Study of the anomalous particles formed during the surfactant-free emulsion polymerization of styrene

The presence of anomalous regions within polystyrene latex particles prepared in the absence of added emulsifier has been investigated. It appears that they arise through loss of monomer from particles consisting of a discrete monomer-rich region surrounded by a polymer shell. It is likely that in most cases, monomer is lost from the region on evacuation prior to electron microscope examination, although there is some evidence from γ-irradiated samples (prior to electron microscopy) that loss of monomer can also occur during storage and/or dilution of the sample. Scanning electron microscopy and carbon replication techniques have been used to determine the shapes of the voids. Gas adsorption studies and carbon replication have also served to illustrate that the presence of the regions was not due to electron-beam damage. The presence of extrusions on some samples has been attributed to incomplete loss of monomer on evacuation due to the thickness of the surrounding polymer shell.     

Proteasome function in antigen presentation: immunoproteasome complexes, Peptide production, and interactions with viral proteins

Proteasomes are the major nonlysosomal protein degradation machinery in eukaryotic cells and they are largely responsible for the processing of antigens for presentation by the MHC class I pathway. This review concentrates on recent developments in the area of antigen processing. Specialized proteasomes called immunoproteasomes and an 11S regulator of proteasomes (PA28) are induced by interferon-gamma, but it is not entirely clear why changes in proteasome structure are beneficial for antigen presentation. Different proteasome complexes have distinct subcellular distributions and subtle differences in cleavage specificity. Thus it is likely that the efficiency of production of MHC class I binding peptides varies in different locations. Immunoproteasome subunits are enriched at the ER where TAP transports peptides for association with newly synthesized MHC class I molecules. There is recent evidence to suggest that antigen presentation from viral expression vectors, or from peptides that are either delivered by bacterial toxins or derived from signal peptides, require proteasome activity for generation of the correct C-terminus of the epitope. The correct N-terminus may be generated by recently identified ER associated aminopeptidases. A number of viral protein interactions with proteasome subunits have been reported and such interactions may interfere with host anti-viral defenses and also contribute to mechanisms of cell transformation.     

Adsorption and selectivity characteristics of several human serum proteins with immobilised hard Lewis metal ion-chelate adsorbents

In this investigation, human serum has been used as an example of a crude protein mixture to define the protein binding characteristics and selectivity of several immobilised hard Lewis metal ion affinity chromatographic (IMAC) adsorbents. Specifically, the binding properties of immobilised O-phosphoserine (im-OPS) and 8-hydroxyquinoline (im-8-HQ), with immobilised iminodiacetic acid as a control system, have been investigated in combination with the hard Lewis metal ions, Al3+, Ca2+, Fe3+, Yb3+, and the borderline metal ion, Cu2+, over the pH range pH 5.5 to pH 8.0 with buffers of 0.5 M ionic strength. The same IMAC adsorbents were also investigated for their protein binding capabilities with buffers of an ionic strength of 0.06 M at pH 5.5 and pH 8.0. The binding behaviour of four "marker" proteins, namely transferrin, alpha2-macroglobulin, gammaglobulin and human serum albumin have furthermore been employed to monitor the differences in protein selectivity exhibited by these IMAC systems. The experimental findings confirm that these hard Lewis metal ion IMAC adsorbents function in a "mixed" binding mode with both coordination and electrostatic characteristics evident, depending on the ionic strength and pH of the equilibration or elution buffers. Based on a screening protocol, several members of the im-Mn+-8-HQ and im-Mn+-OPS adsorbent series have been identified with high selectivity for transferrin and alpha2-macroglobulin. These hard Lewis metal ion IMAC adsorbents thus provide attractive alternatives for selective fractionation of human serum proteins.     

Referees 1975

Notice

Referees 1975     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

朊病毒蛋白113-120序列多肽的反相液相色谱保留行为与构象稳定性的关系

朊病毒（Prion)蛋白是人和动物慢性中枢神经系统退化病的传染源,该蛋白的113－120序列被认为在其致病和传染机理中起着重要作用。以反相高效液相色谱为分析手段,研究了Prion蛋白113－120序列多肽的色谱保留行为。通过比较不同温度、不同流动相条件下该多肽色谱保留行为的变化,发现在乙腈溶液为上时,1nKw随温度的变化关系和Van′t Hoff曲线均比简单,说明该多肽在乙腈溶液中所采取的构象均较稳定,不易受温度的影响。以甲醇溶液为流动相时,具有游离末端的多肽的1nKw随温度变化关系和Van′t Hoff曲线比末端羧基和氨基分别被酰胺封闭的多肽要复杂,说明具有游离末端的多肽在甲醇溶液中所采取的构象相对较不稳定,易受环境的影响。这些结果进一步证明,113－120序列在Prion蛋白构象变化中可能起着重要作用。     

Dynamic Adsorption of Vapours by Activated Carbons and by Polymer-Derived Adsorbents: 1. Adsorption at 0% R.H.

The uptakes of volatile organic compounds from a nitrogen carrier gas at 0% R.H. onto packed beds of adsorbents have been measured by monitoring the effluent vapour concentration profile as a function of time. The profiles have been quantitatively fitted by a modified Bohart-Adams equation which was then integrated to yield the adsorbent capacities. Traditional activated carbons, carbonised macroreticular resins and a macroreticular polymer were used in the study. Performance in the dynamic tests has been related to the pore volume characteristics and surface areas determined from nitrogen adsorption isotherms. Whilst the extent of micropore filling basically increased as the sorbate boiling point increased and increased capacities reflected increased micropore volumes, these trends were interrupted by size exclusion and specific polar interaction effects.     

A new dynamic programming algorithm for the single item capacitated dynamic lot size model

We develop a new dynamic programming method for the single item capacitated dynamic lot size model with non-negative demands and no backlogging. This approach builds the Optimal value function in piecewise linear segments. It works very well on the test problems, requiring less than 0.3 seconds to solve problems with 48 periods on a VAX 8600. Problems with the time horizon up to 768 periods are solved. Empirically, the computing effort increases only at a quadratic rate relative to the number of periods in the time horizon.This research was supported in part by NSF grants DDM-8814075 and DMC-8504786.     

An MPEC approach to second-best toll pricing

This paper addresses two second-best toll pricing problems, one with fixed and the other with elastic travel demands, as mathematical programs with equilibrium constraints. Several equivalent nonlinear programming formulations for the two problems are discussed. One formulation leads to properties that are of interest to transportation economists. Another produces an algorithm that is capable of solving large problems and easy to implement with existing software for linear and nonlinear programming problems. Numerical results using transportation networks from the literature are also presented.This research was partially supported by NSF grants DMI-9978642 and DMI-0300316.     

Role of the organic solvent modifier in the reversed phase high-performance liquid chromatography of polypeptides

Summary The retention behaviour of several polypeptide hormones on Bondapak C₁₈ columns has been examined using mobile phases of different acetonitrile percentage compositions containing 15 mM triethylammonium phosphate or 15 mM orthophosphoric acid buffers. Under these elution conditions, the capacity factors and the selectivity parameters of these polypeptide hormones show pronounced dependencies on the volume fraction of the organic solvent modifier. In the range 0–40% acetonitrile, the capacity factors were monotonously attenuated with increasing modifier percentages with the elution order essentially in accord with that hat anticipated for a reversed phase separation mode. At higher concentrations of acetonitrile, retention of the polypeptides to the octadecylsilica support progressively increased with elution order reversals indicative of a normal- or polarphase separation mode. These observations are discussed in terms of the interplay of hydrophobic and silanophilic interactions which occur between the ionised polypeptides and the stationary phase under these changing mobile phase conditions.High Performance Liquid Chromatography of Amino Acids, Peptides and Proteins, XXXII. For previous publication see ref. [1].