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Biomedical subjects

G Högenauer

Publications and source records attributed to G Högenauer.

At least 55 records · Page 3Linked to original sources
PubMed1981

Affinity labeling of Escherichia coli ribosomes with a covalently binding derivative of the antibiotic pleuromutilin.

Reaction of an alkylating pleuromutilin derivative with E. coli ribosomes led to the binding of the compound to both proteins and RNA. If ribosomes of the E. coli strain MRE600 were used, mainly S18 and L2 became labeled. Ribosomes from E. coli D10 bound the reagent to S18 and frequently to L27 instead of L2. Possibly at slight difference in the structure of these ribosomes exposes different, although closely neighboring, L proteins to the reagent. The simultaneous labeling of L and S proteins seems to reflect the presence of two binding sites for the antibiotic and indicates that the binding sites are located at the interphase region between large and small ribosomal subunits. Analysis of the RNA showed that the affinity label is mainly attached to the 23S species. These data are in good agreement with the known effects of pleuromutilin derivatives on ribosomal functions.

Affinity Labels↗
PubMed1981

Ribosomal binding region for the antibiotic tiamulin: stoichiometry, subunit location, and affinity for various analogs.

Equilibrium dialysis experiments with a highly purified preparation of labeled tiamulin, a semisynthetic derivative of the antibiotic pleuromutilin, and Escherichia coli ribosomes allowed the determination of two binding sites for the drug. The binding reaction showed a cooperative effect. Of the two subunits, the 50S particle was able to bind the antibiotic in a 1:1 stoichiometry. Hence, the 50S subunit contributed predominantly to the binding energy which held the antibiotic to the ribosomes. The 30S subunit, showing no strong affinity for the drug, may be needed for the generation of the second binding site in the 70S particle. If depleted of ammonium ions, 70S ribosomes lost their binding capacity for the antibiotic. The attachment sites for tiamulin could be restored by heating the ribosomes to 40 degrees C in the presence of either ammonium ions or the antibiotic. Other pleuromutilin derivatives displaced labeled tiamulin from its ribosomal binding sites. By quantifying this competition, the relative affinity of various pleuromutilin derivatives for E. coli ribosomes was determined. The binding correlated with the minimal inhibitory concentrations of these compounds against E. coli. When compared with the minimal inhibitory concentrations of these compounds against E. coli. When compared with the minimal inhibitory concentrations against E. coli. When compared with the minimal inhibitory concentrations against Staphylococcus aureus, the correlation was less strict, but the same trend prevailed. These results suggest that the antibacterial activities of various pleuromutilin derivatives on a given test organism are mainly determined by the strength of binding to the ribosomes within the bacterial cell.

Ammonium Chloride↗
PubMed1979

[Mechanisms of R-factor coded resistance (author's transl)].

The prevalence of resistance factors (R-factors) has become a serious threat to the chemotherapeutic armament of modern medicine. These extrachromosomal elements exert their effects by supplying the harbouring bacterial cell with the genetic information for detoxifying enzymes, for the expression of biochemical mechanisms which effectively prevent antibiotic molecules from reaching their target or for the synthesis of resistant target molecules. The genes which are responsible for these effects were recently shown to reside on "transposons", genetic entities which can recombine with various DNA moieties, like plasmids, bacterial chromosomes, or the genome of bacteriophages. The transposon nature of most resistance determinants provide the bacterial world with an enormous flexibility in the response to antibiotic selection pressure. It is an absolute requirement for the future to stop further spread of R-factors by reducing the selection pressure. Doctors will have to apply antibiotics more selectively, and in animal breeding and growth promotion only those drugs should be used which are never prescribed for humans. Moreover, pharmaceutical research should be directed towards the development of compounds acting on R-factors or on their enzyme systems.

Anti-Bacterial Agents↗
PubMed1979

Escherichia coli heat-labile enterotoxin: DNA-directed in vitro synthesis and structure.

Escherichia coli heat-labile enterotoxin was synthesized in a cell-free system directed by DNA of the plasmid P307. Synthesis of the toxin, assayed by the elongation induced in Chinese hamster ovary cells, was strongly stimulated by cyclic AMP and occurred at physiological levels of Mg2+ only when the polyamine spermidine was present. Activity was abolished by heat and antisera prepared against the enterotoxins of both E. coli P263 and Vibrio cholera. Tritium-labeled enterotoxin was purified by immunoprecipitation and examined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. When gel slices were assayed for the ability to stimulate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in erythrocyte ghosts, two peaks were found, one at Mr 26,000 and frequently, but not always, another at Mr 23,000. Detection of radiolabeled protein by fluorography and scintillation counting of gel slices revealed three prominent polypeptides, two corresponding to the peaks having adenylate cyclase-stimulating activity and a further one of Mr 11,500, identical to that of the cholera subunit B. The data suggest that the E. coli heat-labile enterotoxin synthesized in the cell-free system has a subunit structure.

Animals↗
PubMed1978

The effects of tiamulin, a semisynthetic pleuromutilin derivative, on bacterial polypeptide chain initiation.

Tiamulin, a water-soluble and highly effective semisynthetic derivative of pleuromutilin leads to the formation of physiologically inactive polypeptide chain initiation complexes which readily decompose and do not enter the phase of peptide chain elongation. Once elongation has begun it continues even in the presence of tiamulin as has been shown by measuring the formation of N-acetylphenylalanine-poly(phenylalanine). The formation of abortive initiation complexes was observed regardless of whether AcPhe-tRNA of fMet-tRNA was used as an initiator or whether artificial messengers or a natural messenger, like R17 bacteriophage RNA, was used. When this drug was acting on whole cells, it led to the disappearance of polysomes. The only structures which could be detected were of the monosome size. Therefore, polysomes seem to elongate the polypeptide chains in whole cells in the presence of this antibiotic, but since effective reinitiation is blocked, the polysome pool of the cell soon becomes depleted.

Anti-Bacterial Agents↗
PubMed1978

Coding of stable 4S RNA molecules by the resistance factor R1.

With the aid of DNA-RNA hybridization experiments it was shown that an E. coli strain harbouring the resistance factor R1 contains small, stable RNA species which are capable of annealing with the DNA of this R-factor. At a higher hybridization temperature RNA molecules form the isogenic, sensitive strain could also hybridize to the R1-DNA. These RNA-species were again detected if the RNA was extracted from P. mirabilis carrying this plasmid. The fact that sulfur-labelled RNA also hybridized to the plasmid DNA seems to indicate that some of these molecules are tRNAs.

DNA, Bacterial↗
PubMed1975

The mode of action of pleuromutilin derivatives. Location and properties of the pleuromutilin binding site on Escherichia coli ribosomes.

Using equilibrium dialysis techniques it could be demonstrated that (a) the pleuromutilin derivative 14-deoxy-14[(2-diethylaminoethyl)-mercaptoacetoxy] dihydromutilin HCl binds to one site per ribosome specifically, (b) the binding constant is 1.3 times 10(7) M(-1) and (c) chloramphenicol and puromycin compete with binding of the pleuromutilin derivative. Similarly the nucleotides CpA and CpCpA also displace the unsaturated derivative of the above-mentioned pleuromutilin compound. These findings suggest that the ribosomal binding site for pleuromutilin overlaps with that for chloramphenicol and analogs of the 3'-terminus of a tRNA, like puromycin or the nucleotides CpA and CpCpA.

Anti-Bacterial Agents↗