乙酰木聚糖酯酶研究进展

半纤维素是一类丰富可再生而又亟待开发利用的生物质资源,将半纤维素降解为糖类进而生产木糖醇及其它化学品是利用生物质资源的关键一步。乙酰木聚糖酯酶是降解半纤维素的一个重要酶,它能够水解乙酰化木聚糖中的木糖残基上的2位和3位的O 乙酰基,在工业、农业及食品业具有广阔的应用前景。综述了乙酰木聚糖酯酶的分类、酶学性质、催化机制、基因克隆和协同酶解等方面的研究进展,同时对该研究进行了展望。     

对家鸡血清酯酶发育调控的初步研究

采用垂直平板聚丙烯酰胺凝胶电泳方法跟踪测定了 １０ 羽优黄 ３８０ 商品蛋鸡血清酯酶的遗传表现型,结果表明：血清酯酶（ Ｅｓ１）的遗传表达具有明显的发育阶段差异性,开产前均为有带类型,并表现出遗传多态现象,开产后 Ｅｓ１ 酶带消失,表现为无活性 Ｏ 型⒚对 Ｉ Ｓ Ａ Ｂ３８０ 父母代 Ｃ Ｄ 母鸡的扩大抽样测定结果验证了上述的结论⒚由此我们推测,母鸡产蛋期 Ｅｓ１ 区无活性“ Ｏ 型”可能是基因表达在不同发育阶段调控（抑制）的结果,因此不存在“ Ｅｓ１基因座位上决定 Ｏ 型的等位基因 Ｅｓ１ｏ ⒚ Ｅｓ１ 基因在开产前处于转录活跃状态,开产后基因转录就被抑制,以维持产蛋期母鸡体内所需较高的血脂水平⒚母鸡血清酯酶表达发育遗传学规律可能广泛存在于家禽各种群体之中⒚如果该推测成立的话,家鸡酯酶的生物合成就可能成为研究禽类基因表达和调控的理想模型⒚     

胡萝卜愈伤组织细胞中两个重力相关酯酶的特性

在从胡萝卜愈伤组织细胞中分离出两个与重力作用相关的酯酶（ｇｒＥＳＴ１ 和ｇｒＥＳＴ２）后（ 蔡伟明等１９９８） ,对这两个酯酶的性质作了进一步研究。发现它们具有非常独特的抗ＳＤＳ的特性。脱氧胆酸盐对它们的活力有部分的抑制作用。β苯丙酸、ＡｇＮＯ３ 和ＣｕＳＯ４ 对它们的活力没有抑制作用。抗坏血酸和半胱氨酸对它们的活力有抑制,特别是半胱氨酸有明显的影响。分别加去污剂脱氧胆酸盐、Ｔｒｉｔｏｎ Ｘ１００ 和ＳＤＳ的非变性电泳测得ｇｒＥＳＴ１ 和ｇｒＥＳＴ２ 的分子量分别在４９ ～６６ ｋＤ 和４３ ～５９ ｋＤ 范围附近。它们的等电点分别约为ｐＨ５ ．４ 和４ ．９ 。它们可以在４０ ％ 硫酸铵饱和度时沉淀,并可以用这个方法将它们部分纯化     

STABILITY OF ORGANOPHOSPHATE RESISTANCE IN CULEX PIPIENS PALLENS COQUILLETT UNDER RELAXATION OF INSECITICDE SELECTION*

Abstract The stability of resistance in the organophosphate resistant strain of Culex pipiens pallens with amplification of single gene coding for esterase B₂ was determined under relaxation of insecticide selection. Insecticide resistance and amplification of esterase were both lost when strains were not homozygous for the presence of amplified gene, probably due to biological disadvantage of the esterase gene. LC₅₀ and LC₉₅ of chlorpyrifos for this strain were 0. 2099 mg/L and 0.9036 mg/L in the F₀ generation respectively, but 0. 0207 mg/L and 2. 8027 mg/L respectively in the F₁₆ generation. In the homozygous strain, insecticide resistance was still stable and amplification of esterase remained after 16 generations under relaxation of insecticide selection, which indicated that copy of esterase gene was not lost in the offspring of this strain. The evolution of insecticide resistance in mosquitoes is discussed.     

Inhibition of neuropathy target esterase expressing by antisense RNA does not affect neural differentiation in human neuroblastoma (SK-N-SH) cell line

Neuropathy target esterase (NTE) is phosphorylated and aged by oraganophosphorus compounds (OP) that induce delayed neuropathy in human and some animals. NTE has been proposed to play a role in neurite outgrowth and process elongation during neural differentiation. However, to date, there is no direct evidence of the relevance of NTE in neural differentiation under physiological conditions. In this study we have investigated a possible role for NTE in the all-trans retinoic acid (ATRA)-induced differentiation of neuroblastoma cells by antisense RNA. A NTE antisense RNA construct was generated and then transfected into human neuroblastoma SK-N-SH cells. A positive cell clone that can stably express NTE antisense RNA was obtained by G418 selection and then identified by western blotting. NTE activity was depressed in the transfected cells with only about 50% activity of the enzyme in the control cells. ATRA-induced differentiation of the neuroblastoma cells with lowered NTE activity revealed that inhibition of NTE expression does not affect neural differentiation in SK-N-SH cells. The result suggested that organophosphates may inhibit neural differentiation by initially acting on other targets other than NTE.     

Production of lipolyzed butteroil by a calf pregastric esterase immobilized in a hollow fiber reactor: III. Effect of glycerol

Lipolysis of butter oil in a hollow fiber reactor containing an immobilized calf pregastric esterase was studied at 40 degrees C, a pH of 6.0, and glycerol concentrations of 0, 150, and 500 g/L in the buffer solution. The concentrations of 10 fatty acid species in the lipolyzed product were determined using high-performance liquid chromatography. The rate of loss of enzyme activity and the relative selectivities of this esterase depended on the glycerol concentration. By contrast, the overall rate of release of fatty acids was not affected by the glycerol concentration. Loss of enzyme activity was modeled using first-order kinetics. The models for deactivation and reaction kinetics were fit simultaneously to the data. The model was successful in describing the rates of release of all 10 fatty acid species for a range of space times from 0 to 25 h. The parameters of the model were tested for dependence on glycerol concentration.     

Anatomical and Histochemical Changes of Norway Spruce Buds Induced by Simulated Acid Rain

The study was focused on changes of anatomical and histochemical parameters of buds of 4-year-old Norway spruce (Picea abies L. Karst) trees subjected to simulated acid rain (SAR). Solutions of pH 2.9 and 3.9 were applied by spraying on shoot and/or by watering for two years. No macroscopic changes of buds or needles were observed in connection with SAR application and the only induced change was 2-week earlier onset of bud break in all treated variants compared to the control. Two-year treatment caused decrease in number of leaf primordia and increase in number of living bud scales in treated dormant buds while these parameters remained unchanged in the control buds. Treatments with solution of pH 2.9 caused decrease of flatness of bud apical meristem during the vegetative season. Increased activity of non-specific esterase in treated buds occurred during dormancy and bud break and the enhanced accumulation of phenolic compounds was detected at the beginning of shoot growth. Changes in histochemical parameters of bud tissues were induced mainly by spraying of shoots and can thus be qualified as primary damage.     

Methods to increase enantioselectivity of lipases and esterases

Lipases and esterases are frequently used in the synthesis of optically pure compounds; however, natural enzymes do not always show sufficiently high enantioselectivity. Variation of the structure of the substrates, modification of the reaction system or protein engineering (e.g. the expression of pure enzymes, rational design or directed evolution) are strategies that can be employed to improve the distinction between two enantiomers or enantiotopic groups.     

Carbohydrate esterase family 4 enzymes: substrate specificity

The substrate specificity of selected enzymes classified under Carbohydrate Esterase family 4 (CE4) has been examined. Chitin deacetylase from Mucor rouxii and both a native and a truncated form of acetyl xylan esterase from Streptomyces lividans were found to be active on both xylan and several soluble chitinous substrates. Furthermore, the activities of all enzymes examined were significantly increased in the presence of Co(2+) when chitinous substrates were employed. However, the presence of this metal ion did not result in enhancing the activities of the enzymes when xylan was used as substrate. An acetyl xylan esterase from Bacillus pumilus, classified under Carbohydrate Esterase family 7, was found to be inactive towards all chitinous substrates tested. Finally, all enzymes examined were inactive towards cell wall peptidoglycan.     

Thermostable esterase from Thermoanaerobacter tengcongensis: high-level expression, purification and characterization

The lipA gene encoding a thermostable esterase was cloned from Thermoanaerobacter tengcongensis and overexpressed in Escherichia coli. The recombinant esterase, with a molecular mass of approx. 43 kDa determined by SDS-PAGE, was purified to homogeneity through Sephadex G-100 gel filtration. The purified enzyme actively hydrolyzed tributyrin but not olive oil. Maximum activity was observed on p-nitrophenyl (NP)-propionate (C3) and p-NP-butyrate (C4), with little activity towards p-NP-palmitate (C16). The esterase was optimally active at 70 °C (over 15 min) and at pH 9. It is highly thermostable, with a residual activity greater than 80% after incubation at 50 °C for more than 10 h. The activity was not inhibited by 5 mM EDTA and PMSF, indicating the esterase is not a metalloenzyme and may contain a specific structure around the catalytic serine residue. In addition, it was stable for 1 h at 37 °C in 1% CHAPS and Triton X-100 but not stable in 1% Tween 20 or SDS.