有机介质中脂肪酶催化外消旋苯甘氨酸甲酯的对映体选择性氨解反应

由水解酶催化的酯的对映体选择性水解和醇解反应 ,已在外消旋物质的拆分中得到广泛应用[1 ] 。近年来的一些研究表明 ,某些水解酶还可催化一些非天然酰基受体的转化 ,如过氧化氢、烷基胺、联胺和氨等。这些非天然酰基受体的转化反应在多肽的合成及手性化合物的拆分中显示出巨大的应用前景。其中 ,以氨为酰基受体的酶促氨解反应 ,是继酶促对映体选择性水解、酯化及转酯反应之后的另一制备光学纯化合物的新反应[2 ] 。目前国际上对这一新反应的研究尚属起步 ,国内未见有对该反应研究的报道。(Ｄ ,Ｌ) 苯甘氨酸是半合成 β 内酰胺类抗生素的重…     

有机介质中的固定化酶反应

近年来非水介质中的酶催化反应正获得越来越多的研究和应用。使用有机介质替代传统的水溶液作为酶反应的介质,通常是为了增加疏水性底物或产物的溶解度,或者是为了促使水解反应逆向进行,以便利用水解酶催化合成一些非常有用的化合物。有机介质包括合少量有机助溶剂的均相水溶液系统、水／有机溶剂双相系统,以及含微量水的有机溶剂均相系统等几种类型[1],具体使用时要根据生物催化剂的性质、反应物的溶解性和反应器的型式等特点细加选择。尽管在有机溶剂中可直接使用酶粉作催化剂[k],但是效果并不太好。一方面天然酶在有机溶剂中容易变…     

有机介质中酶催化活性和选择性的调控

有机溶剂中酶的结构与功能与在水中有很大的不同,通过调整控制策略可系统地改善酶针对目标反应的活性和选择性,重点阐述了溶剂对酶催化反应的活性和选择性的影响,介绍了酶催化选择性的热力学预测模型。,     

反应介质对脂肪酶稳定性的影响

脂肪酶Ｌｉｐｏｚｙｍｅ＾ＩＭ在有机溶剂中的热稳定性显著提高,在水溶液中,热处理温度高于５０℃后,其催化甘油三酯水解的活力迅速下降,温度升到６０℃时,水解活力仅残存１３．６％,温度高于７０℃该酶完全失活,而在有机溶剂正庚烷中,温度高达８５℃仍表现出较高的活性,反应介质的疏水性越强,酶抗超声辐射变性作用的能力越强,经同样的超声辐射处理后,正已烷中Ｌｉｐｏｚｙｍｅ＾ＩＭ的酯水解活力仅损失１１．８％,而在     

水在有机介质酶催化反应中的作用

本文针对有机介质酶催化反应中水的作用,结合最新研究进展作了综合评述,指出水在有机介质中对维持酶的活力构象起到“润滑剂”作用,水活度是衡量水作用的有效参数。分析了酶的水化程度,水化方式,有机溶剂及固定化载体对酶活力的影响及其作用机理,并对反应过程中水的控制问题进行了讨论。     

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。     

生物催化反应对映选择性控制

合成光学纯的化合物在化学及生物化学的研究和发展中正变得越来越重要,尤其在制药行业中目前手性药物近占全球药品总销售额的三分之一。本文以生物还原反应为例,介绍一些控制反应对映选择性的方法。     

Arthrobacter K1108乙内酰脲酶反应条件和立体选择性研究

研究了Arthrobacter K1108乙内酰脲酶的反应条件,结果表明,K1108乙内酰脲酶的最适反应温度为55℃,最适pH为7.0,Co^2 和Fe^2 对该酶有激活作用,而Ca^2 有严重抑制作用。K1108乙内酰脲酶的底物专一性较强,其最适底物为5－苄基乙内酰脲,5－苯基乙内酰脲和5－吲哚甲基乙内酰脲均不能作为其有效底物。对K1108乙内酰脲酶立体反应机制研究结果表明,其乙内酰脲水解酶不具立体选择性,决定产物立体构型的酶是N－氨甲酰氨基酸水解酶。     

低水有机介质中的酶催化

酶不仅能在水溶液里催化化学反应,而且能在有机介质中显示催化活性．其中低水溶剂体系对有机合成最为有利．文章就低水溶剂体系中影响酶催化的三要素（水、溶剂和载体）以及酶在该体系表现出来的一些特殊性质进行了讨论,并列举了低水溶剂体系中的酶催化在有机合成,化学分析,和高分子化学等方面的应用．     

Effects of additives on efficiency and specificity of ligase detection reaction

Ligase detection reaction (LDR) is adaptable to a wide variety of applications ranging from scientific research to clinical diagnosis, especially in the field of nucleotide polymorphism discrimination and analysis. Efficiency and specificity of LDR are the most two important characteristics that influence its application. To improve the specificity or efficiency of ligase, optimization of the design of LDR probes and the reaction of LDR were investigated previously by most researchers. But the effects of additives on LDR have not been reported. In this study, the effects of additives (DMSO, Tween-20, glycerol, formamide, and PEG-6000) on LDR efficiency and specificity were investigated. The results showed that all of these compounds, except for Tween-20, could improve the specificity of LDR. PEG-6000 was proved to be the best additive among the five tested with an optimal concentration of 5% at which the highest yield was obtained with a relatively improved specificity.     

Theoretical indicators of enzyme reaction specificity from conserved information in amino acid sidechains

Amino acid sequences for 11 acetohydroxy acid synthase (EC 4.1.3.18; AHS) polypeptides with experimentally established activity were chosen for computational comparisons to detect conserved local information associated with reaction specificity for each sequence. Windowed analysis by Pearson product moment cross-correlation of six amino acid sidechain properties revealed locally conserved segments common to all proteins with AHS activity. Seven information segments were detected in the same arrangement in sequences for the large subunit polypeptides of prokaryotes, and in the sequences for single polypeptides of eukaryotic AHS. The information segments were numbered 1-7 according to sequential position, and sequence features such as cofactor binding sites were defined for specific segments. Extension of the information segment analysis to seven other proteins of the pyruvate decarboxylase superfamily permitted use of the content and organization of information segments to recognize four classes of enzyme reaction specificity. Estimates of information entropy, based upon a state space defined by reaction specificity, directly reflected the known reaction complexity for all but one enzyme examined. Our data suggest that development of information-segment models for enzyme superfamilies may improve the accuracy of inferring protein activity from sequence.     

Substrate specificity of tuliposide-converting enzyme,a unique non-ester-hydrolyzing carboxylesterase in tulip: Effects of the alcohol moiety of substrate on the enzyme activity

6-Tuliposides A (PosA) and B (PosB) are glucose esters accumulated in tulip (Tulipa gesneriana) as major defensive secondary metabolites. Pos-converting enzymes (TgTCEs), which we discovered previously from tulip, catalyze the conversion reactions of PosA and PosB to antimicrobial tulipalins A (PaA) and B (PaB), respectively. The TgTCEs, belonging to the carboxylesterase family, specifically catalyze intramolecular transesterification, but not hydrolysis. In this report, we synthesized analogues of Pos with various alcohol moieties, and measured the TgTCE activity together with a determination of the kinetic parameters for these analogues with a view to probe the substrate recognition mechanism of the unique non-ester-hydrolyzing TgTCEs. It was found that d-glucose-like structure and number of the hydroxyl group in alcohol moiety are important for substrate recognition by TgTCEs. Among the analogues examined, 1,2-dideoxy analogues of PosA and PosB were found to be recognized by the TgTCEs more specifically than the authentic substrates by lowering K_m values. The present results will provide a basis for designing simple, stable synthetic substrate analogues for crystallographic analysis of TgTCEs.     

Effects of polar additives on the enzyme enantioselectivity of an esterification reaction in organic solvents

Summary The enantioselectivity ofcandida cylindracea lipase in esterification between ibuprofen and 1-butanol in organic solvents is influenced by adding a small amount of polar solvents. The results show that both the solvents and the amount added affected the reaction. Addition of 0.05% (v/v) N,N-dimethylformamide increase the ee value of the ester from 57.5% of no addition to that of 91%.