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Biomedical subjects

J Kiefer

Publications and source records attributed to J Kiefer.

At least 127 records · Page 7Linked to original sources
PubMed1983

Cellular radiation effects and hyperthermia cell cycle kinetics of radiation sensitive mutants of Saccharomyces cerevisiae after X-irradiation and hyperthermia.

Radiosensitive mutants rad2, rad9, and rad51 of Saccharomyces cerevisiae were X-irradiated with 120 Gy or 60 Gy, heated at 50 degrees C for 30 min or treated with a combination of both and incubated in nutrient medium at 30 degrees C. Cell number, percentage of budding cells, and cell cycle progression were determined in 45-min intervals. Cell cycle kinetics were investigated by flow cytofluorometry. Hyperthermia leads mainly to a lengthening of G1, whereas X-rays arrest cells of the rad2 and rad9 mutant in G2 and the rad51--mutant additionaly in a state with DNA contents above G2. Cell division delay is influenced by oxygen in all strains but to a lesser extent in the rad2 mutant. The effect of the combined treatment appears to be merely additive in the rad2 and rad9 mutant while the rad51 mutant is sensitized to X-irradiation by hyperthermia. No selective action of hyperthermia on hypoxic cells was found.

Cell Cycle↗
PubMed1983

Heavy ion action on yeast cells: inhibition of ribosomal-RNA synthesis, loss of colony forming ability and induction of mutants.

The action of heavy ions (Ar to U) accelerated to specific energies up to about 10 MeV/u (u=atomic mass unit) on different functions of yeast cells was studied. Ribosomal-RNA synthesis is inhibited according to a single-hit mechanism. Inactivation cross-sections were linearly related to the ratio of the squares of the effective charge Z* and the velocity of the ions. It is concluded from the analysis that the range of the most energetic delta-electrons is larger than previously assumed. There is no such dependence for survival and induction of mutants. In both cases cross-sections increase with the ion's specific-energy indicating an important contribution of long-range delta-electrons. The analysis shows that diploid yeast is not killed by a single-hit mechanism even by very heavy ions if the track width is too small. The relative importance of the penumbral region is even more pronounced with the more sensitive strains.

Argon↗
PubMed1982

[Biological effects of heavy ion exposure].

Experiments with accelerated heavy ions may contribute to the understanding of biological radiation action. After outlining the theoretical background experiments are described which were carried out at the UNILAC-machine (Gesellschaft für Schwerionenforschung, Darmstadt, Germany) where ions up to uranium can be accelerated to maximal specific energies of 10 MeV/u. Yeast cells served as biological test systems with the synthesis of ribosomal RNA (r-RNA), colony-forming ability and mutation induction as experimental endpoints. A relationship between action and energy deposition by individual particles can be demonstrated for the inhibition of r-RNA synthesis, in other cases the ion energy plays also an important role indicating that the interaction of sigma-electrons from different particles contributes significantly to the biological effect.

Dose-Response Relationship, Radiation↗
PubMed1982

The oxygen effect in haploid and diploid yeast strains of different sensitivities.

The extent of the oxygen effect for cell survival was studied in diploid and haploid wild-type yeast and in mutants belonging to the rad2, rad6 and rad50 epistatic group. In haploids, reduced oxygen enhancement ratios were found in rad52, rad6 and rad18. The latter two also showed some influence of the mating type. In diploids the oxygen effect was decreased in rad2, rad52 and rad18.

Cell Survival↗
PubMed1982

Heavy ion effects on yeast cells: induction of canavanine-resistant mutants.

The induction of forward mutations (resistance to canavanine) by heavy ion bombardment was investigated in wild type haploid yeast Saccharomyces cerevisiae. Accelerated ions of argon, titanium, nickel, krypton, xenon, lead and uranium with specific energies between 1.7 and 9.25 MeV/u were obtained from the UNILAC machine at the Gesellschaft für Schwerionenforschung, Darmstadt/Germany. LET-values ranged from 1200 to about 15 000 keV/microns. There was no unequivocal dependence of mutation induction cross section on either LET or Z*2/beta 2, but also a prominent influence of ion specific energy. This is explained by the action of long-ranging delta-electrons.

Canavanine↗
PubMed1981

On the immunological detection of X-ray induced DNA damage.

Denatured calf-thymus DNA was X-irradiated, coupled to methylated bovine serum albumin and injected into rabbits to study the possible formation of specific antibodies. The serological activity was tested by a modified Farr-test, a micro complement binding reaction and by caesium chloride isopycnic ultracentrifugation. It was found with all assays that the immunological reaction was mainly due to unspecific DNA-binding and only a very small amount to radiation products. It seems, therefore, that this approach is not suitable for the analytical investigation of DNA damage produced by ionizing radiation.

Animals↗
PubMed1980

Cellular radiation effects and hyperthermia: cytokinetic investigations with stationary phase yeast cells.

Wild type diploid yeast, Saccharomyces cerevisiae strain 211, was subjected to 250 kV X-rays or 50 degrees C heat treatment for 30 min or to a combination of both. X-ray exposure took place either in air or in nitrogen. Cell number, percentage of budding cells and cell cycle progression was followed for up to 12 h post irradiation. The distribution of cell cycle stages was determined by flow cytofluorometry. All treatments cause a retardation of cell division rate. Hyperthermia leads mainly to a lengthening of G1, whereas X-rays arrest the cells reversibly in G2. The effect of the combined treatment appears to be merely additive. No. selective action of hyperthermia on hypoxic cells was found.

Cell Cycle↗
PubMed1980

Synthesis of inducible enzymes in irradiated yeast cells: inhibition by ionizing radiation.

The induced activity of the enzyme arginase was measured in diploid wild type Saccharomyces cerevisiae after X-ray and 241Am-alpha-particle exposure. It was found that after doses which are comparable to those necessary to reduce survival, little effect on enzyme activity is seen immediately after irradiation but it is reduced on further incubation. In this case there is an oxygen enhancement ratio of about 2 as for survival. Suppression immediately after exposure requires considerably higher doses, and no oxygen effect is seen. To achieve the same effect with alpha-particles requires even higher doses, the apparent r.b.e. is about 0 . 1. X-ray damage to induced enzyme activity is subject to liquid holding recovery. The results are discussed in relation to current theories of gene inactivation by ionizing radiation.

Alpha Particles↗
PubMed1978

Synthesis of inducible enzymes in irradiated yeast: UV effects on regulation and activity per cell.

The synthesis of two inducible enzymes in UV irradiated cells was determined during an 8 h postirradiation incubatin. In contrast to the reduction of synthesis shortly after irradiation the effect after a longer period of incubation depends on the radiation sensitivity of the strain. Since exposure inhibits division leading to different cell number in controls and irradiated samples the data are also analysed on a per cell basis. ta considerable increase of the activity per cell was observed. A maximum is reached at the end of the division delay.

Arginase↗