分子动力学模拟尿素对水溶液中蛋白质构象转变的影响

采用分子动力学方法和全原子模型研究尿素和水分子对模型蛋白S-肽链结构转化的影响。模拟结果显示S-肽链的变性速率常数k值随着尿素浓度的增加而先降低后升高,在尿素浓度为2.9 mol/L时达到最低值。模拟了不同尿素浓度下尿素-肽链、水-肽链以及肽链分子氢键的形成状况。结果表明:尿素浓度较低时,尿素分子与S-肽链的极性氨基酸侧链形成氢键,但不破坏其分子内的骨架氢键,尿素在S-肽链水化层外形成限制性空间,增强了S-肽链的稳定性。随着尿素的升高,尿素分子进入S-肽链内部并与其内部氨基酸残基形成氢键,导致S-肽链的骨架氢键丧失,S-肽链发生去折叠。上述模拟结果与文献报道的实验结果一致,从分子水平上揭示了尿素对蛋白质分子结构变化的影响机制,对于研究和发展蛋白质折叠及稳定化技术具有指导意义。     

尿素对钼铁蛋白的活性和金属原子簇稳定性的影响

当尿素浓度高于０．５ ｍ ｏＬ／Ｌ时,棕色固氮菌（Ａｚｏｔｏｂａｃｔｅｒｖｉｎｅｌａｎｄｉｉ）固氮酶钼铁蛋白的乙炔还原活性呈指数下降;而经厌氧缓冲系统稀释并保温后,又可得到明显恢复。尿素对邻菲口罗啉从还原的或部分缺失Ｐ－ｃｌｕｓｔｅｒ 的ＭｏＦｅ 蛋白中螯合金属原子簇的Ｆｅ 原子均有较大的促进作用。还原ＭｏＦｅ 蛋白在尿素梯度凝胶电泳中的迁移率：在０～１．５ ｍ ｏｌ／Ｌ内,无明显变化;在１．５～５．０ ｍ ｏｌ／Ｌ内,线性变小;在５．０～８．０ ｍ ｏｌ／Ｌ内,则呈平缓状态。结果表明：（１）尿素对不同状态的ＭｏＦｅ 蛋白金属原子簇的影响程度不尽相同,而对蛋白质的变构作用是尿素影响ＭｏＦｅ 蛋白的活性和金属原子簇稳定性的主要原因;（２）ＭｏＦｅ 蛋白的构象与金属原子簇密切相关;（３）ＭｏＦｅ 蛋白在变性过程中,活性下降可能先于分子整体构象的变化     

氢离子敏场效应管型尿素传感器及其应用

在H+-IS FET(离子敏场效应晶体管)的二个栅极表面分别复盖一层成二醛交联的牛血清清蛋白－脲酶膜及牛血清清蛋白膜即制成差分式尿素－酶FET传感器。该传感器的响应时间小于1min。尿素浓度为1．O－8．0mg／dL时,响应值与尿素浓度对数值里线性关系,线性相关系数为0．997,响应灵敏度为50mV／dec．(mg／dL)。尿素浓度为0．1—1．Omg／dL时,响应值与尿素浓度呈线性关系,线性相关系数为O．998,响应灵敏度为12—15mV／mg／dL。该传感器对l00mg／dL尿素溶液的20次响应的标准偏差及变异系数分别为1．39mv和1．44％。用该尿素一酶FET测定血清样品中的-BUN(血中尿素氮)值时,与酶法相比较,两者之间的相关系数为o．9912。该传感器在1个半月内累计使用250次后,响应灵敏度下降约10％。     

间歇腹膜透析的数学模型

在80年代,腹膜透析(PD)治疗急慢性肾功衰有了很大发展。为了探索透析治疗过程中溶质浓度的动力学变化,实现有效透析,建立数学模型是必要的。近十余年国外对此作过一些研究,但均限于一次透析的单室单指标模型,Farrel甚至认为“PD”的模型“还未被公开探讨”。国内尚未见过这方面的报导。本文采用三室模型,以尿素氮(BUN)、肌酐(Cr)为指标,对间歇腹膜透析(IPD)全过程,建立了动力学模型(BCKM)。它能够在PD治疗中,预测与监测透析的全过程。并给出长期透析的最佳处方。     

尿素对小鼠体表心电图和心室肌细胞钠离子通道电流的影响

目的：观察尿素对小鼠体表心电图和心室肌细胞钠离子通道电流的影响。方法：使用常规的心电图记录方法和膜片钳实验技术,分别记录小鼠体表心电图和心室肌细胞钠离子通道电流。结果：尿素可以使小鼠心率明显减慢（P〈0．01）,呈浓度依赖性,低、中、高三个剂量组的心率分别由给药前的（612±27、615±23、619±26）b·min^-1下降到给药后的（556±29、469±37、378±48）b·min^-1,并且中、高剂量组发生了不同程度的传导阻滞性心律失常;尿素对小鼠心室肌细胞钠电流有明显的抑制作用（P〈0．05）,钠电流分别由给药前的（8．76±0．91、8．87±1．01、8．77±0．96）nA降低到给药后的（7．32±0．68、5．69±0．64、4．58±0．57）nA,呈浓度依赖性。结论：尿素可以通过抑制心室肌细胞钠电流使小鼠发生传导阻滞性心律失常。     

尿素施用量对小麦根际土壤微生物数量及土壤酶活性的影响

在大田高产条件下,研究了不同尿素施用量下两种不同穗型小麦品种“兰考矮早8”和“豫麦49—198”根际微生物数量和土壤酶活性的变化。结果表明：微生物数量随小麦生育时期的进行呈规律性变化,其中微生物总量在拔节期和抽穗期时数量较多。尿素施用量对小麦根际微生物数量和酶活性均产生一定的影响,并且处理间差异达到显著水平。两个小麦品种根际微生物总量、细菌、放线菌、真菌数量随着尿素施用量的增加呈先上升后下降的趋势,但两个品种根际微生物数量最高时的尿素量略有差异。同一生育时期,随着尿素施用量的提高,土壤蛋白酶、过氧化氢酶呈先增加后降低的变化趋势,以他（391kg／hm^2）或T3（586kg／hm^2）处理的酶活性较高,T4（782kg／hm^2）处理的酶活性略有降低;脲酶活性则呈上升趋势,以T4（782kg／hm^2）处理的脲酶活性最大。表明适宜尿素施用量有益于小麦根际微生物数量和酶活性的提高,过高则微生物数量和酶活性下降。     

壳聚糖金属离子配合物吸附尿素性能研究

由于尿素吸附剂存在吸附容量低、吸附选择性差、生物相容性和血液相容性差等缺点,使人工肾和口服尿素吸附剂的应用受到限制．近几年,尿素吸附材料方面的研究进展较快,主要有：１９９０年,藤田良枝用活性炭作尿素吸附剂,吸附量为９０ｍｇ／ｇ（尿素初始浓度为２１００ｍｇ／Ｌ）,吸附容量低,且微炭粒易脱落,有造成栓塞的危险,不宜作人工肾材料［１］;１９９３年,何炳林等用交联聚丙烯酸固载化氧化β环糊精作尿素吸附材料,吸附容量较高,为８２１ｍｇ／ｇ（尿素的初始浓度为１３００ｍｇ／Ｌ）．由于其利用的是Ｓｃｈｉｆｆ…     

包膜尿素在华北平原夏玉米上的应用

通过连续2a的大田试验,比较研究了尿素与包膜尿素对夏播玉米郑单958和农大108产量、水分利用效率（WUE）、氮肥利用率（NUE）与土壤无机氮动态的影响,结果表明：产量与WUE随施氮量增大而增大,两种氮肥间差异不显著;包膜尿素NUE较尿素高,2004年郑单958N90kg／hm^2与农大108N180ks／hm^2条件下提高显著;施氮对土壤无机氮动态的影响具有年际间差异：2004年不施氮条件下一般呈“V”型变化趋势,施氮使其向“N”型或倒“V”型转变,而2005年施氮与不施氮条件下均呈“N”型变化趋势;施氮使土壤无机氮含量明显提高,包膜尿素较尿素效果更明显;土壤无机氮含量,包膜尿素处理以表土层最高,而尿素处理,特别是尿素N180kg／hm^2处理9叶展至吐丝期以下层土壤较高,2004年表现尤为明显。可见在降水量较多的年份,包膜尿素缓释效应明显,能有效控制无机氮的下移。华北平原夏玉米季以包膜尿素替代尿素、以一次性基施替代基肥＋追肥是完全可行的,能达到省工、增效、环保目的。     

控释尿素和普通尿素配比对不同氮效率玉米叶片衰老特性和土壤酶活性的影响

控释尿素和普通尿素配比施用可以同步玉米氮素需求,延缓后期衰老,增加产量。本试验以黄淮海区域两种氮效率玉米作为对象,研究控释尿素和普通尿素不同配比对其叶片衰老特性、土壤酶活性和土壤无机氮的影响。试验选取黄淮海主栽玉米品种豫禾988（氮低效）和郑单958（氮高效）作为试验材料,设置6个施氮处理（CK、N180U、N180C1、N180C2、N180C、N300U）,其中CK为不施氮处理,180、300代表施氮水平分别为180 kg/hm²和300 kg/hm²,U代表全尿素处理（基肥：追肥=2：3）,C1、C2分别代表控释氮：尿素氮为1：2和2：1（基肥一次施用）,C代表全控释尿素处理（基肥一次施用）。2018-2019年结果表明：与CK相比,豫禾988在N180C1和郑单958在N180C2处理下,能够在玉米生育后期显著提高穗位叶超氧化物歧化酶（SOD）和过氧化物酶（POD）活性,降低膜脂过氧化物（MDA）含量,同时也增加了土壤无机氮含量、脲酶和蔗糖酶活性。综上所述,针对不同氮效率玉米品种,通过控释尿素和尿素合理配施,利用速效氮和控释氮的释放来延缓玉米功能叶片衰老,延长功能期,提高生育后期土壤无机氮含量和酶活性,共同促进玉米生长,增加玉米产量,其中豫禾988和郑单958分别在N180C1和N180C2处理下效果最佳。     

新型缓释尿素对拟南芥生长和遗传毒性的影响研究

新型缓释尿素的成功研制对提高肥料利用率、降低环境污染有重要意义.用模式植物拟南芥作为研究对象,普通尿素作为对照,通过拟南芥主根长、鲜重、须根数研究新型缓释尿素对拟南芥生长的影响.用控释剂对拟南芥施用,通过拟南芥同源重组频率研究控释剂对拟南芥遗传毒性的影响.结果表明,缓释尿素及普通尿素随着浓度增加对拟南芥的生长都有先促进后抑制的趋势,低浓度施用条件下缓释尿素对拟南芥的生长促进作用更加明显,高浓度施用条件下普通尿素对拟南芥的抑制作用更加明显.尿素浓度达到1000 μg/mL时,拟南芥可以正常萌发,但是不能存活.控释剂施用对拟南芥遗传毒性分析表明,控释剂不影响拟南芥同源重组频率,表明在本实验浓度范围内控释剂暴露对拟南芥未产生遗传毒性影响.研究结果为该新型缓释尿素在生产上应用推广打下基础.     

A Multistage Well‐Mixed Model for Urea Removal from Industrial Wastewater

A multistage well‐mixed model for urea removal from industrial wastewater has been proposed. The model incorporates reaction rate of urea hydrolysis and takes into account the effects of backmixing on the reactor performance. The model provides temperature and concentration distribution of different components along the height of reactor. The predicted data of the model were consistent with the plant data indicating the validity of the model. The impact of different parameters on the performance of urea hydrolyzer has been examined. The result of this work showed that an increase in inlet temperature of wastewater and steam flow rate would improve the urea removal efficiency.     

Urea hydrogen peroxide determination in whole blood using europium tetracycline probe

We introduce the use of a lanthanide complex, tetracycline-europium, for the clinical diagnosis of urea hydrogen peroxide in human whole blood. The values obtained agree with the urea concentration variation verified in 49 patients, including 12 predialysis, 12 peritoneal, and 15 dialysis subjects, and 10 controls. This method is noninvasive and can help in the identification of renal and cardiac diseases.     

8mol/L脲中rhIL-3含量的测定

为解决8mol／L脉中rhIL－3的定量问题,以卵清蛋白作内标,进行常规SDS－PAGE后,作激光灰度扫描,并计算rhIL－3和卵清蛋白的峰面积,发现两种蛋白峰面积的比值与rhIL－3浓度在0．2－1．0mg／ml间呈良好线性关系。查标准曲线可以计算出8mol／L脲中rhIL－3的含量。重复性测定表明该法具有较好的重现性。     

Denaturing Urea Polyacrylamide Gel Electrophoresis (Urea PAGE)

Urea PAGE or denaturing urea polyacrylamide gel electrophoresis employs 6-8 M urea, which denatures secondary DNA or RNA structures and is used for their separation in a polyacrylamide gel matrix based on the molecular weight. Fragments between 2 to 500 bases, with length differences as small as a single nucleotide, can be separated using this method¹. The migration of the sample is dependent on the chosen acrylamide concentration. A higher percentage of polyacrylamide resolves lower molecular weight fragments. The combination of urea and temperatures of 45-55 °C during the gel run allows for the separation of unstructured DNA or RNA molecules.In general this method is required to analyze or purify single stranded DNA or RNA fragments, such as synthesized or labeled oligonucleotides or products from enzymatic cleavage reactions.In this video article we show how to prepare and run the denaturing urea polyacrylamide gels. Technical tips are included, in addition to the original protocol ^1,2.     

Theoretical study of flow,pressure and solute concentration in double membrane systems

A model system consisting of two rigidly held membranes in series was investigated through the application of the Kedem and Katchalsky thermodynamic single membrane flow equations. This analysis results in predictions of the steady state flow properties as well as values for the solute concentration and pressure of the internal compartment when the system is under the influence of a constant solute concentration or hydrostatic pressure gradient. It is demonstrated that although the flow properties and internal compartment pressure are complicated functions of the membrane permeability coefficients and driving gradient across the system, the relationships are greatly simplified by the explicit appearance of the internal compartment steady state solute concentration in the equations. It is shown that the steady state volume flow rate depends on the absolute value of the solute concentration in the external compartments, as well as the solute concentration gradient across the system. The properties of non-linear dependence of volume flow on concentration gradient, and rectification of volume flow are discussed and shown to be independent properties of the system. For the system under the influence of a solute concentration gradient, the internal compartment pressure can be greater or less than the ambient pressure, and depends mainly on the order in which the membranes are encountered by the volume flow. These properties are qualitatively correlated with certain available experimental observations in biological systems.     

Urea and methylamine effects on rabbit muscle phosphofructokinase. Catalytic stability and aggregation state as a function of pH and temperature

The effects of urea and several methylamine solutes on the catalytic stability and aggregation properties of rabbit muscle phosphofructokinase were assessed at physiologically realistic concentrations of the solutes under several pH and temperature regimes. The loss of catalytic activity observed under conditions of pH-induced cold lability was significantly reduced in the presence of trimethylamine-N-oxide, N-trimethylglycine and N-methylglycine (order of decreasing effectiveness). The concentration-dependent methylamine stabilization of the enzyme, seen with as little as 50 mM trimethylamine-N-oxide, was accompanied by increased aggregation of the enzyme to molecular weights greater than the tetramer (polytetramer) as solute concentration was raised to 400 mM. At pH 6.5-6.7 and 25 degrees C, concentrations of urea greater than 25 mM promoted a time-dependent inactivation of the enzyme which was enhanced at lower temperatures. The urea sensitivity of the enzyme exhibited with 0.8 M urea for 1 h at pH 8.0 did not result in measurable inactivation. The fluorescence emission wavelength maximum of the enzyme was shifted to longer wavelengths and the fluorescence intensity was increased as pH was lowered to 7.0, suggesting the occurrence of a protein conformation change as specific amino acid residues of the tetramer became protonated. Measurements of enzyme light scattering indicated that perturbation by urea was correlated with tetramer dissociation, which was irreversible by dialysis at 25 degrees C. The urea and methylamine influences on phosphofructokinase activity and structure were not counteracting. The synergistic interactions among pH, temperature, and solutes observed with phosphofructokinase are compared to effects on other associating-dissociating protein systems in order to evaluate possible mechanisms of action of these low molecular weight solutes.     

Activation of Integrins by Urea in Perfused Rat Liver

High concentrations of urea were shown to induce a paradoxical regulatory volume decrease response with K⁺ channel opening and subsequent hepatocyte shrinkage (Hallbrucker, C., vom Dahl, S., Ritter, M., Lang, F., and Häussinger, D. (1994) Pflügers Arch. 428, 552–560), although the hepatocyte plasma membrane is thought to be freely permeable to urea. The underlying mechanisms remained unclear. As shown in the present study, urea (100 mmol/liter) induced within 1 min an activation of β₁ integrins followed by an activation of focal adhesion kinase, c-Src, p38^MAPK, extracellular signal-regulated kinases, and c-Jun N-terminal kinase. Because α₅β₁ integrin is known to act as a volume/osmosensor in hepatocytes, which becomes activated in response to hepatocyte swelling, the findings suggest that urea at high concentrations induces a nonosmotic activating perturbation of this osmosensor, thereby triggering a volume regulatory K⁺ efflux. In line with this, similar to hypo-osmotic hepatocyte swelling, urea induced an inhibition of hepatic proteolysis, which was sensitive to p38^MAPK inhibition. Molecular dynamics simulations of a three-dimensional model of the ectodomain of α₅β₁ integrin in water, urea, or thiourea solutions revealed significant conformational changes of α₅β₁ integrin in urea and thiourea solutions, in contrast to the simulation of α₅β₁ in water. These changes lead to an unbending of the integrin structure around the genu, which may suggest activation, whereas the structures of single domains remained essentially unchanged. It is concluded that urea at high concentrations affects hepatic metabolism through direct activation of the α₅β₁ integrin system.     

罗氏Cobas c501检测系统尿素分析测量范围的验证及评价

目的:核实并评价罗氏Cobasc501检测系统尿素分析测量范围。方法:主要参照美国临床实验室标准化委员会(NCCLS)指南文件EP6-P的要求,收集含高值待测物的新鲜病人血清,按一定比例混合、离心,计算混合物的浓度并将之作为高值样品(H),与经同样处理获得的低值样品(L)分别按5L、4L+1H、3L+2H、2L+3H、1L+4H、5H的关系配制,形成系列样品,在罗氏Cobasc501检测系统上对各样品的尿素进行检测,每个样品检测4次,数据进行回归分析。结果:回归方程为y=0.9889x+0.19,b=0.9889,介于0.97～1.03之间,ta小于t0.05,说明截距与0无显著性差异,回归直线事实上通过零点。结论:罗氏Cobasc501检测系统检测尿素的分析测量范围为0.7～49.9mmol/L,宽于厂家提供的分析测量范围0.5～40.0mmol/L,完全符合临床检验要求。     

The Erythrocyte Urea Transporter UT-B

During the past decade significant progress has been made in our understanding of the role played by urea transporters in the production of concentrated urine by the kidney. Urea transporters have been cloned and characterized in a wide range of species. The genomic organization of the two major families of mammalian urea transporters, UT-A and UT-B, has been defined, providing new insight into the mechanisms that regulate their expression and function in physiological and pathological conditions. Beside the kidney, the presence of urea transporters has been documented in a variety of tissues, where their role is not fully known. Recently, mice with targeted deletion of the major urea transporters have been generated, which have shown variable impairment of urine concentrating ability, and have helped to clarify the physiological contribution of individual transporters to this process. This review focuses on the erythrocyte urea transporter UT-B.