Phosphorothioate Analogues of Nucleotides—Tools for the Investigation of Biochemical Processes

Nucleoside phosphorothioates are analogues of nucleotides with a wide range of applications. Thus, on the one hand, in many but not all cases they are more stable against hydrolysis than the unmodified nucleotides—a property which they share with other nucleotide analogues. On the other hand, however, they are good substrates for many, but not all reactions where the nucleotide or the phosphorothioate group is transferred to an acceptor other than H₂O. As a consequence, once incorporated into a system such as DNA, phosphorothioates cannot be easily removed. What makes these compounds unique to a certain extent is the chirality at the phosphorus center if two nonequivalent residues are linked to the phosphorothioate group. This opens the way for the use of these compounds to investigate stereochemical aspects of enzymatic reactions. In addition to these properties, there are those expected from exchange of an oxygen for a sulfur atom in a phosphate group, e.g. the increased affinity towards mercury derivatives and the large chemical shift of the ³¹P-NMR sinals. If one considers how many biologically interesting compounds contain phosphate groups, the considerable interest in these nucleotide analogues is not surprising.     

Dynamic Phosphorus: Thiolate Exchange Cascades with Higher Phosphorothioates

In this study, we introduce phosphorus, a pnictogen, as an exchange center for dynamic covalent chemistry. Cascade exchange of neutral phosphorotri- and -tetrathioates with thiolates is demonstrated in organic solvents, aqueous micellar systems, and in living cells. Exchange rates increase with the pH value, electrophilicity of the exchange center, and nucleophilicity of the exchangers. Molecular walking of the dynamic phosphorus center along Hammett gradients is simulated by the sequential addition of thiolate exchangers. Compared to phosphorotrithioates, tetrathioates are better electrophiles with higher exchange rates. Dynamic phosphorotri- and -tetrathioates are non-toxic to HeLa Kyoto cells and participate in the dynamic networks that account for thiol-mediated uptake into living cells.     

Coupling of a Nucleoside with DNA by a Methyltransferase

How to outwit a methyltransferase: Methyltransferases (Mtases) catalyze the transfer of the activated methyl group from the cofactor S-adenosyl-L -methionine ( 1 ) to acceptors R within a large variety of biomolecules. Through the use of the cofactor analogue 2 a whole nucleoside was coupled to DNA in a Mtase-catalyzed reaction.     

利用壳聚糖的絮凝性质包埋酶的葡萄糖氧化酶电极

本文利用壳聚糖的絮凝性质，将葡萄糖氧化酶包埋在壳聚糖与多聚磷酸盐的絮絮沉淀中，操作简单，固定化效率高。研究了适合了酶电极使用的最佳固定化条件。     

Studies on Enzyme Kinetics by Microchip and Related Techniques

Both conventional and microchip-based capillary electrophoresis(CE) technologies have been used for the analysis of enzymes. Practical procedures of using CE to determine the Km and Vmax values of an enzyme have been developed. By studying the inhibition to the enzyme, it is possible to select a suitable drug candidate. When compared with the conventional CE method, single lane microchip-based method can improve the speed for the assay three times. By using multiple lane-based microchip, the speed can be further increased.     

Kalman滤波用于酶反应动力学的研究

采用卡尔曼滤波研究酶反应动力学及分析，依据酶存在下过氧化氢放出氧的反应建立了扩展Ｋａｌｍａｎ滤波模型，用滤波处理确定了反应速率与起始速率浓度的关系，并估算出酶反应动力学参数Ｋｍ。     

Enzyme mimics

Chemists are trying to create synthetic molecules which mimic the recognition and catalytic properties of real enzymes. One target of interest is catalysis of reactions for which there are no known natural enzymes. Inspired by the examples of nature, approaches to the design of enzyme mimics for catalysis of Diels-Alder reaction are described. The design is based on porphyrin molecular boxes and zinc co-ordination. The potential of design of enzyme mimics employing cholic acid and other systems is also discussed.     

不同形貌PbS 纳米粒子形成机理的探讨

采用聚乙二醇辛基苯基醚(OP)/正戊醇/环己烷/水溶液所形成的W/O型微乳液中的水核作软模板,合成了不同形貌如球形、立方体形、纺锤形、梭形和棒形的PbS纳米粒子。运用透射电子显微镜(TEM)对产物的形貌进行了表征。考察了W/O型微乳液中水与表面活性剂的物质的量的比(ω0)、反应物浓度和陈化时间等条件对产物形貌的影响。对不同形貌PbS纳米粒子的形成机理进行了探讨。     

Determination of Serum Urea with an Enzyme Thermistor Using Immobilized Urease

Abstract

The application of an enzyme thermistor device in a simple and accurate procedure for the determination of serum urea is described. The enzyme thermistor measures the heat produced when urea is passed through a small column containing immobilized urease. The stability and sensitivity as well as the performance with clinical serum samples of the system is evaluated. Advantages are the simplicity, the low enzyme cost and the insensitivity to the optical properties of the sample and interfering substances, which may affect the commonly used assay procedures.     

Triesterase and Promiscuous Diesterase Activities of a Di‐CoII‐Containing Organophosphate Degrading Enzyme Reaction Mechanisms

The reaction mechanism for the hydrolysis of trimethyl phosphate and of the obtained phosphodiester by the di‐Co^II derivative of organophosphate degrading enzyme from Agrobacterium radiobacter P230(OpdA), have been investigated at density functional level of theory in the framework of the cluster model approach. Both mechanisms proceed by a multistep sequence and each catalytic cycle begins with the nucleophilic attack by a metal‐bound hydroxide on the phosphorus atom of the substrate, leading to the cleavage of the phosphate‐ester bond. Four exchange‐correlation functionals were used to derive the potential energy profiles in protein environments. Although the enzyme is confirmed to work better as triesterase, as revealed by the barrier heights in the rate‐limiting steps of the catalytic processes, its promiscuous ability to hydrolyze also the product of the reaction has been confirmed. The important role played by water molecules and some residues in the outer coordination sphere has been elucidated, while the binuclear Co^II center accomplishes both structural and catalytic functions. To correctly describe the electronic configuration of the d shell of the metal ions, high‐ and low‐spin arrangement jointly with the occurrence of antiferromagnetic coupling, have been herein considered.     

Enzyme assays with boronic acid appended bipyridinium salts

In-vitro fluorescent enzyme assays have been developed for sucrose phosphorylase (SPO) and phosphoglucomutase (PGM). These assays make use of a selective carbohydrate sensing system that detects the unlabeled enzymatic products fructose and glucose-6-phosphate. The system comprises 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt as the reporter unit and boronic acid appended viologens as selective receptors with working ranges from 70 μM to 1.0 mM for fructose (SPO) and 190 μM to 2.0 mM for glucose-6-phosphate (PGM). The change in fluorescence can be converted into product concentration, allowing initial reaction velocities and Michaelis-Menten kinetics to be calculated. The assays are also carried out in multiwell plate formats, making them suitable for high-throughput screening of enzyme inhibitors. Rapid PGM inhibition screening is demonstrated with EDTA and LiCl. The PGM assay can also be used for enzyme quantification with a detection limit of 50 ng mL⁻¹.     

Recent Advances in Electrochemical Enzyme Immunoassays

Enzyme immunoassays (EIAs) are currently the predominant analytical technique for the quantitative determination of a broad variety of analytes in clinical, medical, biotechnological, and environmental significance. Although the most common detection methods for EIAs are based on spectroscopic measurements, electrochemical techniques, due to their high sensitivity, selectivity, simplicity and low cost, have emerged as a very attractive alternative to carry out the detection step in this kind of assays. The intention of this review is to cover the progress and development in integrating electrochemical detection methods with EIAs, over the past five years.     

Effect Of Temperature on the Sensitivity of Sandwich Enzyme Immunoassay with Fab'-Horseradish Peroxidase Conjugate

Abstract

Effect of temperature was examined on the sensitivity of sandwich enzyme immunoassay for human chorionic gonadotropin (hCC) with anti-hCG Fab'-horseradish peroxidase conjugates prepared by using three different reagents (N-succinimidyl 4-(N-maleimidomethyl) cyclohexane-l-carboxylate, glutaraldehyde and metaperiodate). The non-specific bindings of the conjugates to anti-hCC IgG-coated polystyrene balls were much lower at 20°C than at 37°C, and the specific bindings were slightly higher at 20°C than at 37°C. The lowest non-specific binding and the highest specific binding were obtained by incubation at 20°C with the maleimide conjugate. As a result, the sensitivity could be more easily improved by incubation at 20°C than at 37°C and the highest sensitivity was obtained with the maleimide conjugate. Similar results were also obtained for other macromolecular antigens such as human ferritin and α-fetoprotein.     

酶催化脂肪族聚酯的合成

脂肪族聚酯是一种可生物降解的新型高聚物,可通过化学催化、发酵和酶催化来合成.酶催化合成聚酯是一种新型的环境友好绿色化学技术,可以在温和条件下高效的合成聚酯,有着传统聚合方法难以比拟的优势.尤其是特种酶的应用,为传统方法难以合成的聚酯,开辟了一条新的合成途径.本文综述了脂肪酶催化缩聚、酯交换、内酯开环聚合等聚酯合成方法,并讨论了反应参数(如溶剂、温度、酶和单体的浓度)对反应的影响.     

New Tripodal, “Supercharged” Analogues of Adenosine Nucleotides: Inhibitors for the Fhit Ap3A Hydrolase

Methanetrisphosphonic acids provide a branch point for synthetic nucleotide analogues which can be exploited either to generate novel tripodal nucleotides or to incorporate additional negative charge into linear analogues relative to the parent nucleotide, as exemplified in the picture for ATP and diadenosine tetraphosphate (Ap₄A). These compounds show valuable discriminatory behavior as competitive inhibitors for the tumor suppressor protein Fhit and a second Ap_nA pyrophosphohydrolase. X=H, Cl, F.     

偶合反应伏安酶联免疫分析测定人血清乙型肝炎E抗体的研究

本文提出用竞争性抑制偶合反应伏安酶联免疫分析法测定人血清乙型肝炎Ｅ抗体（ＨＢｅＡｂ）方法基于酶标ＨＢｅＡｂ辣根过氧化物酶（ＨＲＰ）催化Ｈ２Ｏ２氧化邻联甲苯胺（ＯＴ）的反应与邻联甲苯胺氧化产物在电极上的还原反应相偶合，测定标记在ＨＢｅＡｂ上ＨＲＰ量，以求得抑制免疫反应的乙型肝炎Ｅ抗体含量本法测定酶标ＨＢｅＡｂＨＲＰ及ＨＢｅＡｂ的灵敏度均高于经典的ＥＬＩＳＡ光度法方法用于病人血清样品分析，与ＥＬＩＳＡ光度法对照，其相关性很好     

生物催化剂酶在高分子改性中的应用

生物催化剂酶用于高分子合成及改性的研究正在成为国外学者的一个新的研究热点，酶催化反应的专一性，高效性，高选择性及反应条件的相对温和性，使酶催化反应在高分子改性领域更具吸引力，为高分子改性开辟了一条更为清洁，更高效的途径。本文综述了近年来酶催化反应在高分子改性方面的研究进展。     

利用60%季铵化聚(4-乙烯)吡啶固定化酶的电位型尿素酶电极的研制

在电位型尿素酶电极的组装过程中，要求尽量不改变尿素酶的构型和构象，使其在酶膜中保持其自然状态，从而可获得较高的酶活力．用ｐＨ玻璃电极作原电极，将尿素酶固定在其表面，常用的有戊二醛交联法［１］和各种聚合物膜法［２～４］．本文利用６０％季铵化的聚（４－乙...