基于动态光散射的溶菌酶水力学直径研究

采用Zeta电位和粒度分析仪测量了溶菌酶的水力学直径,研究了pH值、离子强度和脲浓度对其大小的影响.随着 pH值增加,溶菌酶的水力学直径呈” W”形分布;在极端的碱性条件下,溶菌酶水力学直径随离子强度的增加而显著变大;中性pH值时,水力学直径随离子强度的增加变化不大.脲对溶菌酶具有双重作用,随着溶液中脲浓度的增加,溶菌酶的水力学直径先减小后增大.结果表明,动态光散射技术可以很好地应用于研究蛋白质分子的均一性和稳定性,同时也可以通过水力学直径来表征pH值、离子强度和脲对溶菌酶的影响.     

热变性对蛋白质结构及泡沫行为的影响

以牛血清白蛋白(BSA)和鸡蛋白蛋白(albumin)为模型蛋白,研究了热变性对蛋白质起泡性能和分子结构的影响. 结果表明,热变性后的BSA起泡能力下降,泡沫稳定性有增强的趋势. 热变性使BSA分子表面巯基含量下降,分子之间发生缔合,表面疏水性下降. 而albumin在热变性后的起泡能力及泡沫稳定性都大大提高,热变性使albumin分子展开,表面巯基含量增加. 实验证明,蛋白质分子的表面疏水性是决定其起泡能力的重要因素之一,蛋白质分子之间的相互作用对泡沫的稳定性有很大的影响.     

反胶团萃取蛋白质特性的研究

实验将一种阴离子表面活性剂（AOT）和一种阳离子表面活性剂（Aliquat336）分别溶于异辛烷（isooctane）中，构成了两种不同的反胶团体系．通过用两种不同的反胶团溶液萃取六种蛋白质的实验，研究了水相pH值及离子强度对反胶团体系中水含量Wo和蛋白质萃取率影响的规律．实验发现不论哪种反胶团体系，水相pH值对Wo的影响都不大，但pH值却对蛋白质萃取率有很大的影响，对AOT反胶团体系而言，随着pH值的降低，蛋白质的萃取率升高；对Aliquat336反胶团体系而言，随着水相pH值的降低，蛋白质的萃取率下降．随着离子强度的增大，AOT反胶团体系的水含量大幅度地降低；而对Aliquat336体系水含量的影响很小，但水相离子强度对蛋白质萃取率的影响是相同的，随着离子强度的增大，两种体系对蛋白质的萃取率均下降。     

表面活性剂辅助蛋白质体外折叠：分子模拟

采用分子模拟方法考察表面活性剂与蛋白质分子之间的相互作用及其对蛋白质折叠过程热力学特性的影响，蛋白质分子构建采用HP模型并引入了方阱类势函数.模拟结果显示：模型蛋白分子的某些折叠中间态会陷入局部能量最低状态而无法完成折叠;弱疏水性表面活性剂对模型蛋白的稳定性影响小，但可有效地帮助处于局部能量最低状态的蛋白折叠中间态通过能量壁垒而实现折叠;强疏水性表面活性剂则可与蛋白质形成高稳定性的复合物而阻止折叠的进行，需将其脱除才能使折叠过程重新开始.模拟结果还显示：表面活性剂的加入会使蛋白质折叠中间态更加丰富，从而能够光滑折叠过程中的能量阱;表面活性剂与变性环境对于蛋白质的折叠具有协同效应.模拟结果与文献报道的实验结果具有一致性，显示分子模拟的方法在揭示蛋白质折叠过程的微观机理以及表面活性剂类折叠助剂的分子设计方面有很好的应用前景.     

蛋白质-表面活性剂组装结构的分子模拟

采用Langevin分子动力学方法模拟β模型蛋白与表面活性剂在溶液中形成的各种组装结构,考察了表面活性剂疏水性强度与浓度对蛋白质分子构象的影响.结果显示：弱疏水性表面活性剂可以在蛋白质表面自组装形成限制性空间,使被包覆的蛋白质的立体结构更为稳定;强疏水性的表面活性剂则可以与蛋白质疏水核心区的疏水基团形成复合物,而使蛋白质的立体结构被破坏,即蛋白质发生去折叠.上述模拟可再现相关实验结果,其展现的蛋白质结构转换微观图景对于表面活性剂的分子设计及其应用于生物加工过程具有指导作用.     

pH值和离子强度对空间质量作用模型参数的影响

以牛血清白蛋白（BSA）为模型蛋白质研究了pH值和离子强度对空间质量作用模型参数的影响。通过静态吸附实验确定了不同pH值和离子强度条件下BSA在阴离子交换剂DEAE-Spherodex M上的吸附平衡,利用色谱实验及非线性最小二乘法确定模型参数。研究发现,只有在pH值远大于BSA等电点时,蛋白质的特征电荷数和空间因子才为常数;离子交换平衡常数不仅是pH值的函数,也受到液相离子强度的影响。     

表面活性剂辅助重组蛋白质复性

以重组人溶菌酶（rhLys）与重组β-甘露聚糖酶（rMan）为体系,综合采用活性测定、非还原性SDS-PAGE以及荧光发射光谱分析等方法研究了十六烷基三甲基溴化铵（CTAB）、CTAB与β-环糊精（β-CD）组成的人工分子伴侣以及其他种类复性助剂对重组蛋白质复性过程的影响.结果表明CTAB及人工分子伴侣均可有效地辅助rhLys复性,且rhLys与鸡卵清溶菌酶（Lys）呈现出类似的复性过程特性;人工分子伴侣可显著地提高rMan在高浓度下的复性率;表面活性剂带电性质、表面活性剂与蛋白质的摩尔比以及变性蛋白质的浓度等是影响复性率及复性产品分布的主要因素.这些结果对于此类复性技术应用于重组蛋白体系时的工艺选择和优化提供了重要的依据和参考.     

阳离子反胶团体系萃取牛血清白蛋白

采用一种新的阳离子反胶团体系(CTAB/异辛烷-正戊醇),研究了反胶团萃取牛血清白蛋白(BSA).用单变量法考察了表面活性剂浓度、水相pH值、离子种类和浓度、萃取时搅拌速率和油水比对BSA萃取率的影响.实验表明,静电作用力是该萃取过程的主要动力,随水相pH值增大,BSA的萃取率逐渐升高;对于不同种类的离子,基本随其浓度增大,萃取率下降.在优化的操作条件下,BSA萃取率可达98%以上,因此,CTAB/异辛烷-正戊醇反胶团体系适合BSA的萃取.     

磁性微球与蛋白质相互作用的微量热研究

以牛血清白蛋白(BSA)为生物模型,采用微量热法自动跟踪磁性微球与BSA相互作用的全过程,研究了磁性微球与BSA相互作用的微量热;采用分光光度法测定了磁性微球所吸附的蛋白质容量;建立了磁性微球表面性质与蛋白质吸附容量的关系.结果表明,微量热法与传统的光度法所得结果大致相当,即相互作用的热越多,吸附蛋白质的容量越大,而且偶联羧基的磁性微球比无官能团的微球具有更大的吸附热和吸附容量.     

表面活性剂与蛋白质相互作用的研究进展

综述了表面活性剂与蛋白质的相互作用以及该领域最新的研究方法和研究成果。从荧光技术在研究表面活性剂－蛋白质相互作用中的应用为出发点，介绍了表面活性剂与蛋白质相互作用所形成的复合物的结构及相互作用过程中蛋白质结构的变化；在阐述表面活性剂－蛋白质相同电荷混合体系及相反电荷混合体系的不同相行为特征的同时，介绍了NMR弛豫技术和冷冻蚀刻电镜在研究表面活性剂与蛋白质相互作用中的应用；表面活性剂－蛋白质混合溶液的界面吸附行为的研究以非离子表面活性剂与蛋白质的相互作用为主线，介绍了表面活性剂－蛋白质混合溶液界面吸附的2种机理，以及LB膜技术和流变学研究方法在研究表面活性剂－蛋白质相互作用中的应用。     

The role of hydrodynamic conditions and solution chemistry on protein fouling during ultrafiltration

This study investigates the effect of hydrodynamic conditions and solution chemistry on protein fouling during ultrafiltration. Drastic flux reduction was observed at high initial flux and/or low cross-flow velocity. A limiting flux existed during BSA filtration, beyond which membrane flux cannot be sustained. Further increase in pressure over the limiting value did not enhance the stable flux. The rate and extent of BSA fouling were also strongly dependent on the feedwater composition, such as BSA concentration, pH, and ionic strength. Foulant concentration had no effect on the stable flux, although the rate approaching to the stable flux increased proportionally with increasing foulant concentration. Fouling was most severe at the isoelectric point of BSA (pH 4.7), where the electrostatic repulsion between foulant molecules is negligible. Membrane fouling became less severe at pHs away from the isoelectric point. Increasing ionic strength at pH 3.0 promoted severe fouling likely due to electric double layer (EDL) compression. On the other hand, the flux behavior was insensitive to salt concentration at pH 4.7 due to the lack of electrostatic interaction. At a solution pH of 5.8, effect of ionic strength on long-term flux behavior was directly opposite to that on the transient behavior. While the long-term flux was lower at higher ionic strength due to EDL compression, the transient behavior was also affected by the BSA retention of the membrane.     

Rheo-kinetics of bovine serum albumin in catanionic surfactant systems

The effects of catanionic surfactant systems consisting of mixtures of cationic cetyltrimethylamonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) on the rheological properties and kinetics of bovine serum albumin (BSA) were investigated. The ionic strength of the solution was varied by using different mixing ratio of SDS and CTAB. Gelation curves observed in dynamic viscoelastic measurements were fitted with gelation kinetics models to describe the gelation under isothermal and non-isothermal conditions. Overall, the gelation of BSA in cationic-rich solutions was found to be more energetically favorable when compared with BSA solvated in anionic-rich solutions. Consequently, highest gel temperature (T_gel) and time (t_gel) were observed for anionic-rich solutions with SDS/CTAB molar ratio of 4.0 (i.e., SDS/CTAB=4.0), while lowest gel temperature and time were found for cationic-rich solutions with SDS/CTAB molar ratio of 0.25 (SDS/CTAB=0.25). BSA in equal molar ratio of the mixed surfactants (SDS/CTAB=1.0) showed a gel temperature and time in the halfway between the anionic and cationic-rich regions. Interestingly, under isothermal and non-isothermal conditions, BSA in equimolarly mixed and anionic-rich solutions showed a heat-dependent protective effect against thermal denaturation and gelation. The protective effect on BSA gelation in equimolar and anionic-rich solutions was diminished by increasing the catanionic concentration under non-isothermal conditions, while under isothermal conditions, protective effect on BSA gelation increased with catanionic concentration. On the other hand, cationic-rich solutions did not protect BSA from thermal denaturation and gelation, and therefore the gelation rate increased with catanionic concentration in all heating conditions examined.     

Thermal and mechanical properties of plastics molded from urea-modified soy protein isolates

Soy protein has been considered as a potential alternative of some petroleum polymers in the manufacture of plastics. The purpose of this investigation was to characterize the thermal and mechanical properties of plastics made from urea-modified soy protein. Soy protein isolate was separated from the defatted soy flour, modified with various urea concentrations, and compression-molded into plastics. Differential scanning calorimetry showed that the temperatures of denaturation and the enthalpies of denaturation of the modified soy protein decreased as urea concentrations increased above 1 M. At the same urea concentration, molded plastics made from the modified soy proteins showed a similar temperature of denaturation as the modified soy protein, but a lower enthalpy of denaturation. Tensile strength and Young's modulus of the molded plastics from the modified soy proteins increased as urea concentration increased and reached their maximum values at 8 M urea modification. Both storage modulus and glass transition temperature of the plastics from the modified soy proteins increased as urea concentration increased. The plastics made from the 2 M urea-modified soy proteins showed improvements in elongation, tough fracture behavior, and water resistance. The urea may function as a denaturant, a plasticizer, and a filler.     

Effect of Nonionic Surfactant on the Micro‐Emulsifying Water in Silicone Media

Reverse micro‐emulsion dyeing technology shows a high dye uptake and fixation rate, and effectively decreases the amount of waste water in the textile industry. However, the influence of surfactants and co‐surfactants on micro‐emulsifying water in reverse micro‐emulsions has not been investigated. In this study, the micro‐emulsifying mechanism in silicone media and the influence of nonionic surfactants and co‐surfactants on micro‐emulsifying water have been investigated. The results show that a large amount of water can be emulsified using alcohol‐polyoxyethylene ethers, especially under 3–5 ethylene oxide groups in molecular structure. As co‐surfactant, alcohol which contains 4–9 carbon chains could spontaneously form reverse micro‐emulsions in silicone media. The effects of solution pH and ionic strength on the amount of emulsified water were also evaluated. The results show that a large amount of water could be emulsified in silicone media at solution pH 2–9. Meanwhile, the amount of emulsified water decreased with increasing ionic strength. Thus, the optimum conditions for water emulsification are low ionic strength and pH between 2 and 9.     

离子强度和溶质浓度对蛋白质在Q Sepharose FF中吸附动力学的影响

采用孔扩散模型, 模拟不同盐浓度和不同蛋白质初始浓度条件下,吸附牛血清白蛋白(BSA)的动态吸附曲线并获得孔扩散系数;考察了离子强度和溶质浓度对蛋白质在阴离子交换剂Q Sepharose FF中吸附动力学的影响.结果表明,蛋白质的孔扩散系数随初始浓度的增大而下降;在氯化钠浓度小于0.10 mol•L^-1的范围内,蛋白质的孔扩散系数随着盐浓度的增加而增大,但当盐浓度增大到0.15 mol•L^-1时又有所降低,表明存在着一个最佳的离子强度,使蛋白质的孔扩散系数最大.     

A study on the adsorption behavior of protein onto functional microspheres

Adsorption has been investigated using bovine serum albumin (BSA) as the model protein and sulfonated microspheres as the matrix. The adsorption appears to be sensitive to time, pH, and ionic strength, and the presence of sulfonate groups can play important roles in this process, increasing the adsorption rate and the amount of protein adsorbed, as well as influencing the interaction of BSA molecules. Fittings from Langmuir's and Freundlich's isotherms indicate that the actual adsorption becomes more complicated than the ideal process, due to the presence of intermolecular interactions of BSA. The determinations under different pH conditions (pH 2.2, 4.3, 7.4) show that near the isoelectric point of BSA (pI 4.7), the amount of protein adsorbed reached a maximum value, and a higher or lower pH resulted in a significant decrease in amount adsorbed. The effect of ionic strength is, however, closely associated with the operating conditions. Copyright © 2005 Society of Chemical Industry     

Thermal properties and adhesiveness of soy protein modified with cationic detergent

This research studied the effects of cationic detergents on the adhesiveness and thermal properties of soy protein isolate (SPI). Three cationic detergents, hexadecyltrimethyl ammonium bromide, ethylhexadecyldimethyl ammonium bromide (EDAB), and benzyldimethylhexadecyl ammonium chloride, each at concentrations of 1.3, 2.6, 5.2, and 7.8 mM, were used to modify SPI. The effect of pH at selected EDAB concentrations was also studied. Results showed that both detergent concentration and pH had significant effects on the adhesiveness of modified SPI. SPI modified with detergent at a concentration of 2.6 mM yielded the greatest dry tensile strength and water resistance, which indicated that a moderate protein denaturation might be favorable to the adhesion of SPI. Both modified and unmodified SPI showed greater adhesive strength at their optimal pH values. Modified SPI showed greatest adhesive strength at pH 7, whereas unmodified SPI showed greatest adhesive strength at pH 4.5; the tensile strength of modified SPI was greater than that of unmodified SPI. The protein-denaturation temperature and the enthalpy of modified SPI adhesives were also analyzed by using DSC. Denaturation of the native structure of SPI increased as detergent concentration increased.     

Effects of Ionic Environments on Bovine Serum Albumin Fouling in a Cross‐Flow Ultrafiltration System

The influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a cross‐flow ultrafiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001 M and 0.1 M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant.     

Adsorption of dissolved organics from industrial effluents on to activated carbon

Industrial effluents usually include multicomponent organic solutes. The optimum pH for adsorption of a specific industrial effluent on activated carbon should be determined experimentally because, in general, more than one mechanism is involved. A series of experiments was conducted to establish the influence of the initial hydrogen ion concentration on carbon adsorption of organic solutes. For these studies, powdered activated carbon was used, and the water systems studied included both single component pure organic compounds as well as multicomponent organic wastes. Results indicate that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. In general, the degree of ionisation is the controlling factor for adsorption of ionic organic solutes on activated carbon. Adsorption reaches a maximum at the point of least ionisation of the adsorbate. As the organic compounds become more complex (i.e. longer hydrocarbon chains, higher molecular weights, increased branching), the electrical adsorption forces between activated carbon and ionic organic solutes will govern. Anionic surfactants meet with decreased electronegative repulsive forces at low pH levels, which increase the effectiveness of carbon adsorption. However, the adsorption of a cationic surfactant is increased by an increase in the electronegative carbon surface at high pH levels. When ionic organic solutes become much more complex, like a polymer, the effects of both ionisation and electrical adsorption forces become less important. Instead, the adsorption rate will be controlled by the extent of hydrolysis caused by the pH adjustment. For non-ionic organic solutes, chemical reaction(s) between the adsorbate and the added chemical (acid or base) for pH adjustment is an important controlling factor. Again, hydrolysis is responsible for the breakdown of larger size molecules to smaller sizes. Then an increase in adsorption rate with decreasing molecular weight of adsorbate is expected.     

A Dynamic Light Scattering Study on the Complex Assembly of Glycinin Soy Globulin in Aqueous Solutions

In this work, the complex assembly of one of the major storage proteins in soybean, glycinin, was analyzed using dynamic light scattering, from the hydrodynamic diameter of assembled forms in solution. The protein concentration and temperature were maintained constant at 10⁻¹% w/w and 20 °C, respectively, and the pH was 7.6, 7.0 and 3.0. By analyzing the intensity and volume size distributions, a complex equilibrium between self-assembled forms could be determined. At pH 7.6 and an ionic strength of 0.5 M, where the self-assembly of glycinin has been widely reported in the literature, the DLS technique revealed an equilibrium between different assembled forms, that shifted towards the 11S form. At a lower ionic strength for pH 3.0 or 7.0, the 7S form predominated. The hydrodynamic diameter evolved differently upon heating, depending on pH and ionic strength. For pH 7 (I = 0.05) and 7.6 (I = 0.5) a significant increase in d_H was observed at a temperatures of 55 and 70 °C, respectively, which were significantly lower than the denaturation onset temperatures as determined by DSC. No changes in d_H nor a transition endotherm were observed at pH 3.