高压和酶解对热变性大米蛋白溶解及结构特征的影响(英文)

研究了100MPa高压和酶解处理对热变性大米蛋白溶解性和分子结构特征的影响。结果显示:高压处理后再用Alcalase(碱性蛋白酶)酶解可使大米蛋白的溶解性由单纯酶解时的58.9%提高到75.33%;SE-HPLC(高效液相凝胶色谱法)分析显示,高压处理可使57~105ku的大分子蛋白质溶出,且随着酶解时间延长,该组分消失,4.4和2.0ku组分含量增加,而非高压处理者没有大分子的溶解;FTIR(傅里叶红外光谱)分析显示,高压处理的样品中β-折叠和β-转角结构占主导地位;SEM(扫描电子显微镜)分析表明,高压处理使致密的大米蛋白体结构变得疏松。以上结果表明,高压处理改变了蛋白的空间结构,进而改变蛋白的酶解位点,从而提高了大米蛋白的溶解性。     

超声波处理对脱脂麦胚分离蛋白结构的变化研究

应用傅里叶红外光谱(FTIR)、荧光光谱研究超声处理对脱脂麦胚分离蛋白(DWGP)结构的变化,建立DWGP高效酶解与其结构变化之间的关系.研究发现,超声处理均可提高DWGP的酶解效果,特别是经超声功率600 W、时间10 min处理后,酶解液抑制活性与对照组相比提高了23.96%.通过荧光光谱发现,超声作用改变DWGP溶液荧光强度,适当超声处理可使蛋白分子伸展、生色基团外露,有助于蛋白酶解后获得活性更高的抑制肽.采用对FTIR谱酰胺I带进行曲线拟合的方法,定量分析了不同超声功率、时间对DWGP二级结构的影响,发现超声作用使β-折叠相对含量下降而β-转角含量增加,这可能是DWGP酶解后获得高效抑制肽的主要原因.     

紫外光谱法研究环糊精/精(口恶)唑禾草灵超分子复合体

采用紫外光谱法研究了β-环糊精(β-CD)、羟丙基-β-环糊精(HP-β-CD)和部分甲基化β-环糊精(RAMEB)与精(口恶)唑禾草灵(FE-p)间的超分子作用.在体积比为1:4的乙醇-水溶剂中,在298.15～318.15K的温度范围内,3种环糊精均能与FE-p形成稳定的1:1型的超分子复合体,其结合常数值大小依次是KRAMEB>KHP-β-CD＞KβCD,且随着温度的升高而降低.经过计算,热力学参数△G,△H和△S均为负值,说明结合反应是放热反应且能自发进行,焓变是形成超分子复合体的主要驱动力,符合熵焓补偿效应.     

表面增强拉曼散射探测细胞酶的活性

本文以5-溴-4-氯-3-吲哚基-β-D-吡喃半乳糖苷为底物,探测细胞结构中β-半乳糖苷酶的活性。作为β-半乳糖苷酶的底物,5-溴-4-氯-3-吲哚基-β-D-吡喃半乳糖苷在细胞β-半乳糖苷酶酶解作用下,形成靛蓝染料衍生物,在贵金属表面具有较强的表面增强拉曼散射。这种通过表面增强拉曼光谱探测细胞酶活性的方法,与高速拉曼线扫描相结合,可以快速地评估细胞种群的酶活性。     

面粉中蛋白质二级结构的红外光谱研究

测定了不同温度下面粉蛋白质酰胺Ⅲ带的一维红外光谱,二阶导数红外光谱和去卷积红外光谱。研究发现:随着测定温度的升高,面粉蛋白质中的α-螺旋结构的、β-转角结构、无规卷曲结构和β-折叠结构红外吸收强度均有所增加。进一步研究了面粉蛋白质酰胺Ⅲ带的二维红外光谱。研究发现:随着测定温度的升高,面粉中蛋白质酰胺Ⅲ带的红外吸收强度变化快慢趋势是:1312cm-1(α-螺旋结构)1285cm-1(β-转角结构)1260cm-1(无规卷曲结构)1229cm-1(β-折叠结构)。     

六种生物药物分子的高分辨太赫兹光谱研究

利用太赫兹时域光谱技术,在77～295 K之间,分别测量了两种异黄酮(金雀异黄酮和鹰嘴豆芽素A)、两种瘦肉精(盐酸克伦特罗和沙丁胺醇)和两种人参皂苷(Rg2和Rg3)等三类药物生物分子随温度变化的低频振动光谱,发现结构和功能相似的同类样品在室温环境下的太赫兹光谱均存在明显的不同。当温度从295 K冷却到77 K,测量样品的特征峰增加,鹰嘴豆芽素A可以观察到13个高分辨的特征吸收峰;并伴随线宽变窄,可以为1.9×10-5 mol用量的人参皂苷20-(R)-Rg3提供较准确的吸收峰。得到的高分辨太赫兹指纹谱为快速、无损鉴定该类药物生物分子提供一种可靠的新方法。     

串联酶解耦合超微粉碎法对蔗渣酶解的促进作用

报道了一种新颖的串联酶解(先酶I后酶II)耦合超微粉碎方法,并系统研究了其对蔗渣酶水解的促进作用. 通过对三种酶解方法(单酶I、单酶II、先酶I后酶II) 的比较发现,串联酶解对蔗渣酶解最为有效. 超微粉碎能破坏蔗渣细胞结构,使纤维素充分暴露出来便于酶解.在串联酶解耦合超微粉碎模式下,蔗渣在反应温度50 oC,pH=4.8,酶I(7.5 FPU/g底物)和酶II(5.0 FPU/g底物),摇床速率1200 r/min条件下反应72 h后,酶水解能得到65%的还原糖浓度,其中葡萄糖选择性为90.1%.     

热处理对蛋清卵类粘蛋白过敏原性及构象的影响

采用酶联免疫吸附法(ELISA)、圆二色谱(CD)、ANS荧光探针和紫外光谱(UV)系统研究了热处理对蛋清卵类粘蛋白过敏原性及构象的影响。结果显示,加热处理卵类粘蛋白的过敏原性降低,且随加热温度升高和加热时间延长,不断降低。经不同温度热处理后的卵类粘蛋白二级结构的α-螺旋,β-折叠,β-转角和无规卷曲之间相互转化,分子有序性降低;卵类粘蛋白的表面疏水性随加热温度的升高而降低;随加热的温度的升高,具有紫外吸收的氨基酸残基逐渐暴露,最大吸光度逐渐增大。由此可以推断,卵类粘蛋白的构象改变导致其过敏原性变化。     

诺氟沙星与环糊精的超分子体系

研究了诺氟沙星与β-环糊精(简称β-CD)及其两种衍生物羟丙基-β-环糊精(简称Hp-β-CD)、甲基-β-环糊精(简称Me-β-CD)形成的超分子体系.利用荧光光谱法测定了超分子体系的包结常数和包结比,及其热力学参数.诺氟沙星与3种环糊精均形成1∶1稳定的包合物,诺氟沙星与β-CD、Me-β-CD及Hp-β-CD作用...     

应用圆二色光谱研究电场对辣根过氧化物酶二级结构的影响

辣根过氧化物酶(HRP)经不同强度的电场处理,用圆二色光谱研究了电场对辣根过氧化物酶二级结构的影响.结果表明:在1.0～6.0 kV·cm-1范围,不同强度的电场对辣根过氧化物酶的α-螺旋、β-折叠、β-转角及无规卷曲相对含量的影响程度不同.与对照组相比,处理组的α-螺旋、β-转角和无规卷曲含量降低,降幅范围分别为0.3%～11.4%,1.7%～15.3%和0.9%～20.4%;β-折叠含量增加,增幅范围为0.9%～82.7%.电场作用具有使辣根过氧化物酶的二级结构中α-螺旋、β-转角和无规卷曲向β-折叠转化的趋势.研究结果对解释电场处理种子生物效应具有重要意义.     

Molecular Dynamics Simulation of Temperature-dependent Flexibility of Thermophilic Xylose Isomerase

构建了嗜热栖热菌木糖异构酶与底物木糖的复合物模型,并运用NAMD2.5软件对其在300 和360 K下进行了10 ns的分子动力学模拟. 对该酶的回旋半径、亚基间相互作用及残基柔性进行了计算与统计分析,确定了该酶在360 K时柔性残基及区域. 研究发现与300 K相比,360 K时木糖异构酶中B-因子增幅较大的残基主要可分为两组：一组位于催化结构域,是由残基55～80组成的helex-loop-helix区域,另一组位于其亚基界面上. 研究表明高温下该酶催化结构域回旋半径增加,可能加速了活性中心的运动从而有利于D-木糖的异构化反应.在360 K时亚基界面上减少了8个氢键和5个离子对,这可能也是高温下其整体结构刚性下降并且活性升高的主要原因,该结果也对文献报道的该酶E372G突变体冷适应的实验现象进行了解释. 研究结果揭示了嗜热栖热菌木糖异构酶温度和结构柔性之间的关系.     

Kadomtsev-Petviashvili (KP) Burgers equation in a dusty plasmas with non-adiabatic dust charge fluctuation

The nonlinear dust acoustic waves in a dusty plasmas with the combined effects of non-adiabatic dust charge fluctuation and higher-order transverse perturbation are studied. Using the perturbation method, a Kadomtsev-Petviashvili (KP) Burgers equation that governing the dust acoustic waves is deduced for the first time. A particular solution of this KP Burgers equation is also obtained. It is show that the dust acoustic shock waves can exist in the KP Burgers equation.Received: 18 March 2003, Published online: 15 July 2003PACS: 52.35.Sb Solitons; BGK modes - 52.35.Mw Nonlinear phenomena: waves, and nonlinear wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)     

Electron correlation in two-dimensional systems: CHNC approach to finite-temperature and spin-polarization effects

Applying the classical-map hypernetted-chain method (CHNC) developed recently by Dharma-wardana and Perrot, we have studied the temperature and spin-polarization effects on electron correlation in the uniform quantum two-dimensional gas (2DEG) over a wide range of temperature T and spin-polarization ζ. The quantum fluid at the temperature T is mapped to a classical fluid at the temperature T_cf given by T_cf²=T²+T_q², where the quantum temperature T_q is determined by comparing the calculated correlation energy to that of Monte Carlo results for the fully spin-polarized quantum system at zero temperature. By the iterative solution of the modified HNC equation and the Ornstein-Zernike equation, we have obtained the pair distribution function (PDF) and correlation energy for the two-component classical 2DEG with a classical fluid temperature T_cf. The anti-parallel bridge function B₁₂(r) appearing in the modified HNC equation is determined by using the Monte Carlo correlation energy at T=0 or STLS (Singwi-Tosi-Land-Sjölander) result at T>0 and the numerical solution to the Percus-Yevick (PY) equation for the system of hard disks. By calculating the Pauli potential, the bridge function, PDFs, structure factors and correlation energy, we have shown that in some cases, the properties of the uniform quantum 2DEG depend remarkably on the temperature and spin-polarization.     

人参皂苷Rg3的拉曼光谱研究

人参皂苷是人参的有效化学成分,其中人参皂苷Rg3因具有显著的生理活性而备受关注。运用拉曼光谱的方法,对人参皂苷Rg3的两种异构体20-(R)-Rg3和20-(S)-Rg3进行了测量和分析。因20位羟基空间位置不同,20-(R)-Rg3与20-(S)-Rg3相比,归属于亚甲基的振动峰发生了明显的变化,表明两种异构体的堆积方式不同。归属于CC振动的1674cm-1峰的强度明显降低,表明在20-(S)-Rg3中,C27和C28较20-(R)-Rg3处于分子内部。对比拉曼光谱还发现,这一对异构体中糖环的空间结构基本相同。两种异构体拉曼光谱的明显差异,使得拉曼光谱技术成为鉴别人参皂苷Rg3异构体的一种快速、简便的分析方法。     

A molecular dynamics study of effective parameters on nano-droplet surface tension

The main purpose of this paper is to numerically study the effect of droplet radius, temperature, and surface wettability on droplet surface tension. Moreover, the validity of Young-Laplace equation (Y-L) for nano-droplet is examined. Simulations of droplet surrounded by its vapor and droplet on solid surface are carried out and the results are compared to each other in order to comprehend the role of surface wettability on droplet surface tension. The pair potential for the liquid-liquid and liquid-solid interaction is considered using Lennard-Jones model. Different numbers of atoms and surface wettabilities are employed to generate droplet of different radiuses. In addition, contact angle of droplet on solid surface is computed. Pressure tensor and density profile is locally calculated. Furthermore, liquid pressure is evaluated far from the interface using the virial theorem and gas pressure is obtained using an equation of state. In order to calculate the surface tension, two different approaches are employed; Young-Laplace equation and direct molecular dynamics (MD) simulation. The surface tension increases with increase in droplet radius and it is seen that the surface wettability does not directly influence the surface tension.     

Integral equation theory of a one dimensional hard-ellipse fluid between hard walls

Density functional theory is used to study the structure of a one dimensional fluid model of hard-ellipse molecules with their axes freely rotating in a plane, confined between hard walls. A simple Hypernetted chain (HNC) approximation is used for the density functional of the fluid and the integral equation for the density is obtained from the grand potential. The only required input is the direct correlation function of the one dimensional hard-ellipse fluid. For this model, the pressure, sum rule and the density at the walls are obtained. The Percus Yevick (PY), for lower density, and HNC, for higher density, integral equations are also solved to obtain the direct correlation function of hard-ellipse model introduced here. We obtain the average density at the wall as well as the radial density profile. We compare these with Monte Carlo simulations of the same model and find reasonable agreement.     

Mitogens-DPPC-vesicles interaction: A spin label ESR study

Summary The electron spin resonance spectroscopy with the spin labelling technique has been used to investigate the interaction of sonicated di-palmitoyl-phosphatidylcholine (DPPC) small unilamellar vesicles with concanavalin A (Con A), phytohemagglutinin (PHA) and staphylococcal enterotoxin B (SEB) in the temperature range 0–50°C. Conventional ESR measurements show that the addition of mitogens to the vesicles suspensions up to the number of mitogens/number of vesicles ratio of 60 increases the orientational degree of order of the lipid molecules in the gel phase and the gel→liquid-crystalline phase transition temperature. No effects on the liquid-crystalline phase have been observed, also no matter for the mitogen used. The effectiveness results in the order: ConA>SEB>PHA. Saturation transfer-ESR measurements evidence more restricted rotation of the DPPC molecules in the gel phase in the presence of Con A and SEB than in the presence of PHA if compared to pure DPPC-vesicles. The effective rotational correlation time, σ_c, of the spin label 5-SASL results about one order of magnitude higher in the presence of 60 mitogen molecules/vesicle. The ESR findings suggest a mitogen-induced increase in the packing density of lipid bilayers which is attributed to a morphological change from sonicated vesicles, with a small radius of curvature, to a more planar mesophase. Con A is more effective than SEB and PHA in inducing this process. The authors of this paper have agreed to not receive the proofs for correction.     

高压下MgO熔化特性的分子动力学模拟

利用分子动力学方法,模拟研究了高压下MgO的熔化特性．通过晶体的现代熔化理论,对MgO的分子动力学模拟熔化温度进行了修正,得到了高温高压下MgO的熔化温度．计算得到的MgO熔化曲线和已有的实验及其它理论结果在0-135 GPa进行了比较,发现修正得到的MgO熔化温度和由Lindemann熔化方程及两相方法得到的结果在压力低于15 GPa时符合很好．同时,MgO熔化模拟有效解释了一阶相变分子动力学过程中出现的过热熔化现象．     

A theory of vibrational frequency shifts revisited: application to dimers of LiH with the inert gases He,Ne, Ar and Kr

The objective of this paper is to contribute towards an understanding of the anomalous blue vibrational shifts that have been observed on forming some hydrogen bonds. It is shown that linear complexes of the LiH molecule with an inert gas atom Rg exhibit red or blue shifts of the LiH vibrational frequency depending upon whether Rg is attached to the Li or the H atom.

The shifts in the frequency of the Li–H vibration on forming the weakly bound linear complexes Li–H…Rg and H–Li…Rg (Rg?=?He, Ne, Ar, Kr) were determined by ab initio computations at the MP2/6-311++G(2d,?2p) level of theory. These frequency shifts were found to be in good agreement with predictions from a model based on perturbation theory and involving first and second derivatives U′ and U′′ of the interaction energy with respect to displacement of the Li–H bond length from its equilibrium value in the isolated molecule. Concentration of the Li–H vibrational motion in the light H atom causes U′ and U′′ to be dominated by repulsion in Li–H…Rg and by attraction in H–Li…Rg, producing blue and red shifts, respectively. The bond length changes on complexation are well predicted by U′.     

The extended third-order nonlinear Schrödinger equation and Galilean transformation

The extended third-order nonlinear Schrödinger equation and its solutions are studied on the basis of Galilean transformation and generalized Galilean invariance.Received: 15 September 2003, Published online: 12 July 2004PACS: 42.65.Tg Optical solitons; nonlinear guided waves - 52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)