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Biomedical subjects

G Dirheimer

Publications and source records attributed to G Dirheimer.

At least 145 records · Page 8Linked to original sources
PubMed1980

[Primary structure of yeast mitochondrial tryptophan-tRNA capable of translating the termination U-G-A codon].

The primary structure of Yeast Saccharomyces cerevisiae mitochondrial tryptophane-tRNA, isolated by reversed phase chromatography and two-dimensional gel electrophoresis has been determined. It is as follows: pA-A-G-G-A-U-A-U-A-G-U-U-U-A-A-D-G-G-D-A-A-A-A-C-A-G-U-U-G-A-psi-U-U-C-A-i6 A (ms2i6 A)-A-psi-C-A-A-U-C-A-U-U-A-G-G-A-G-T-psi-C-G-A-A-U-C-U-C-U-U-U-A-U-C-C-U-U-G-C-C-A. Owing to its anticodon U-C-A-, where U represents a modified uridine, this tRNA can translate the opal codon U-G-A, which is usually a protein synthesis termination codon in cytoplasmic systems.

Base Sequence↗
PubMed1980

Action on ricin and its polypeptide chains on cultured hepatoma cells.

The effect of ricin, the glycoproteic toxin from castor beans, as well as of its two polypeptide chains A and B, was studied on hepatoma tissue cell suspension cultures (HCT). The isolated A and B chains have no action. Ricin at a 0.3 microgram/ml concentration, for 3 x 10(5) cells/ml, has a cytostatic effect which becomes cytotoxic after 72 h. This effect exists even if the cells are preincubated for 4 with ricin and washed afterwards. The protein content of the ricin-treated cells decreases. Protein synthesis measured by the incorporation of [3H]-leucine in the cell proteins begins to be inhibited after 30 min and is completely blocked after 2 h for a ricin concentration of 0.3 microgram/ml. DNA synthesis is inhibited from 1 h on. Finally the level of the DNA slows down from 3 h on, whereas the level of RNA abruptly falls between 4 and 5 h. The inhibitory effects are likely to be a consequence of protein synthesis inhibition, but a direct effect on the nucleic acids is not excluded.

Animals↗
PubMed1980

Combined action of citrinin and ochratoxin A on hepatoma tissue culture cells.

Citrinin (CTN) and ochratoxin A (OT-A) may occur simultaneously in mould-contaminated commodities. Both are cytotoxic to hepatoma tissue culture (HTC) cells. The effect of both mycotoxins, eiter alone or in association on cellular protein, RNA and DNA synthesis was tested. In the presence of ochratoxin A protein synthesis is first inhibited 30 min after the addition of the toxin and RNA synthesis after 150 min. No inhibition of DNA synthesis occurs for at least 5 h, whereas citrinin inhibits first the RNA synthesis after 10 min, second protein synthesis after 20 min and third DNA synthesis after 120 min. When both mycotoxins are added simultaneously to HTC cells the inhibition of RNA and protein synthesis occurs immediately, that of DNA synthesis after a short lag time. This suggests a cooperative effect of both mycotoxins.

Animals↗
PubMed1980

Phenylalanine prevents acute poisoning by ochratoxina in mice.

Ochratoxin-A (OT-A) a mycotoxin isolated from Aspergillus ochraceus is toxic for animals and man causing a fatal chronic kidney disease and liver damages. OT-A is a competitive inhibitor of phenylalanine in the phenylalanyl-tRNA synthetase-catalyzed reaction thus inhibiting protein synthesis. This inhibition can be reversed by phenylalanine. When injected intraperitoneally (i.p.) to mice a dose of 0.8 mg of OT-A is lethal within 24h. However, when this lethal dose is injected together with 1 mg of phenylalanine 100% of the animals survive. When phenylalanine was injected 30 min after OT-A the doses required for the survival of 92% of the animals had to be about 25 times higher.

Animals↗
PubMed1980

[Ricin, the toxic protein of the castor-oil plant (Ricinus communis L). Structure and properties (author's transl)].

Ricin is an extremely toxic phytotoxin from the castor-oil plant seeds. This toxin is different from the two phyto-hemagglutinins or lectins which are also present in the seeds and can be purified in two chromatographic steps. Studies on the physical and chemical properties of pure ricin are given (molecular weight: 65 750 daltons, glycoproteic nature, oses composition: 15 moles of mannose and 8 moles of N-acetyl-glucosamine per mole of ricin, aminoacids composition: 545, bicatenary structure: the toxin is formed by two polypeptide A and B chains linked together by a disulfure bond). Though ricin is resistant to proteolytic enzymes under normal conditions, we have found conditions in which tryptic hydrolysis of the toxin gives several peptides which retain toxicity. Two of them were purified. The LD50 on mice of ricin and its isolated toxic peptides were determined, the symptoms of ricin's intoxication were established on animals which died from a dramatic hepatonephritic injury, but always after a lag. Ricin has a cytostatic, and then a cytotoxic effect on cells in culture which are highly damaged (important membranous protrusions). The mechanism of ricin's action was studied. It inhibits elongation in protein synthesis in vivo as well as in vitro, by acting on ribosomes whether cytoplasmic, mitochondrial or chloroplastic. To act, the ricin A-chain must be activated by ribosomes which split the ricin molecule into its polypeptide chains; these ribosomes are then frozen by the toxin and became inefficients in protein synthesis.

Animals↗
PubMed1979

[Preventive action of phenylalanine on acute intoxication of ochratoxin-A].

Ochratoxin-A, a mycotoxin causing kidney and liver damage, inhibits protein synthesis by competition with phenylalanine in the phenylalanyl-tRNA synthetase catalysed reaction. A dose of 0,8 mg ochratoxine per Mouse is 100% lethal within 24 hrs, when injected intraperitoneally. When phenylalanine is injected simultaneously with ochratoxine-A, the survival of the animals was 100% for 1 mg of phenylalanine per Mouse. Ten times higher doses of phenylalanine are necessary to obtain a 85% survival if the amino acid is injected 30 min. after the mycotoxin. Phenylalanine gives a very low protection if injected 1 hr or more ochratoxine-A.

Animals↗
PubMed1979

In vitro methylation of yeast tRNAAsp by rat brain cortical tRNA-(adenine-1) methyltransferase.

Rat brain cortices from young animals contain large amounts of tRNA (adenine-1)methyltransferase(s). The enzyme(s) can methylate E. coli tRNA and to a lower degree yeast tRNA. Among yeast tRNA species which can be methylated we have selected tRNAAsp as a substrate for the brain enzyme. The digestions of in vitro methylated [Me-3H]-tRNAAsp with pancreatic and/or T1 ribonucleases followed by chromatographies on DEAE-cellulose, 7 M urea, suggested that the methylation of tRNAAsp occurred at a single position within the D-loop. Further digestion of the radioactive oligonucleotide recovered after DEAE-cellulose chromatography by phosphomonoesterase and snake venom phosphodiesterase enzymes followed by bidimensional thin layer chromatography enabled us to determine the location of the adenine residue which becomes methylated by the brain enzyme. This one resulted to be the adenine 14 in the D-loop of yeast tRNAAsp.

Animals↗
PubMed1978

Primary structure of bovine liver tRNATrp.

Purified tRNATrp from bovine liver, accepting 1700 pmol tryptophan per A260nm unit, was completely digested with pancreatic ribonuclease and T1 ribonuclease. The sequences of the resulting oligonucleotides were determined and the primary structure of the tRNA was deduced. These analyses showed numerous incomplete post-transcriptional modifications, and several positions heterogenously occupied by two different nucleotides, which lead us to think that in bovine liver there exist a mixture of several tRNATrp.

Animals↗