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- Xiao, Jin-Xin, et al.
(författare)
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Phase behavior and protein partitioning in aqueous two-phase systems of cationic-anionic surfactant mixtures
- 2000
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Ingår i: Journal of Chromatography. B. - 1387-2273. ; 743:1-2, s. 327-338
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Tidskriftsartikel (refereegranskat)abstract
- Cationic-anionic surfactant mixtures can form aqueous two-phase systems. Such aqueous surfactant two-phase systems (ASTP systems) can be used for separation and purification of biomaterials. In this work we investigated the phase behavior and the partitioning of BSA and lysozyme in the ASTP system formed by mixtures of dodecyltriethylammonium bromide and sodium dodecylsulfate (SDS). The pseudo ternary phase diagram of these mixtures at low total surfactant concentrations contains two narrow two-phase regions, which represent two kinds of different ASTP systems formed when cationic and anionic surfactants are in excess, respectively (called ASTP-C and ASTP-A). The phase separation is associative, one phase is surfactant-rich, and the other phase is surfactant-depleted. Mechanisms behind the phase behavior are discussed. The phase behavior, especially phase separation time and phase volume ratio, is strongly influenced by total concentration and molar ratio of mixed surfactants. The effect of molar ratio is strong, which enables one to get desired phase systems also at very low total concentration by tuning the molar ratio of the surfactants. It was shown that the marked differences of surfactant concentration between the phases makes proteins distribute with different partitioning coefficients. The charges on the micellar surface, which can be adjusted by tuning the molar ratio of cationic surfactants to anionic surfactants, enhance the selectivity of protein partitioning by electrostatic effects. At pH 7.1, in the ASTP-C systems, negatively charged BSA is concentrated in the surfactant-rich phase and positively charged lysozyme in the surfactant-depleted phase, while in ASTP-A systems, a totally opposite partitioning was observed. It was shown that lysozyme could retain activity in ASTP systems.
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| 2. |
- Xin, Sun, et al.
(författare)
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A novel protein localized to the fibrillar compartment of the nucleolus and to the brush border of a secretory cell
- 2002
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Ingår i: European Journal of Cell Biology. - : Elsevier BV. - 0171-9335 .- 1618-1298. ; 81:3, s. 125-137
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Tidskriftsartikel (refereegranskat)abstract
- We report the identification and molecular characterization of a novel abundant nucleolar protein of the dipteran Chironomus tentans. As shown by Western blot analysis, this protein is present in nuclear extracts in a phosphorylated form with a mobility corresponding to 100 kDa. Therefore, the protein has been termed Chironomus tentans p100, or p100 for short. Analysis of the cDNA-derived primary structure of p100 indicates a protein that contains a combination of structural domains which could be involved in interactions with proteins and nucleic acids: twelve alternating acidic and basic repeats, a glycine-arginine-rich domain and a region with two zinc fingers of the C4-type. Acidic and basic repeats are typical for a group of nonribosomal nucleolar proteins. The best-studied representatives of this group are Nopp140 and nucleolin, proteins with structural and regulatory functions in rDNA transcription. Immunocytology and immunoelectron microscopy of Chironomus tentans salivary gland cells have shown that the p100 protein is located in the fibrillar compartment of the nucleolus, while it is almost absent from the granular compartment and from the nucleoplasm. The p100 protein remains in the nucleolus after removal of RNA and DNA by digestion with nucleases. This indicates that p100 might be a constituent of the nucleolar proteinaceous framework. Remarkably, p100 is also localized in the brush border in the apical part of the salivary gland cell. The presence of p100 both in the nucleolus and at the apical plasma membrane suggests that it could be involved in coordination of the level of protein production and export from the cell through regulation of the level of rRNA production in the nucleolus.
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