@article{StopperZimmermannWecker1985,
  author    = {Stopper, Helga and Zimmermann, U. and Wecker, E.},
  title     = {High yields of DNA-transfer into mouse L-cells by electropermeabilization},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82408},
  year      = {1985},
  abstract  = {no abstracts available},
  subject      = {Toxikologie},
  language  = {en}
}
@article{ZimmermannStopper1986,
  author    = {Zimmermann, U. and Stopper, Helga},
  title     = {Elektrofusion und Elektropermeabilisierung von Zellen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86865},
  year      = {1986},
  abstract  = {No abstract available.},
  subject      = {Elektrofusion},
  language  = {de}
}
@article{StopperJonesZimmermann1987,
  author    = {Stopper, Helga and Jones, H. and Zimmermann, U.},
  title     = {Large scale transfection of mouse L-cells by electropermeabilization},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63497},
  year      = {1987},
  abstract  = {Mouse L-cells were transfected by electropenneabilization using the selectable plasmid pSV2-neo which confers resistance to G-418 (Geneticin). 1be DNA concentration used was 1 l'gfml, the field strength was 10 kV fcm, the duration of the pulse was S ~s. Transfeetion yield was optimal at a temperature of 4°C when using a time in between consecutive pulses of 1 minute compared to shorter (of the order of seoonds) or Ionger (3 minutes) time intervals. A more detailed study of the relationship between the number of pulses applied (up to 10) and transfection yield showed it to be almost linear in this range at 4 o C. The yield of transfectants in response to 10 pulses was up to 1000 per 106 cells (using 3.3 pg DNA per cell). The inßuence of the growth phase of the cells on the transfection yield and I or the subpopulation of the mouse L--ceU line used was shown. Furthennore the clone yield depended on the DNA per ceU ratio within a very small range.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{HollerFischerWeberetal.1987,
  author    = {Holler, E. and Fischer, H. and Weber, C. and Stopper, Helga and Steger, H. and Simek, H.},
  title     = {A DNA polymerase with unusual properties from the slime mold Physarum polycephalum},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63501},
  year      = {1987},
  abstract  = {Two forms of a DNA polymerase have been purified from microplasmodia of Physarum polycephalum by poly(ethyleneimine) precipitation and chromatography on DEAE-Sephacel, phosphocellulose, heparin Sepharose, hydroxyapatite, DNA-agarose, blue-Sepharose. They were separated from DNA polymerase cx on phosphocellulose and from each other on heparin-Sepharose. Form HS1 enzymewas 30-40\% pure and form HS2 enzyme 60\% with regard toprotein contents of the preparations. Form HS2 enzymewas generated from form HS1 enzyme on prolonged standing of enzyme preparations. The DNA polymerases were obtained as complexes of a 60-kDa protein associated with either a 135-kDa (HS1) or a 110-kDa (HS2) DNA-polymerizing polypeptidein a 1:1 molar stoichiometry. The biochemical function of the 60-kDa protein remained unknown. The complexes tended to dissociate during gradient centrifugation and during partition chromatography as weil as during polyacrylamide gradient gel electrophoresis under nondenaturing conditions at high dilutions of samples. Both forms existed in plasmodia extracts, their proportions depending on several factors including those which promoted proteolysis. The DNA polymerases resembled eucaryotic DNA polymerase ß by several criteria and were functionally indistinguishable from each other. It is suggested that lower eucaryotes contain repair DNA polymerases, which are similar to those of eubacteria on a molecular mass basis.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{ZimmermannStopper1987,
  author    = {Zimmermann, U. and Stopper, Helga},
  title     = {Elektrofusion und Elektropermeabilisierung von Zellen : Eine neuartige Methode der Biotechnologie zur gezieltenVer{\"a}nderung der genetischen Eigenschaften von Zellen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63514},
  year      = {1987},
  abstract  = {No abstract available},
  subject      = {Toxikologie},
  language  = {en}
}
@incollection{ZimmermannStopper1987,
  author    = {Zimmermann, U. and Stopper, Helga},
  title     = {Electrofusion and electropermeabilization of cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-73065},
  publisher      = {Universit{\"a}t W{\"u}rzburg},
  year      = {1987},
  abstract  = {No abstract available.},
  subject      = {Elektrofusion},
  language  = {en}
}
@article{StopperZimmermannNeil1988,
  author    = {Stopper, Helga and Zimmermann, U. and Neil, G. A.},
  title     = {Increased efficiency of transfection of murine hybridoma cells with DNA by electropermeabilization},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63488},
  year      = {1988},
  abstract  = {Dispase-treated murine hybridoma cells (SP2/0-Ag14) were transfected with the G418 resistance gene bearing plasmid pSV2-neo by electropermeabilization with a high degree of efficiency. The cells were subjected to intermittent multiple high-voltage short duration (5 p.s) DC pulses at intervals of 1 min in a weakly conducting medium followed by selection in G418-containing medium. The transfection medium, temperature, pulse duration, and voltage were empirically determined by preliminary electropermeabilization experiments. Increasing the number of pulses resulted in a higher percentage of transfected cells, but a decrease in the number of viable cells, with the optimal transfectant yield resulting when five pulses of 10 kV jcm were administered. This method allows the rapid and efficient injection of DNA into mammalian cells, and permits the rapid production of stable, drug resistant hybridoma celllines for use in subsequent fusion experiments.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{EpeHarttigStopperetal.1990,
  author    = {Epe, B. and Harttig, U. and Stopper, Helga and Metzler, M.},
  title     = {Covalent binding of reactive estrogen metabolites to microtubular protein as a possible mechanism of aneuploidy induction and neoplastic cell transformation},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63478},
  year      = {1990},
  abstract  = {Neoplastic cell transfonnation induced by estrogens and some other carcinogen\& such as benzene appears to involve the induction of mitotic aneuploidy rather than DNA damage and point mutations. As metabolic activation may also play an important roJe in the mechanism of carcinogenesis of these nongenotoxic compounds, we have studied the Interaction of reactive quinone metabolites of various estrogens and of benzene with the major microtubular protein, tubulin, in a cell-free system. Covalent binding of the radioactively labeled metabolites to the a- and 13-subunit of tubulin was found to depend on the structure of the metabolite. When the adducted tubulins were tested in vitro for their ability to polymerize to microtubules, Inhibition of microtubule assembly was obsened in every case, although to varying extents. It is proposed that the fonnation of covalent tubulin adducts may impair the formation of mitotic spindies and thus contribute to chromosomal nondisjunction and aneuploidy induction.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{StopperMetzler1991,
  author    = {Stopper, Helga and Metzler, M.},
  title     = {Carcinogenic oestrogens induce respiration deficiency mutation in yeast},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63466},
  year      = {1991},
  abstract  = {In addition to hormonal activity, genetic darnage has been proposed as an important factor in oestrogen-mediated carcinogenesis. However, as short-term tests for oestrogens usually fail to show DNA mutations, lesions other than dassie nuclear DNA mutation have to be considered. Oestrogeninduced mitochondrial darnage was studied in the yeast Saccharomyces cerevisiae. Stilbene-type, but not steroidal, oestrogens were found to induce respiration-dcficient petite mutation. The effect was inversely correlated with cytotoxicity and required aromatic hydroxyl groups at the stilbene molecule. It only occurred under growth conditions and apparently was not due to the A TPase inhibitory qualities of stilbene oestrogens. Other studies have shown that petite mutation clones, which can be induced by a variety of substances, contain altered mitochondrial DNA. The mechanism of petite mutation induction might be important in tumorigenesis by also acting on nuclear DNA or facilitating carcinogenesis by disturbance of mitochondrial function.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{TasStopperKoscheletal.1991,
  author    = {Tas, P. and Stopper, Helga and Koschel, K. and Schiffmann, D.},
  title     = {Influence of the carcinogenic oestrogen diethylstilboestrol on the intracellular calcium level in C6 rat glioma cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63459},
  year      = {1991},
  abstract  = {The ~fthetic oes~rog~n diethylsti~boestrol (DES) causes a dose-dependent elevation of the cytoplasuuc Ca concentratton m C6 rat ghoma cells. This Ca2+ rise is caused neither by Ca2+ influx nor ~-r release from the ~a2 + stores of the endoplasmic reticulum. Therefore it seems likely that DES mob!hzes Ca2+ from a nutochondrial source. The DES-induced Ca2+ signal is remarkably similar to the one mduced by the. tumou~ promotor ~hapsigargin. As this compound causes leakage of calcium from the endoplasmt~ rettculum tt ~ms posstble that DES induces a similar leakage from mitochondrial Ca2+ stores. It remaans to be estabhshed whether the DES-mediated rise in intracellular calcium is causally related to the tumour-promoting properties of this compound},
  subject      = {Toxikologie},
  language  = {en}
}