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  • 1
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    A novel iron uptake mechanism mediated by GPI-anchored human p97. (1995)
    EMBO Press
    Details
    Publication Date: 1995-09-01
    Print ISSN: 0261-4189
    Electronic ISSN: 1460-2075
    Topics: Biology , Medicine
    Published by EMBO Press on behalf of European Molecular Biology Organization.
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Controlled release process to recover heterologous glycosylphosphatidylinositol membrane anchored proteins from CHO cells (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 480-486 
    Details
    ISSN: 0006-3592
    Keywords: CHO ; PI-PLC ; heterologous glipiated proteins ; controlled release ; GPI anchor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A semicontinuous process has been developed to recover heterologous proteins at increased concentrations and purities. Proteins attached to mammalian cell membranes by glycosylphosphatidylinositol (GPI) anchors can be selectively released into the supernatant by the enzyme phosphatidylinositol-phospholipase C (PI-PLC). Chinese hamster ovary (CHO) cells, genetically engineered to express the GPI anchored, human melanoma antigen (p97), were used as a model system. These cells were grown in protein containing growth medium. During a brief harvesting phase the medium was replaced by phosphate buffered saline (PBS) containing 10 mU/mL of PI-PLC and the GPI anchored protein was cleaved from the cell surface and recovered in soluble form at up to 30% purity. After harvesting, the cells were returned to growth medium where the protein was re-expressed within 40 h. The growth rate, viability, and protein production of cells, repeatedly harvested over a 44-day period, were not adversely affected. This continuous cyclic harvesting process allowed recovery of a heterologous protein at high purity and concentrations and could be applied to the recovery of other GPI anchored proteins and genetically engineered GPI anchored fusion proteins. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260420411
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  • 3
    Electronic Resource
    Electronic Resource
    Membrane anchored protein production from spheroid, porous, and solid microcarrier chinese hamster ovary cell cultures (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 47 (1995), S. 550-556 
    Details
    ISSN: 0006-3592
    Keywords: spheroids ; porous and solid microcarriers ; CHO ; controlled release ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of the microcarrier type on the performance of a controlled release process used to produce a recombinant glycosyl-phosphatidylinositol anchored protein was investigated. Chinese hamster ovary (CHO) cells expressing the human melanoma tumor antigen (p97) were cultured in 10% serum on Cultispher-GH porous microcarriers and then, for protein production, maintained in 2% serum. Cells were harvested every 48 h and p97 was recovered at 90 μg/mL and 40% purity. Harvested p97 concentrations were increased by harvestingfrom spheroid (241 μg/mL) and smaller porous microcarrier, Cultispher-G (167 μg/mL) cultures. The low total cell specific p97 production of cells cultured on Cultispher-GH was due to necrosis of cells within the beads, decreased p97 expression of the immobilized cells, dilution by the liquid (up to 40% volume) associated with settled beads, and incomplete recovery of p97 from within the beads. Cells cultured on solid microcarriers, Cytodex-1, had the highest cell viability and cell specific p97 production, It is recommended that a two-stage cyclic harvesting process of cells cultured on small Cultispher-G or on Cytodex-1 beads would minimize protein loss and maximize cell specific protein recovery. © 1995 John Wiley & Sons Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260470507
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  • 4
    Electronic Resource
    Electronic Resource
    Increasing GPI-anchored protein harvest concentrations from suspension and porous microcarrier CHO cell cultures (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 136-147 
    Details
    ISSN: 0006-3592
    Keywords: CHO cells ; glycosyl-phosphatidylinositol p97 concentration ; protein harvest ; controlled release ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chinese hamster ovary (CHO) cells expressing the human melanoma tumour antigen, p97, were used to develop a controlled release process for the production of recombinant glycosyl-phosphatidylinositol (GPI) anchored proteins. The cells were cultured either in suspension or immobilized on porous microcarriers and p97 was selectively cleaved from the cell surface by the bacterial enzyme, phosphatidylinositol-phospholipase C (PI-PLC). The kinetics of p97 cleavage from the cell surface by PI-PLC was shown to be approximated by Michaelis-Menten kinetics. The recovered p97 concentrations were increased by reusing the PI-PLC enzyme solution to harvest multiple batches of cells. A convenient PI-PLC assay was developed to monitor the harvesting process and to determine the stability of PI-PLC under harvesting conditions. Although the Pl-PLC was stable under harvesting conditions, it rapidly adsorbed to the cell surface and was depleted from the reused enzyme solution. In order to maintain PI-PLC activity, it was necessary to add fresh PI-PLC to the reused enzyme solution before harvesting a fresh batch of cells. The maximum p97 concentration that could be obtained from harvesting CHO cells cultured on porous microcarriers was limited by the dilution effects of sample removal, adding fresh PI-PLC and liquid associated with settled microcarriers. A model was developed that adequately predicted the p97 concentration after each harvest and the maximum p97 concentration that could be achieved by this harvesting method. The dilution effects were minimized by harvesting from centrifuged suspension culture cells and the harvested p97 concentration was increased by over sixfold to 0.64 mg/mL. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 136-147, 1997.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Expression of cell surface GPI-anchored human p97 in baculovirus-infected insect cells (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 41-53 
    Details
    ISSN: 0006-3592
    Keywords: baculovirus ; insect cell ; p97 ; glycosylation ; GPI anchor ; protein expression ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The baculovirus/insect cell system (Autographa californica multiple nuclear polyhedrosis virus/Spodoptera frugiperda Sf9 cells) was used to express the GPI-anchored human melanoma tumor antigen, melanotransferrin or p97. This system served to study the expression and productivity of recombinant GPI-anchored p97 by insect cells. The Sf9 cells expressed a cell surface GPI-anchored form of p97 as well as a soluble form of p97 that did not appear to be derived from the GPI-anchored form of p97. Both recombinant forms, although Endo H resistant, migrated slightly faster (∼88 kDa) than the native p97 (∼95-97 kDa). The insect GPI-anchored p97 was sensitive to PI-PLC, which exposed a detectable cross-reacting determinant. The Sf9 cell surface p97 expression was similar to that of human melanoma (SK-MEL-28) cells, whereas the Sf9 cell specific secretion rate was 10-fold higher. Also Sf9 cells retained considerably higher levels of p97 within the cell. The Sf9 cell surface expression of p97 varied with time after infection, with the maximum expression, which appeared independent of multiplicities of infection greater than 1, occurring at 48 h. After 48 h, levels of cell surface and secreted p97 fell whereas p97 retained within the cell increased, which possibly reflected the lytic nature of the expression system. The successful expression of GPI-anchored human p97 by the baculovirus/insect cell system not only provides a source of p97 for further research but also is the basis of an alternative method for the commercial production of GPI-anchored proteins. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 41-53, 1997.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Glycolipid membrane anchored recombinant protein production from CHO cells cultGred on porous microcarriers (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 45-54 
    Details
    ISSN: 0006-3592
    Keywords: microcarriers, porous ; melanotransferrin human ; CHO cells ; protein production ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recombinant proteins were harvested from Chinese hamster ovary (CHO) cells by a controlled release process, which increased the purity and concentration of the harvested protein. Recombinant human melano-transferrin (p97) was expressed linked to the outer surface of CHO cells by a glycosyl-phosphatidylinositol (GPI) membrane anchor. Cells were grown to confluence in T-flask culture, and the p97 harvested by replacing the growth medium for 30 min with phosphate-buffered saline (PBS) containing 10 mU/mL phosphatidylinositol-phospholipase C (PI-PLC). The GPI anchor was selectively cleaved by PI-PLC. In fresh medium, the CHO cells regained over 95% of their p97 expression within 40 h. The process was repeated for eight harvests. Harvested protein concentrations varied from 1.5 to 3.8 μg/mL due to difficulties in maintaining stable confluent T-flask cultures. Harvesting from cells growing on porous microcarriers was investigated to increase p97 product concentrations and to overcome culture stability problems. Semicontinuous cultures were maintained in spinners for up to 76 days with average bioreactor cell densities of over 107 cell/mL. The p97 was harvested at up to 100 μg/mL and 30% purity with protein production remaining stable for 4 harvest cycles. Production of high levels of p97 from CHO cells was maintained at 0.5% serum. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260440108
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