生物嗜盐酶的研究进展

嗜盐酶一般来自于嗜盐菌,它的主要特点是严格依赖体系中一定的盐离子浓度,可以在高盐环境中维持其结构稳定,并且能够抵抗高温、p H和有机溶剂存在下的变性,因此在高盐、水/有机和非水介质环境的催化中具有重要的应用价值。本综述从盐对嗜盐酶活性和稳定性的影响、金属离子和有机溶剂对嗜盐酶的影响几个方面介绍了嗜盐酶的特点。在总结蛋白质数据库(PDB)中已有嗜盐酶的结构和特点的基础上,对嗜盐酶的嗜盐机制进行了分析,认为嗜盐酶不同于非嗜盐酶的特点在于盐桥和氢键明显增多,含有一些特殊的盐离子结合位点并且常以低聚体的形式存在,表面酸性氨基酸含量明显增多。最后对嗜盐酶的分子改造和应用进行了简要的介绍。     

半夏内生真菌所产β-葡萄糖苷酶的酶学特性研究

从半夏中分离筛选得到一株植物内生真菌,提取培养液中的β-葡萄糖苷酶,研究其酶学特性。结果表明:该菌种所产β-葡萄糖苷酶的最适反应温度在45~50℃之间,最适p H在7~8之间;在低于40℃条件下,p H为6~9时,酶活较稳定;其最适反应时间为40 min,金属离子和有机溶剂对酶活性影响都很大,在最适反应条件下其酶活为(77.83±0.42)U/m L。     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.