Separation of proteins by high-performance anion-exchange chromatography

The chromatographic separation of four proteins, cytochrome c, alpha 1-acid glycoprotein, ovalbumin, and beta-lactoglobulin, was achieved on a 4.6 X 250-mm wide-pore polyethyleneimine (PEI)-silica gel column (5-micron particles, 330-A pore size) with essentially baseline resolution using a 20-min linear gradient from 0.025 M potassium phosphate, pH 6.80, to 0.50 M potassium phosphate, pH 6.80. The back pressure of this anion-exchange column was 1000 psi at a flow rate of 1.0 ml/min. Protein recoveries averaged over 95% and protein capacity exceeded 33 mg for a single protein. Isocratic elution (0.040 M potassium phosphate, pH 6.8; flow rate, 0.50 ml/min) of ovalbumin gave a column efficiency of 15,700 plates/m with a peak asymmetry factor of 1.27. Resolution of these same four proteins on a 4.6 X 50-mm PEI-silica gel column occurred within 2 min. Nucleoside monophosphates were separated on the short PEI-silica column within 1 min with 0.01 M potassium phosphate, pH 2.58, at a flow rate of 6 ml/min which generated a column back pressure of 2000 psi.     

Reversible immobilization of cephalosporin C acylase on epoxy supports coated with polyethyleneimine

In this study, a recombinant cephalosporin C acylase (CCA) was covalently or physically immobilized on an epoxy-activated support LX1000-EPC4 (EP) or its derivatives, EP-polyethyleneimine (EP-PEI) and EP-ethylenediamine (EP-EDA) with cationic groups on the surface. Zeta potential was used as a tool for activated carrier analysis and immobilization analysis. The EP-PEI (the cationic polymer PEI grafted support) showed higher zeta potential than EP-EDA (the small diamine EDA modified support) and EP support. Among these three supports, immobilization of CCA on EP-PEI had the highest specific activity according to the range of enzyme loadings. Michaelis constant K_m values of EP-PEI-CCA and EP-EDA-CCA were 22?mM and 30?mM, respectively, which were lower than that of the free enzyme (43?mM), suggesting that the support’s zeta potential is related to the affinity of the enzyme for the substrate. The enzyme immobilized on EP-PEI showed a much higher thermal stability (stabilization factor of 32-fold compared with the free enzyme) than that on the EP-EDA (stabilization factor of 5.5-fold) and EP supports (stabilization factor of 1.7-fold). The adsorption of CCA on EP-PEI support was very strong and reversible. The CCA could be thoroughly desorbed using a high concentration of NaCl (e.g., 2 M) at low pH value (pH 3.0). The regenerated EP-PEI support could then be reused for enzyme immobilization.     

RNA interference-mediated simultaneous silencing of four genes using cross-shaped RNA

The structural flexibility of RNA interference (RNAi)-triggering nucleic acids suggests that the design of unconventional RNAi trigger structures with novel features is possible. Here, we report a cross-shaped RNA duplex structure, termed quadruple interfering RNA (qiRNA), with multiple target gene silencing activity. qiRNA triggers the simultaneous down-regulation of four cellular target genes via an RNAi mechanism. In addition, qiRNA shows enhanced intracellular delivery and target gene silencing over conventional siRNA when complexed with jetPEI, a linear polyethyleneimine (PEI). We also show that the long antisense strand of qiRNA is incorporated intact into an RNA-induced silencing complex (RISC). This novel RNA scaffold further expands the repertoire of RNAi-triggering molecular structures and could be used in the development of therapeutics for various diseases including viral infections and cancer.     

Recent advances in bioprocessing application of membrane chromatography

Compared to traditional chromatography using resins in packed-bed columns, membrane chromatography is a relatively new and immature bioseparation technology based on the integration of membrane filtration and liquid chromatography into a single-stage operation. Over the past decades, advances in membrane chemistry have yielded novel membrane devices with high binding capacities and improved mass transfer properties, significantly increasing the bioprocessing efficiency for purification of biomolecules. Due to the disposable nature, low buffer consumption, and reduced equipment costs, membrane chromatography can significantly reduce downstream bioprocessing costs. In this review, we discuss technological merits and disadvantages associated with membrane chromatography as well as recent bioseparation applications with a particular attention on purification of large biomolecules.     

以软刻技术微图案化培养纹状体神经元的形态学研究

探讨以软刻技术微加工带正电荷的聚乙烯亚胺(polyethyleneimine, PEI)图案,对培养纹状体神经元黏附存活及突起生长的影响．以软刻技术(微接触印刷方法)微加工三种不同的黏附底物：层粘连蛋白(laminin, LN)、带正电荷的多聚赖氨酸(poly-L-lysine, PLL)和PEI．新生乳鼠纹状体神经元体外分离培养,观察不同黏附底物对纹状体神经元黏附、存活和突起生长状态的影响,观察神经元在不同黏附底物上形成网络图案的差异．结果表明,在PEI 和PLL表面生长的神经元数量明显大于LN组,PEI与PLL、LN相比能形成更为完整的神经元图案．带强正电荷的PEI有助于神经元在其表面形成相对完整的图案,是构建体外神经网络的一种良好界面材料．     

Interaction of polyethyleneimine‐anchored copper(II) complexes with tRNA studied by spectroscopy methods and biological activities

Ultraviolet–visible, emission and circular dichroism spectroscopic methods were used in transfer RNA (tRNA) interaction studies performed for polyethyleneimine–copper(II) complexes [Cu(phen)(l ‐Tyr)BPEI]ClO₄ (where phen =1,10‐phenanthroline, l ‐Tyr = l ‐tyrosine and BPEI = branched polyethyleneimine) with various degrees of coordination (x = 0.059, 0.149, 0.182) in the polymer chain. The results indicated that polyethyleneimine–copper(II) complexes bind with tRNA mostly through surface binding, although other binding modes, such as hydrogen bonding and van der Waals interactions, might also be present. Dye‐exclusion, sulforhodamine B and 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assays of a polyethyleneimine–copper(II) complex with a higher degree of coordination against different cancer cell lines proved that the complex exhibited cytotoxic specificity and a significant cancer cell inhibition rate. Antimicrobial screening showed activity against some human pathogens.