Hollow-fiber flow field-flow fractionation: a gentle separation method for mass spectrometry of native proteins

Low-impact ionization sources like electrospray ionization (ESI) and matrix-assisted, laser desorption/ionization (MALDI) equipped with time-of-flight (TOF) mass analyzers provide intact protein analysis over a very wide molar mass range. ESI/TOFMS provides also indications on the higher-order structure of intact proteins and non-covalent protein complexes. However, direct analysis of intact proteins mixtures in real samples shows limited success, mainly because spectra become very complex to interpret. This is also due to sample contaminants, and to the mechanism of competitive ionization in ESI or MALDI. Rapid and efficient sample clean-up and separation methods can significantly enhance the power of TOFMS for intact protein analysis. However, if protein native conditions want to be maintained, the methods should affect neither the three-dimensional structure nor the non-covalent chemistry of the proteins. Reversed-phase (RP) HPLC, size-exclusion chromatography (SEC), and capillary zone electrophoresis (CZE) are on-line or off-line coupled to ESI/TOFMS or MALDI/TOFMS. In fact, these separation methods often show limitations when applied to the analysis of native proteins. Organic modifiers and saline buffers are required in the case of RP HPLC or CZE. They can induce protein degradation or affect ionization when MS is performed after separation. High voltages used in CZE can contribute to alter proteins from their native form. In the case of high molar mass proteins, SEC is scarcely selective, and barely able to detect protein aggregates. Sample entanglement/adsorption on the stationary phase can also occur.     

Development of a supercritical fluid chromatography high-resolution separation method suitable for pharmaceuticals using cyanopropyl silica

A method has been developed for the analysis of a broad spectrum of pharmaceuticals using packed column supercritical fluid chromatography (pSFC) on a cyanopropyl silicagel stationary phase. Five 25 cm x 4.6 mm I.D., 5.0 microm columns were coupled to generate ca. 100000 plates. The selectivity was tuned by varying the nature and concentration of various modifiers and additives in the carbon dioxide mobile phase. It was noted that pressure influences both efficiency and selectivity of the chromatographic process. Final method conditions are: outlet pressure 100 bar, flow 2.0 mL/min, temperature 40 degrees C, organic modifier program from 5% (1 min) to 40% at 2.0%/min, organic modifier composition methanol:acetonitrile in a ratio of 3:1 (variable according to sample composition) with peak symmetry additives trifluoroacetic acid and diisopropylamine both at levels of 0.5%.     

A new method of high-speed cellular protein separation and insight into subcellular compartmentalization of proteins

Transglutaminase (TGM)-2 is a ubiquitous protein with important cellular functions such as regulation of cytoskeleton, cell adhesion, apoptosis, energy metabolism, and stress signaling. We identified several proteins that may interact with TGM-2 through a discovery-based proteomics method via pull down of flag-tagged TGM-2 peptide fragments. The distribution of these potential binding partners of TGM-2 was studied in subcellular fractions separated by density using novel high-speed centricollation technology. Centricollation is a compressed air-driven, low-temperature stepwise ultracentrifugation procedure where low extraction volumes can be processed in a relatively short time in non-denaturing separation conditions with high recovery yield. The fractions were characterized by immunoblots against known organelle markers. The changes in the concentrations of the binding partners were studied in cells expressing short hairpin RNA against TGM-2 (shTG). Desmin, mitochondrial intramembrane cleaving protease (PARL), protein tyrosine kinase (NTRK3), and serine protease (PRSS3) were found to be less concentrated in the 8.5%, 10%, 15%, and 20% sucrose fractions (SFs) from the lysate of shTG cells. The Golgi-associated protein (GOLGA2) was predominantly localized in 15% SF fraction, and in shTG, this shifted to predominantly in the 8.5% SF and showed larger aggregations in the cytosol of cells on immunofluorescent staining compared to control. Based on the relative concentrations of these proteins, we propose how trafficking of such proteins between cellular compartments can occur to regulate cell function. Centricollation is useful for elucidating biological function at the molecular level, especially when combined with traditional cell biology techniques.     

Matrices for capillary gel electrophoresis--a brief overview of uncommon gels

This article gives an overview of uncommon replaceable matrices (gels) for capillary gel electrophoresis. This electrophoretic technique is useful mainly for the separation and analysis of biopolymers-nucleic acids and their fragments, and proteins/peptides. Commonly used gels are not reviewed. Those mentioned and discussed here are gels containing saccharides, newly developed acrylamide-based gels and thermoadjustable viscosity polymers, namely triblock copolymers and grafted polyacrylamide.     

A new method for the radiochemical separation of rubidium and cesium

The analytical reactions of bismuth iodide and stannic chloride with cesium and rubidium are used for the radiochemical separation of these two elements. The method consists in precipitating potassium, rubidium and cesium as their cobaltinitrites, selective isolation of cesium as cesium bismuth iodide from glacial acetic acid, and subsequent separation of rubidium from potassium as chlorostannate from conc. HCl. The results obtained by the present method for the rubidium and cesium contents of the different U.S.G.S. standard rock samples are compared with those reported using methods of comparable accuracy. The suitability of the method for the analysis of fall-out samples for their radiocesium (¹³⁷Cs) contents has been demonstrated.     

Native conformational tendencies in unfolded polypeptides: development of a novel method to assess native conformational tendencies in the reduced forms of multiple disulfide-bonded proteins

Oxidative folding is the concomitant formation of the native disulfide bonds and the native tertiary structure from the reduced and unfolded polypeptide. Of interest is the inherent conformational tendency (bias) present in the reduced polypeptide to dictate the formation of the full set of native disulfide bonds. Here, by application of a novel tool, we have been able to assess this "native conformational tendency" present in reduced and unfolded bovine pancreatic ribonuclease A (RNase A). The essence of this method lies in the ability of the oxidant [Pt(en)(2)Cl(2)](2+) (where "en" is ethylenediamine) to oxidize disulfide bonds under conditions in which both reduction and disulfide reshuffling, which are essential for rearranging non-native disulfide bonds, are extremely slow. When applied to RNase A, the method revealed little or no bias toward formation of the full native set of disulfide bonds in the fully reduced protein.     

Development of native two-dimensional electrophoresis methods for the separation and detection of platinum carrying serum proteins: initial steps

The initial development steps of a native and powerful two-dimensional electrophoretic (2-D) method for the separation of platinum-proteins is described. Mild conditions were selected, particularly for the second dimension, e.g., avoiding buffer systems with platinophile N- or S-donor groups. Therefore, the separation reagents were checked if and at which concentration they can be used for this purpose. In the first dimension isoelectric focusing (IEF) was performed using immobilised pH gradients (IPGs). Native polyacrylamide gel electrophoresis (PAGE) was done in the second dimension. Detection of proteins was achieved via silverstaining. For the determination of platinum in the ultra-trace range, double focusing inductively coupled plasma mass spectrometry (HR-ICP-MS) was used. Autoradiography (¹⁹¹Pt tracer) will be done additionally in the future as a fast, powerful and elegant way of detecting the platinum carrying proteins after the second dimension.     

A new method for the radiochemical separation of copper from fission products

A new method for obtaining radiochemically pure⁶⁷Cu from highly active fission product solutions is described. The method is based on the solvent extraction of the Cu(II)-diethyldithiocarbamate complex in n-butyl acetate in the presence of hold-back carriers for Ni, Co, Mn, Mo, rare earths, Cd, Te and Sb, and subsequent purification steps involving scavengings for Ag, Ba, Sr and Fe followed by an anion-exchange purification step for decontamination from Te. Copper is finally extracted as the α-benzoin oxime complex in which form it is mounted and counted. The method has several advantages over other methods in that decontamination is very high and it is sufficiently fast considering the stringent radiochemical purity achieved. The⁶⁷Cu separated by this procedure from a one-day-old mixture of fission products arising from 10¹⁰ fissions was found to be completely free of any contamination.     

Poly(N,N-dimethylacrylamide)-grafted polyacrylamide: a self-coating copolymer for sieving separation of native proteins by CE

The potential of a series of newly synthesized poly(N,N-dimethylacrylamide) (PDMA) grafted polyacrylamide (PAM) copolymers (P(AM-PDMA)) as a replaceable separation medium for protein analysis was studied. A comparative study with and without copolymers was performed; the separation efficiency, analysis reproducibility and protein recovery proved that the P(AM-PDMA) copolymers were efficient in suppressing the adsorption of basic proteins onto the silica capillary wall. Furthermore, the size-dependent retardation of native proteins in a representative P(AM-PDMA) copolymer was demonstrated by Ferguson analysis. The results showed that the P(AM-PDMA) copolymers combine the good coating property of PDMA and the sieving property of PAM and could be applied as a sieving matrix for the analysis of native proteins.     

Electrophoretic separation method for membrane pore‐forming proteins in multilayer lipid membranes

In this paper, we report on a novel electrophoretic separation and analysis method for membrane pore‐forming proteins in multilayer lipid membranes (MLMs) in order to overcome the problems related to current separation and analysis methods of membrane proteins, and to obtain a high‐performance separation method on the basis of specific properties of the lipid membranes. We constructed MLMs, and subsequently characterized membrane pore‐forming protein behavior in MLMs. Through the use of these MLMs, we were able to successfully separate and analyze membrane pore‐forming proteins in MLMs. To the best of our knowledge, this research is the first example of membrane pore‐forming protein separation in lipid membranes. Our method can be expected to be applied for the separation and analysis of other membrane proteins including intrinsic membrane proteins and to result in high‐performance by utilizing the specific properties of lipid membranes.     

A new method for the determination of thermodynamic equilibrium constants in separation processes

A new approach to the determination of thermodynamic equilibrium constants in ion-exchange and solvent extraction processes is described. A plot of the logarithm of the distributing species activity in the aqueous phase as a function of its concentration in the non-aqueous phase has an inflection point. The ordinate of the inflection point gives directly the logarithm of the thermodynamic equilibrium constant of the reaction considered. This was made possible by finding that the ratio between n power of the free extractant molecule (or free site) activity and the activity of the distributing species-extractant complex is unity as this point.     

Liquid-phase polymer-based retention,a new method for separation and preconcentration of elements

A method based on the retention of inorganic ions by water-soluble polymeric reagents (liquid-phase polymer-based retention) in a membrane filtration cell is suggested for the separation and preconcentration of various elements. The preseparated elements remain in the aqueous solution, which is convenient for most instrumental methods of completing the analysis. The water-soluble poly(ethyleneimine) and its thiourea and methylated derivatives are shwon to be useful for retention of different inorganic ions and their separation from elements not bound to the polymer reagent.     

一种测定赤砂糖中二氧化硫的新方法

食品中二氧化硫的含量测定 ,采用的是国家标准ＧＢ5 0 0 9.34 96盐酸副玫瑰苯胺法[1 ] ,但该法在实际运用中却存在着许多不足之处 ,如ＳＯ2 的吸收剂采用的是剧毒四氯汞钠试剂 ,且该试剂配制好后需放置过夜后过滤才可使用 ;而显色剂盐酸副玫瑰苯胺溶液的配制也较为麻烦 ,需时较长 ;更为严重的是 ,该法在未扣除有色试样背景干扰的情况下 ,对有色试样采取直接取样进行分析 ,这就给测定结果带来了较大的误差 ,特别是测定诸如赤砂糖这类颜色较深的物质中ＳＯ2 含量时 ,其较深的背景严重干扰测定 ,且测定结果往往还因其取样量的不同而不同 ,这就…     

A new method for rapid characterization of the folding pathways of multidisulfide-containing proteins

Oxidative folding is a composite process that consists of both the conformational folding to the native three-dimensional structure and the regeneration of the native disulfide bonds of a protein, frequently involving over 100 disulfide intermediate species. Understanding the oxidative folding pathways of a multiple-disulfide-containing protein is a very difficult task that often requires years of devoted research due to the high complexity of the process and the very similar features of the large number of intermediates. Here we developed a method for rapidly delineating the major features of the oxidative folding pathways of a protein. The method examines the temperature dependence of the oxidative folding rate of the protein in combination with reduction pulses. Reduction pulses expose the presence of structured intermediates along the pathways. The correlation between the regeneration rate at different temperatures and the stability of the structured intermediates reveals the role that the intermediates play in determining the pathway. The method was first tested with bovine pancreatic ribonuclease A whose folding pathways were defined earlier. Then, it was explored to discern some of the major features of the folding pathways of its homologue, frog Onconase. The results suggest that the stability of the three-dimensional structure of the native protein is a major determinant of the folding rate in oxidative folding.     

A new simple preparation of -alloisoleucine suitable for large-scale manufacture

-Alloisoleucine ( -aIle) was obtained by the resolution of the epimer mixture of -isoleucine ( -Ile) and -aIle, which was formed by epimerization of -Ile, with a resolving agent such as (2S,3S)-dibenzoyltartaric acid ((2S,3S)-DBTA) or (2S,3S)-di-4-toluoyl-tartaric acid ((2S,3S)-DTTA).