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Biomedical subjects

S Michel

Publications and source records attributed to S Michel.

At least 145 records · Page 8Linked to original sources
PubMed1983

Interactions between 9-hydroxyellipticine and X rays on mammalian cell survival in vitro.

Incubation with 9-hydroxyellipticine (9-OH-E) decreases the survival of X-irradiated CHO cells. The survival decreases in the case of exponentially growing and plateau-phase cells, although cells in exponential phase of growth are more sensitive to the drug alone. Radiosensitivity increases with the drug concentration and whether the cells are incubated with the drug for 1 hr prior to or immediately after irradiation. 9-OH-E inhibits the repair of potentially lethal damage, but recovery from sublethal radiation damage is suppressed only by high drug concentrations. The interaction between 9-OH-E and X-ray damage and repair has been examined. 9-OH-E itself induces DNA single-strand breaks or alkali-labile sites which are repaired by the cells. When drug-incubated cells are X irradiated, a repair-inhibiting action of the drug is observed.

Alkaloids↗
PubMed1982

Enhancement of hyperthermia-induced cytotoxicity upon ATP deprivation.

The combined effects of hyperthermia and uncouplers of oxidative phosphorylation (dinitrophenol (DNP) or m-chlorocarbonylcyanide phenyl-hydrazone (CCCP) or 5-thio-d-glucose (5-TG) on mammalian cell survival were studied in vitro. Uncouplers were toxic towards cells treated under aerobic conditions at 41 degrees C, whereas 5-TG potentiated the effect of hyperthermia in the case of hypoxic cells. In aerobic conditions the intracellular ATP concentration was decreased upon action of uncouplers, and similar changes occurred in hypoxic cells treated with 5-TG. The results suggest that the ATP deprivation enhances the cell killing by hyperthermia.

Adenosine Triphosphate↗
PubMed1982

[Characterization of a CaCl2-dependent transfection system of Escherichia coli and T3 phage DNA].

Transfection by DNA isolated from bacteriophage T3 was studied using Escherichia coli 921/0 as host. The following conditions were found optimal: Competent E. coli 921/0 were obtained by harvesting the bacteria at the onset of late exponential growth (5 X 10(8) cells/ml) and treating the latter with 0.05 M CaCl2. Hereafter, the microbes were suspended in 50 mM Tris-HCl buffer (pH 7.2) and the concentration adjusted to 7 X 10(9) cells/ml. T3 DNA was added and the suspension kept at 0 degrees C for 15 min. Determination of the number of infectious centers was then carried out in the usual way. The efficiency of transfection under these conditions amounted to 10(4) p. f. u./microgram DNA. Preincubation of competent bacteria with T4 DNA at 0 degrees C before the addition of T3 DNA reduced the number of infectious centers. However, if T3- and T4 DNA were added simultaneously no decrease of the transfection efficiency occurred. Calf thymus DNA was without influence on transfection.

Calcium Chloride↗
PubMed1981

Influence of dimethylsulfoxide on transcription by bacteriophage T3-induced RNA polymerase.

Dimethylsulfoxide (DMSO) up to 25% (v/v) does not cause irreversible alterations of T3 DNA at 42.5 degrees C as assayed by transcription with T3-specific RNA polymerase. The optimal temperature for the formation of polyanion-resistant ternary complexes of the enzyme, T3 DNA, and nascent RNA chains is lowered by 12.5 degrees C in the presence of 20% (v/v) DMSO. The same solvent concentration, however, decreased the temperature optimal for T3 RNA chain elongation by only 2.5 degrees C, indicating that DMSO preferably affects the initiation of T3 RNA synthesis. DMSO accelerates the loss of T3-specific RNA polymerase activity at 24.5 degrees C. Nevertheless, the speed with which the binary complexes between the phage RNA polymerase and DNA are inactivated by heat (42.5 degrees C) is not altered in presence of 20% (v/v) DMSO. The binding of T3-induced RNA polymerase to T3 DNA in polyanion-resistant ternary complexes is influenced by DMSO which makes the enzyme accessible to the inhibitory action of polyvinyl sulfate. Elongation of T3 RNA chains is slowed down by 20% (v/v) DMSO.

DNA, Viral↗
PubMed1981

On the immunogenicity of ribosomes and ribosomal proteins isolated from Klebsiella pneumoniae and Streptococcus pneumoniae.

The two pathogenic species Streptococcus pneumoniae and Klebsiella pneumoniae were used to analyze the immunogenic role of proteins in ribosomal preparations. The protective activity of ribosomes prepared from either strain and further purified by washing with high-salt concentrations, followed or not by sucrose gradient separation of the particles, was identical to that of crude unwashed ribosomes. Similarly, no substantial alteration of the level of protection was observed after treatment with the antibiotic puromycin. Therefore, the immunizing efficacy of ribosomes does not appear to be due either to the nonribosomal proteins adsorbed at the surface of organelles or to the growing polypeptide chain. It seems rather to be attributable to the structural ribosomal proteins themselves, which were indeed shown to induce alone a significant level of protection.

Animals↗
PubMed1981

[Interactions between X-rays and antimitotic drugs: cellular effects (author's transl)].

The interactions between three drugs and X-rays were examined in rat hepatoma cells in vitro. Incubation with Daunomycine or 9-hydroxy ellipticine decreases the survival of both exponential and plateau phase cells, whereas cis-Pt (II) decreases the survival of plateau cells, especially irradiated in anoxia. The decrease in the Do was greater when the cells were incubated with the drugs prior to X-irradiation, and was greater in the case of plateau cells than in the case of exponential cells. The repair of potentially lethal damages was inhibited by these three compounds. However, the repair of sublethal damages was inhibited by cis-Pt II, but was modified neither by Daunomycine nor 9-hydroxy ellipticine.

Animals↗
PubMed1979

Effect of temperature on the transcription by bacteriophage T3-induced RNA polymerase.

Bacteriophage T3-induced RNA polymerase is rapidly inactivated at 42 degrees C. Addition of T3 DNA delays this process for 30 s and reduces the rate with which the enzyme activity is lost indicating that a labile binary complex between T3 DNA and polymerase must have been formed. The ternary complex between T3-specific RNA polymerase, T3 DNA, and nascent RNA chains obtained when the enzyme is incubated with T3 DNA, GTP, ATP, and UTP is stable to heat (42 degrees C) and only slowly inactivated by polyvinyl sulfate. The optimal temperature for the formation of polyanionresistant ternary complexes is 30 degrees C while the elongation of T3 RNA chains proceeds fastest at 38 degrees C.

Cell-Free System↗
PubMed1979

[Effect of temperature on RNA synthesis in Escherichia coli CRT 266 (dna Bts) following infection with bacteriophage T3].

Infection of the temperature-sensitive E. coli CRT 266 (dnaBts) with T3-phages at the temperature of 30 degrees C and 35 degrees C, respectively, induced T3-specific RNA synthesis with a maximum rate at 7 min (30 degrees C) and 4.5 min (35 degrees C) after infection. At temperatures above 40 degrees C no T3-induced RNA synthesis could be observed. Infection of E. coli CR 34--45 (dnaB+) with T3 phages at 30 degrees C, 35 degrees C and at temperatures above 40 degrees C, however, produced T3-specific RNA synthesis. The maximum of T3-induced RNA synthesis could be observed between 7 min and 3 min depending on the temperature during infection. The inability to form T3-specific RNA after infection of E. coli CRT 266 at nonpermissive temperatures may be a cause for the absence of the formation of T3 phages and lysis of the host cells.

Chloramphenicol↗
PubMed1978

[Effect of temperature on formation of lysozyme in E. coli CRT 266 (dnaB ts) after infection with bacteriophage T3].

Lysozyme formation induced by bacteriophage T3 was studied in the ts-mutant E. coli CRT 266 (dnaBts) and in the wild-type E. coli CR 34--45 (dnaB+) at different temperatures. It was found that lysozyme was formed in E. coli CRT 266, however, no lysozyme synthesis took place at 41.5 degrees C. These results indicate that the expression of the lysozyme gene is disturbed in the ts-mutant at 41.5 degrees C.

Coliphages↗
PubMed1977

[Effect of temperature on the transcription of T3 DNA b y T3-specific RNA polymerase in cell-free extracts of Escherichia coli CRT266].

Cell free extracts were prepared from E. coli CRT266 9 min after infection with T3 phages. RNA synthesis in these extracts is almost entirely due to T3 RNA polymerase. The inactivation of T3 RNA polymerase in these extracts proceeds rapidly at 42 degrees C. 90% of the activity is lost within 10 min at this temperature. Under conditions where the formation of a stable initiation complex with T3 DNA is possible, i.e., in the presence of GPT, APT, and UTP the T3 RNA polymerase becomes protected against heat inactivation losing only )0% of its activity during an exposure to 42 degrees C for 10 min. Studies on the time course of RNA synthesis have shown that reinitiation is still possible at 37 degrees C and 42 degrees C. At 44 degrees C, however, RNA synthesis stops abruptly after 3 min indicating that reinitiation does no longer take place. The elongation of already initiated T3 RNA chains is rather resistant to heat. At 44 degrees C the same elongation rates are observed as at 37 degrees C and 42 degrees C, respectively.

Cell-Free System↗
PubMed1975

[RNA and protein biosynthesis in toluene treated E. coli B].

The conditions for RNA- and protein synthesis in toluenized E. coli B are investigated. The kinetics of RNA- and protein synthesis indicate that a coupled synthesis of both macromolecules takes place in these preparations. Treatment with 1% Brij 58 alters the permeability of toluenized E. coli in such a way that the protein synthesis depends on the addition of supernatant proteins (chromotographed S100 from E. coli) and tRNA.

Bacterial Proteins↗