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Stefanik O, Majerova P, Kovac A, Mikus P, Piestansky J. Capillary electrophoresis in the analysis of therapeutic peptides-A review. Electrophoresis 2024; 45:120-164. [PMID: 37705480 DOI: 10.1002/elps.202300141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 08/10/2023] [Accepted: 08/14/2023] [Indexed: 09/15/2023]
Abstract
Therapeutic peptides are a growing class of innovative drugs with high efficiency and a low risk of adverse effects. These biomolecules fall within the molecular mass range between that of small molecules and proteins. However, their inherent instability and potential for degradation underscore the importance of reliable and effective analytical methods for pharmaceutical quality control, therapeutic drug monitoring, and compliance testing. Liquid chromatography-mass spectrometry (LC-MS) has long time been the "gold standard" conventional method for peptide analysis, but capillary electrophoresis (CE) is increasingly being recognized as a complementary and, in some cases, superior, highly efficient, green, and cost-effective alternative technique. CE can separate peptides composed of different amino acids owing to differences in their net charge and size, determining their migration behavior in an electric field. This review provides a comprehensive overview of therapeutic peptides that have been used in the clinical environment for the last 25 years. It describes the properties, classification, current trends in development, and clinical use of therapeutic peptides. From the analytical point of view, it discusses the challenges associated with the analysis of therapeutic peptides in pharmaceutical and biological matrices, as well as the evaluation of CE as a whole and the comparison with LC methods. The article also highlights the use of microchip electrophoresis, nonaqueous CE, and nonconventional hydrodynamically closed CE systems and their applications. Overall, the article emphasizes the importance of developing new CE-based analytical methods to ensure the high quality, safety, and efficacy of therapeutic peptides in clinical practice.
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Affiliation(s)
- Ondrej Stefanik
- Department of Pharmaceutical Analysis and Nuclear Pharmacy, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
- Toxicological and Antidoping Center, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
| | - Petra Majerova
- Institute of Neuroimmunology, Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Andrej Kovac
- Institute of Neuroimmunology, Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Peter Mikus
- Department of Pharmaceutical Analysis and Nuclear Pharmacy, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
- Toxicological and Antidoping Center, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
| | - Juraj Piestansky
- Toxicological and Antidoping Center, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
- Institute of Neuroimmunology, Slovak Academy of Sciences, Bratislava, Slovak Republic
- Department of Galenic Pharmacy, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovak Republic
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Abstract
Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.
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Affiliation(s)
- Ashwin Ramachandran
- Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305, United States
| | - Juan G Santiago
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
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Reciprocating free-flow isoelectric focusing with online array ultraviolet detector for process monitoring of protein separation. J Chromatogr A 2022; 1663:462747. [PMID: 34973480 DOI: 10.1016/j.chroma.2021.462747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/06/2021] [Accepted: 12/11/2021] [Indexed: 11/22/2022]
Abstract
Free-flow isoelectric focusing (FFIEF) is a useful tool for separating and purifying proteins, DNA, cells, and organelles, etc. However, the online monitoring of each fraction during an FFIEF run has not been achieved yet, resulting in a lack of process monitoring of FFIEF. Herein, an online array ultraviolet (UV) detection system was developed for the easy assay of FFE fractions. The detector was integrated with an apparatus of FFIEF with 32 fractions to show the online monitoring, and bovine serum albumin (BSA) and lysozyme were chosen as the model proteins for manifesting the UV detector performance. The experiments revealed that (i) all the fluidic cells had good linearity from 0.03 to 10 mg/mL BSA and fair limits of detection (LODs) of 0.01 mg/mL; (ii) all the cells had good uniformity of UV absorbance; and (iii) the deviations of intra-day and inter-day of UV detector were respectively 3.8% and 5.8%, indicating the fair stability of the UV detector. The UV detector could be well used for the process monitoring of two model proteins through the whole FFIEF run, and the online absorbance assay of proteins at the end of FFIEF. The UV detector herein had the evident potential for rapid and convenient assay of protein fraction in FFIEF as well as other FFE modes.
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Thomas SL, Thacker JB, Schug KA, Maráková K. Sample preparation and fractionation techniques for intact proteins for mass spectrometric analysis. J Sep Sci 2020; 44:211-246. [DOI: 10.1002/jssc.202000936] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 10/28/2020] [Accepted: 10/29/2020] [Indexed: 12/17/2022]
Affiliation(s)
- Shannon L. Thomas
- Department of Chemistry & Biochemistry The University of Texas Arlington Arlington Texas USA
| | - Jonathan B. Thacker
- Department of Chemistry & Biochemistry The University of Texas Arlington Arlington Texas USA
| | - Kevin A. Schug
- Department of Chemistry & Biochemistry The University of Texas Arlington Arlington Texas USA
| | - Katarína Maráková
- Department of Pharmaceutical Analysis and Nuclear Pharmacy Faculty of Pharmacy Comenius University in Bratislava Bratislava Slovakia
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Yang Y, Kong FZ, Liu J, Li JM, Liu XP, Li GQ, Wang JF, Xiao H, Fan LY, Cao CX, Li S. Enhancing resolution of free-flow zone electrophoresis via a simple sheath-flow sample injection. Electrophoresis 2016; 37:1992-7. [DOI: 10.1002/elps.201600002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 04/01/2016] [Accepted: 04/05/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Ying Yang
- School of Bioscience and Bioengineering; South China University of Technology; Guangzhou P. R. China
| | - Fan-Zhi Kong
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Ji Liu
- School of Bioscience and Bioengineering; South China University of Technology; Guangzhou P. R. China
| | - Jun-Min Li
- School of Bioscience and Bioengineering; South China University of Technology; Guangzhou P. R. China
| | - Xiao-Ping Liu
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Guo-Qing Li
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Ju-Fang Wang
- School of Bioscience and Bioengineering; South China University of Technology; Guangzhou P. R. China
| | - Hua Xiao
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Liu-Yin Fan
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Cheng-Xi Cao
- Laboratory of Analytical Biochemistry and Bioseparation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Shan Li
- School of Bioscience and Bioengineering; South China University of Technology; Guangzhou P. R. China
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Kondeková M, Staňová A, Marák J. Methodological aspects of an off-line combination of preparative isotachophoresis and high-performance liquid chromatography with mass spectrometry in the analysis of biological matrices. Electrophoresis 2014; 35:1173-80. [DOI: 10.1002/elps.201300485] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 01/09/2014] [Accepted: 01/09/2014] [Indexed: 11/11/2022]
Affiliation(s)
- Monika Kondeková
- Department of Analytical Chemistry; Faculty of Natural Sciences; Comenius University in Bratislava; Bratislava Slovak Republic
| | - Andrea Staňová
- Department of Analytical Chemistry; Faculty of Natural Sciences; Comenius University in Bratislava; Bratislava Slovak Republic
| | - Jozef Marák
- Department of Analytical Chemistry; Faculty of Natural Sciences; Comenius University in Bratislava; Bratislava Slovak Republic
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7
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Purification of nucleic acids using isotachophoresis. J Chromatogr A 2014; 1335:105-20. [DOI: 10.1016/j.chroma.2013.12.027] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 12/04/2013] [Accepted: 12/07/2013] [Indexed: 12/30/2022]
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9
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Shkolnikov V, Bahga SS, Santiago JG. Desalination and hydrogen, chlorine, and sodium hydroxide production via electrophoretic ion exchange and precipitation. Phys Chem Chem Phys 2012; 14:11534-45. [DOI: 10.1039/c2cp42121f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Marák J, Staňová A, Gajdoštínová S, Škultéty L, Kaniansky D. Some possibilities of an analysis of complex samples by a mass spectrometry with a sample pretreatment by an offline coupled preparative capillary isotachophoresis. Electrophoresis 2011; 32:1273-81. [DOI: 10.1002/elps.201000629] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Revised: 01/10/2011] [Accepted: 01/20/2011] [Indexed: 01/30/2023]
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Ranc V, Staňová A, Marák J, Maier V, Ševčík J, Kaniansky D. Preparative isotachophoresis with surface enhanced Raman scattering as a promising tool for clinical samples analysis. J Chromatogr A 2011; 1218:205-10. [DOI: 10.1016/j.chroma.2010.11.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 10/29/2010] [Accepted: 11/15/2010] [Indexed: 11/26/2022]
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Islinger M, Eckerskorn C, Völkl A. Free-flow electrophoresis in the proteomic era: A technique in flux. Electrophoresis 2010; 31:1754-63. [DOI: 10.1002/elps.200900771] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Stone VN, Baldock SJ, Croasdell LA, Dillon LA, Fielden PR, Goddard NJ, Thomas CLP, Treves Brown BJ. Free flow isotachophoresis in an injection moulded miniaturised separation chamber with integrated electrodes. J Chromatogr A 2006; 1155:199-205. [PMID: 17229431 DOI: 10.1016/j.chroma.2006.12.031] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2006] [Revised: 11/28/2006] [Accepted: 12/01/2006] [Indexed: 11/24/2022]
Abstract
An injection moulded free flow isotachophoresis (FFITP) microdevice with integrated carbon fibre loaded electrodes with a separation chamber of 36.4mm wide, 28.7 mm long and 100 microm deep is presented. The microdevice was completely fabricated by injection moulding in carbon fibre loaded polystyrene for the electrodes and crystal polystyrene for the remainder of the chip and was bonded together using ultrasonic welding. Two injection moulded electrode designs were compared, one with the electrode surface level with the separation chamber and one with a recessed electrode. Separations of two anionic dyes, 0.2mM each of amaranth and acid green and separations of 0.2mM each of amaranth, bromophenol blue and glutamate were performed on the microdevice. Flow rates of 1.25 ml min(-1) for the leading and terminating electrolytes were used and a flow rate of 0.63 ml min(-1) for the sample. Electric fields of up to 370 V cm(-1) were applied across the separation chamber. Joule heating was not found to be significant although out-gassing was observed at drive currents greater than 3 mA.
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Affiliation(s)
- Victoria N Stone
- School of Chemical Engineering and Analytical Science, The University of Manchester, PO Box 88, Manchester M60 1QD, UK
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Madajová V, Simunicová E, Kaniansky D, Marák J, Zelenská V. Fractionation of glycoforms of recombinant human erythropoietin by preparative capillary isotachophoresis. Electrophoresis 2005; 26:2664-73. [PMID: 15929059 DOI: 10.1002/elps.200500044] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This feasibility study deals with the use of preparative capillary isotachophoresis (CITP), operating in a discontinuous fractionation mode, to the separations and isolations of glycoforms of recombinant human erythropoietin (rhEPO). The preparative CITP separations were monitored by capillary zone electrophoresis (CZE) with a hydrodynamically closed separation unit. Such a CZE system, suppressing fluctuations of the migration data linked with fluctuations of EOF and hydrodynamic flow, made possible to evaluate and compare the preparative CITP separations performed within a longer time frame. Preparative CITP, carried out in the separation unit with coupled columns of enhanced sample loadability, separating 100 microg of rhEPO in a run lasting ca. 30 min, gave the production rate higher than 55 ng/s for the rhEPO glycoforms. The preparative separations included valve isolations of the glycoforms from the ITP stack into four or six fractions. Such numbers of the fractions corresponded to typical numbers of the major glycoform peaks as resolved in CZE of rhEPO. With respect to close effective mobilities of the glycoforms and a multicomponent nature of rhEPO, the fractions contained mixtures of glycoforms with the dominant glycoforms enriched 10-100-fold, relative to the original rhEPO sample.
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Affiliation(s)
- Vlasta Madajová
- Department of Analytical Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
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Marák J, Nagyová I, Kaniansky D. Computer-assisted choice of discrete spacers for anionic isotachophoresis separations. J Chromatogr A 2003; 1018:233-49. [PMID: 14620574 DOI: 10.1016/j.chroma.2003.08.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In isotachophoresis (ITP), the sample constituents migrate, depending on their concentrations in the loaded sample, either in fully developed zones or in the boundary layers between the zones of constituents of the corresponding effective mobilities. The latter (spike) migration mode is analytically beneficial in selective detections of trace analytes, especially, when appropriately chosen discrete spacers minimize detection interferences due to matrix constituents. To facilitate a search for suitable mixtures of discrete spacers, a two-step calculation procedure was developed in this work. Using a pool of discrete spacers consisting of 42 anionic and zwitterionic constituents, this procedure was shown effective in the anionic ITP separations performed at pH = 6.5-10.0. Besides the predictions of the migration orders, it was helpful in identifying the spacing constituents that could cause resolution problems due to an uncertainty with which pH of the leading electrolyte solution is known. The ionic mobility and pKa data, taken for the spacing constituents from the literature and the ones obtained from the ITP experiments carried out in this work, were used in the calculations performed in a context with the choice of spacers. Although the data obtained from the ITP experiments provided better results, small uncertainties with which they were acquired (attributable to fluctuations in the experimental conditions) set practical limits in the calculation based choice of multi-component mixtures of the spacing constituents.
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Affiliation(s)
- Jozef Marák
- Department of Analytical Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská Dolina CH-2, SK-842 15 Bratislava, Slovak Republic
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Abstract
The use of capillary isotachophoresis (ITP), operating in a discontinuous fractionation mode, for preparative separations of enantiomers of chiral compounds was studied. The ITP separations were carried out in the column-coupling configuration of the separation unit provided with the preseparation column of a 1.0 mm ID and the trapping column of a 0.8 mm ID. Such a configuration of the CE separation unit offers several working regimes suitable to preparative separations of enantiomers. 2,4-Dinitrophenyl-DL-norleucine (DNP-Norleu) was employed as a model analyte in our experiments with beta-cyclodextrin serving in the electrolyte solutions as a chiral selector. The preparative separations lasting about 20 min were evaluated by ITP and (more often) by capillary zone electrophoresis (CZE). It was found that one preparative run provided up to 14 microg of pure DNP-Norleu enantiomers. This corresponded to a 75 times higher production rate of ITP relative to a maximum value of this parameter as estimated for preparative CZE runs in cylindrical capillaries (0.5 pmol/s). About 75% of the DNP-Norleu enantiomers loaded into the preparative equipment could be recovered in pure enantiomer fractions. Contiguous natures of the zones in the ITP stack and adsorption losses of the enantiomers in the isolation step were found to set practical limits for a further enhancement of the recovery rates in the isolation of pure enantiomers.
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Affiliation(s)
- D Kaniansky
- Department of Analytical Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic.
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Church MN, Spear JD, Russo RE, Klunder GL, Grant PM, Andresen BD. Transient Isotachophoretic−Electrophoretic Separations of Lanthanides with Indirect Laser-Induced Fluorescence Detection. Anal Chem 1998; 70:2475-80. [DOI: 10.1021/ac971043+] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
This review evaluates the literature on continuous free flow electrophoresis, published during the last four years. Its aim is to serve not only experts in the field but also newcomers, and, therefore, it also briefly describes the principles of the method and the techniques used, referring to fundamental papers published earlier. The actual commercial instrumentation is briefly outlined. A substantial part of this review is devoted to the optimization of the performance of this method. Finally, diverse applications of fractionations of charged species in solution, ranging from small ions to biological particles and cells, are surveyed.
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Affiliation(s)
- L Krivánková
- Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Brno
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Abstract
Capillary isotachophoresis is a powerful electromigration separation method with a pronounced capability to concentrate trace components in diluted samples. At present, capillary isotachophoresis is utilized predominantly as the first step in on-line combination with capillary zone electrophoresis. This article is a continuation of previous reviews and summarizes the results published during 1993-1996.
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Affiliation(s)
- P Gebauer
- Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Brno
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Wroński M. Fingerprint of anions involving pKa, mobility and concentration established by using capillary isotachophoresis. J Chromatogr A 1997. [DOI: 10.1016/s0021-9673(97)00141-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Hutta M, Kaniansky D, Kovalčíková E, Marák J, Chalányová M, Madajová V, Šimuničová E. Preparative capillary isotachophoresis as a sample pretreatment technique for complex ionic matrices in high-performance liquid chromatography. J Chromatogr A 1995. [DOI: 10.1016/0021-9673(94)00854-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Weber W, Wenisch E, Günther N, Marnitz U, Betzel C, Righetti PG. Protein microheterogeneity and crystal habits: the case of epidermal growth factor receptor isoforms as isolated in a multicompartment electrolyzer with isoelectric membranes. J Chromatogr A 1994; 679:181-9. [PMID: 7951989 DOI: 10.1016/0021-9673(94)80325-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A purified, soluble form of the epidermal growth factor receptor (sEGFR) was found, by isoelectric focusing in immobilized pH gradients, to consist of three major isoforms (with pI values 6.45, 6.71 and 6.96, respectively) and ca. a dozen minor components. This wild-type sEGFR, while producing crystals, has so far defied any attempt at decoding the structure, due to the very poor diffraction pattern. When the wild-type sEGFR was purified in a multicompartment electrolyzer with isoelectric Immobiline membranes, it yielded the three major isoforms as single-pI components, collected in three separate chambers of the recycling electrolyzer. The pI 6.71 and the pI 6.96 isoforms produced large crystals of apparent good quality. However, while the former produced a high-quality diffraction pattern, which may lead to decoding of three-dimensional structure, the pI 6.96 produced crystals which did not diffract at all. It is concluded that, in the case of "tough" proteins (large size, heterogeneous glycosylation, high water content of crystals), purification to single-charge components might be an essential step for growing proper crystals. The unique advantage of purification via isoelectric membranes is that the protein is collected both isoelectric and isoionic, i.e. uncontaminated by soluble buffers (such as the carrier ampholytes used in conventional focusing).
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Affiliation(s)
- W Weber
- Institut für Physiologische Chemie, Universitätskrankenhaus Eppendorf, Hamburg, Germany
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