植物细胞的非选择性阳离子通道

就植物细胞质膜和内膜系统的非选择性阳离子通道类型、对不同离子的选择性和其生理功能的研究进展进行了评述。     

酶促聚合：绿色的高分子材料合成技术

以酶促聚合为代表的绿色高分子合成途径，以其反应条件温和、产物多分散性低、无金属催化剂残留、高度立体和区位选择性等优势，成为医用高分子材料合成领域中的研究热点。目前，氧化还原酶、水解酶、转移酶均成功应用于聚合反应，其中脂肪酶催化的缩聚反应及开环聚合反应研究最为广泛，同时，以可逆加成-断裂链转移聚合和原子转移自由基聚合为代表的酶促可逆失活自由基聚合得到了快速发展。针对酶促聚合中单体及合成产物结构与性能单一、应用范围有限等缺陷，基于酶促聚合与原子转移自由基聚合、开环易位聚合等反应的偶联，制备了多种不同结构与性能的聚合物材料，推动了上述材料在药物与基因递送领域中的应用。本文综述了脂肪酶催化聚合、酶促可逆失活自由基聚合、酶促化学偶联催化等方面的研究进展，并探讨了目前研究的局限性和未来研究方向。     

选择性剪接在植物逆境相关基因表达调控中的作用

文章介绍了选择性剪接在信号转导分子、转录因子、剪接因子和抗逆功能蛋白等4个层面对与植物逆境胁迫相关基因表达调控的影响,以及植物逆境诱导的选择性剪接机制的研究进展。     

lncRNA选择性剪接调控的研究进展

长链非编码RNA (lncRNA)选择性剪接是指剪除未成熟lncRNA中的内含子,并将外显子连接起来生成成熟lncRNA的过程.在各类疾病发生和发展过程中,异常的选择性剪接起着重要作用. lncRNA选择性剪接直接参与膀胱癌、结直肠癌、肝癌、神经母细胞瘤等多种肿瘤的发病机制,且与胚胎发育、软骨毛发发育、多系统萎缩症等紧密相关.在此,我们对lncRNA选择性剪接的起因、调控机制以及对疾病影响的研究进展进行综述.此外,本文还介绍了两个与lncRNA选择性剪接相关的数据库(SpliceMap和LNCediting).     

基因选择性剪接的生物信息学研究概况

基因选择性剪接现象是真核生物基本而又重要的调控机制。由于基因的选择性剪接在形成生物复杂性和多样性上具有极其重要的作用,同时选择性剪接与许多人类疾病也密切相关。因此,研究基因选择性剪接是一项十分重要的工作。生物信息学作为一门新兴的学科在研究基因选择性剪接上起关键的作用,尤其在研究基因表达调控机制、选择性剪接基因预测以及选择性剪接基因进化上。本文综述了这方面的最新研究进展,为更深入了解真核生物基因的表达调控机理提供依据。     

环氧化物水解酶产生菌的筛选及产酶条件研究

手性环氧化物至少含有一个手性碳,通过选择性开环和官能团转换,可以方便地合成许多有价值的手性化合物,在制药、农药、香料、精细化学品工业上有着极其重要的应用价值[1]。因此,手性环氧化物的合成一直是一个重要的研究课题。     

mRNA选择性剪切在植物发育中的作用

mRNA选择性剪切（altemativesplicing）是生物体基因转录调控的基本方式之一,随着新一代测序技术的广泛应用,越来越多的基因的选择性剪切现象被揭示。在植物发育的不同阶段及其应对外界逆境胁迫的过程中,许多基因发生了选择性剪切,产生植物各个发育阶段所需的特定蛋白质来完成不同的发育过程和形成不同应答因子以适应外界环境的变化。本文从种子发育、器官形态发育、开花时间、生物钟调控、环境胁迫等方面综述选择性剪切在植物发育中的研究进展。     

mRNA选择性剪接的分子机制

真核细胞mRNA前体经过剪接成为成熟的mRNA,而mRNA前体的选择性剪接极大地增加了蛋白质的多样性和基因表达的复杂程度,剪接位点的识别可以以跨越内含子的机制(内含子限定)或跨越外显子的机制(外显子限定)进行。选择性剪接有多种剪接形式：选择不同的剪接位点,选择不同的剪接末端,外显子的不同组合及内含子的剪接与否等。选择性剪接过程受到许多顺式元件和反式因子的调控,并与基本剪接过程紧密联系,剪接体中的一些剪接因子也参与了对选择性剪接的调控。选择性剪接也是1个伴随转录发生的过程,不同的启动子可调控产生不同的剪接产物。mRNA的选择性剪接机制多种多样,已发现RNA编辑和反式剪接也可参与选择性剪接过程。     

选择性雌激素受体调节剂在绝经后女性中的应用研究进展

雷洛昔芬和泰莫西芬是人工合成雌激素受体调节剂,具有与雌激素受体的高亲和力,并且拥有在不同的靶组织可分别表现为雌激素 激动剂和拮抗剂的特性,因此又被称为选择性雌激素受体调节剂,这类药物的出现为患绝经后综合征的女性病人提供了新的用药选择。着 重综述雷洛昔芬和泰莫西芬等具代表性的选择性雌激素受体调节剂在绝经后女性中的应用研究进展。     

选择性剪接在Toll样受体4信号转导通路中的作用

Toll样受体4(Toll-likereceptor4,TLR4)属于模式识别受体,可识别来自G-细菌细胞壁的脂多糖(lipopoly-saccharides,LPS),并通过MyD88依赖途径或MyD88非依赖途径进行信号转导,引发核因子-κB(NF-κB)和其他转录因子的表达,从而诱导细胞因子、化学趋化因子的产生,引起系统性炎症反应。选择性剪接是真核生物控制基因表达的一种重要机制,在TLR4通路中很多信号分子都存在着选择性剪接产生的异构体,且这些剪接异构体分子大都可负性调控TLR4信号转导通路。本文针对这方面的研究进展作一综述。     

Enzymatic synthesis of polythioester by the ring-opening polymerization of cyclic thioester

A high molecular weight aliphatic polythioester was prepared by lipase-catalyzed polymerization of hexane-1,6-dithiol and dimethyl sebacate using the technique of ring-opening polymerization of a cyclic thioester. The cyclic thioester monomer was first prepared using lipase from Candida antarctica in dilute solution. The monomer was then polymerized by the same lipase in bulk to produce a polythioester with an M(w) of about 120 000 g/mol, which was significantly higher than that of a polythioester obtained by direct polycondensation of the dithiol and diacid. The polymerization rate and thermal properties of the product were measured and compared with those of the corresponding polyester prepared by ring-opening polymerization of a cyclic ester.     

Lipase/esterase-catalyzed ring-opening polymerization: A green polyester synthesis technique

In the last decade, there has been increased interest in lipase/esterase-catalyzed ring-opening polymerization as an alternative to metal-based catalytic processes. This review focuses on three components in the reaction system, namely biocatalysts, reaction medium and monomers. Novel lipases or esterases are described with particular emphasis on, those derived from thermophiles, immobilized enzymes and recombinant whole-cell biocatalysts. Green solvents in enzymatic ring-opening polymerization, including water, ionic liquids, supercritical carbon dioxide and hydrofluorocarbon solvents, are also discussed. Enzymatic ring-opening polymerization is reviewed with regard to the variety of polymers obtainable, such as polyesters, polycarbonates, polyphosphates and polythioesters. Among these, enzymatic synthesis of polyesters has been most widely investigated, and is discussed for lactones with small to large ring sizes. Finally, the mechanism of enzymatic ring-opening polymerization is described, which is generally accepted as a monomer-activated mechanism. Overall, the review demonstrates that lipase/esterase-catalyzed synthesis of polymers via ring-opening polymerization provides an effective platform for conducting “green polymer chemistry”.     

Synthesis of biodegradable poly-epsilon-caprolactone microspheres by dispersion ring-opening polymerization in supercritical carbon dioxide

A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.     

Revisiting the Ring-opening Bulk Polymerization of ε -caprolactones using Commercial Lipases

The lipase-catalyzed ring-opening polymerization of ε-caprolactone ( ε-CL) and its derivatives was revisited using seven commercial enzymes. Lipases from Pseudomonas fluorescens (AK) and porcine pancreatic lipase (PPL) gave the best results, in both reaction conversion and degree of polymerization. Dependency on temperature and added concentration of enzyme was investigated, and there was a linear correlation between M n and the conversion ratio. The reaction proceeded rather slowly and the residual activity of these enzymes after prolonged incubation in ε-CL was studied. There was a negative correlation between the conversion ratio in the polymerization reaction and the tolerance of the enzymes for the solvent (monomer). Accordingly, a mechanism involving enzymatic ring-opening and non-enzymatic (but catalytic) polymerization was proposed.     

Synthesis of poly(L-lactide) and polyglycolide by ring-opening polymerization

This protocol describes the synthesis of poly(L-lactide) by ring-opening polymerization of L-lactide using tin(II) 2-ethylhexanoate catalyst as well as the synthesis of polyglycolide by ring-opening polymerization of glycolide. Ring-opening polymerization of cyclic diesters synthesized from alpha-hydroxycarboxylic acids gives high-molecular-weight polyester in high yield. Tin(II) 2-ethylhexanoate catalyst is the most common catalyst for ring-opening polymerization of diesters owing to its high reactivity and low toxicity. Purity of monomers and the amount of water and alcohol in the reaction system are significant factors for increasing molecular weight and conversion of polyesters. The molecular weight of the polyesters is also dependent on reaction temperature and reaction time. This protocol can be completed in 3 d for the synthesis of poly(L-lactide) and 2 d for the synthesis of polyglycolide.     

Revisiting the Ring-opening Bulk Polymerization of ϵ -caprolactones using Commercial Lipases

The lipase-catalyzed ring-opening polymerization of &#107 -caprolactone ( &#107 -CL) and its derivatives was revisited using seven commercial enzymes. Lipases from Pseudomonas fluorescens (AK) and porcine pancreatic lipase (PPL) gave the best results, in both reaction conversion and degree of polymerization. Dependency on temperature and added concentration of enzyme was investigated, and there was a linear correlation between M n and the conversion ratio. The reaction proceeded rather slowly and the residual activity of these enzymes after prolonged incubation in &#107 -CL was studied. There was a negative correlation between the conversion ratio in the polymerization reaction and the tolerance of the enzymes for the solvent (monomer). Accordingly, a mechanism involving enzymatic ring-opening and non-enzymatic (but catalytic) polymerization was proposed.     

Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity

New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content. The receding contact angle varied from 27 to 44 degrees. The tensile properties of the copolymers were controlled by altering the PDXO block length. The tensile testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximately 600-800% and sigma(b) approximately 8-20 MPa) throughout the in vitro degradation study (59 days).     

In situ copolyesters containing poly(L-lactide) and poly(hydroxyalkanoate) units

In situ copolyesters containing polylactide (PLA) and polyhydroxyalkanoate (PHA) segments were obtained via ring-opening polymerization of L-lactide using PHA as a macroinitiator with stannous octoate as catalyst. Incorporation of PHA (20 wt %) into PLA affords a novel copolymer with Mn values ranging from 25 to 50 KDa and low polydispersities of 1.8-2.3. DSC analysis of the copolymer indicates well-defined crystallization and melting transitions different from the homopolymers and corresponding blend. The polymers were characterized by FT-IR, GPC, DSC, optical microscopy, NMR, and TGA. The results show successful reactivity of PHA as a macroinitiator for the ring-opening polymerization of lactide.     

Synthesis of 2,3,4,5-tetra-O-methyl-D-glucono-1,6-lactone as a monomer for the preparation of copolyesters

2,3,4,5-tetra-O-methyl-D-glucono-1,6-lactone has been prepared as a crystalline compound in acceptable yield by two different routes. An initial assay of copolymerization with L-lactide by ring-opening polymerization was carried out. The incorporation of the carbohydrate monomer into the polymer chain was about 2%.