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Biomedical subjects

G Dirheimer

Publications and source records attributed to G Dirheimer.

At least 109 records · Page 6Linked to original sources
PubMed1985

Natural occurrence of methionine sulfoximine in the Connaraceae family.

The toxic principle of Cnestis glabra, identified as methionine sulfoximine has been found as a permanent constituent of the soluble amino acid pool of this plant. In the roots the toxin concentration varies markedly according to the developmental stage of the plant. The poisonous principles of Cnestis polyphylla and Rourea orientalis, two other Connaraceae species, were purified to homogeneity. Similarity of their physiochemical and biological properties, their behaviour in thin-layer and gas chromatographies and their infrared spectra to those of the toxin of Cnestis glabra established their identity to methionine sulfoximine. This methionine derivative, never reported as a natural product, seems to be characteristic of toxic Connaraceae species.

Animals↗
PubMed1985

Correlation between alimentary mycotoxin contamination and specific diseases.

Several pathological cases including primitive hepatomas, Reye's syndrome, alimentary toxic aleukaemia, were encountered in two different Tunisian Sahel hospitals. Contamination of some nutriments of the patients by mycotoxins (aflatoxins, trichothecenes, ochratoxin A, citrinin) are most likely involved in the origin of these diseases.

Carcinoma, Hepatocellular↗
PubMed1985

[Properties of DNA-(cytosine-5-)-methyltransferase in the brain].

Beef brain DNA-(cytosine-5-)-methyltransferase was partially purified by chromatography on Ultrogel AcA34 and Dyematrex Blue A. The purification was of 360 times and the recovery of 75%. The pH optimum of the reaction is 7.6 NaCl inhibits double stranded DNA methylation, but stimulates single stranded DNA methylation up to 50 mM, before inhibiting. EDTA (1 mM) and MgCl2 (4 mM) stimulate DNA methylation. Polyamines inhibit the reaction.

Animals↗
PubMed1985

[DNA damage in the spleen, liver and kidneys of mice treated with ochratoxin A].

Ochratoxin A a natural contaminant of feed and food has been shown to induce experimental liver and kidney tumors. Since there is a good correlation between the carcinogenic potency of chemicals and the DNA damages induced in mammalian cells treated either in vivo or in vitro by these compounds, we have measured single-strand breaks induced by ochratoxin A in DNA of liver, spleen and kidney. Our data clearly showed that ochratoxin A induced DNA damages in vitro as well as in vivo. Damages were dose-dependent, reversible and vary upon the time according to the tissue. In spite there is no report up to now on experimental leukemia induced by ochratoxin A, our results indicate that this possibility have to be considered.

Animals↗
PubMed1984

In vitro enzymatic methylation of DNA substituted by N-2-aminofluorene.

Both the initial velocity and the overall methylation of DNA substituted by aminofluorene, by a rat liver DNA(cytosine-5-)-methyltransferase, are increased as compared to native DNA. The Km and Vmax of the modified DNA for the enzyme increase as a function of the extent of modification. The carcinogen may induce a secondary structure favouring the 'walking' of the enzyme along the DNA. The hypermethylation caused by this carcinogen could have a significance in gene activity, cellular differentiation and cancer induction.

Animals↗
PubMed1984

Sequence of tRNA Ile IAU from brewer's yeast.

The nucleotide sequence of tRNAIle from brewer's yeast Saccharomyces cerevisiae was determined. Its primary structure is pG-G-U-C-U-C-U-U-m1G-m2G- C-C-C-A-G-D-D-G-G-D-D-A-A-G-G-C-A-C-C-G-U-G-C-U-I-A-U-t6 A-A-C-G-C-G-G-G-GA-D-m5 C-A-G-C-G-G-T-psi-C-G-m1 A-U-C-C-C-G-C-U-A-G-A-G-A-C-C-A-C-C-A. Its anticodon is I-A-U. It should therefore recognize the three isoleucine codons and is for this reason probably the only isoacceptor tRNA for isoleucine in brewer's yeast. It presents a large homology with its counterpart from Torulopsis utilis (87%).

Animals↗
PubMed1984

A quenched-flow apparatus which allows the measurement of the kinetics of a reaction in one stroke.

A chemical quenched-flow apparatus is described which measures, in a unique stroke, enough data points (8-11) for establishing the kinetics curve of a reaction. Only very small volumes of reaction solutions (2 X 500 microliters) are required. The time intervals between which the kinetic data may be measured range from 5 to 37 ms and from 120 to 450 ms with the corresponding mixing times of 0.6 and 5 ms, respectively. This apparatus was used to investigate the pre-steady-state domain of the aminoacylation reaction of tRNAVal by valyl-tRNA synthetase from yeast.

Amino Acyl-tRNA Synthetases↗
PubMed1984

Inhibition of protein synthesis in mice by ochratoxin A and its prevention by phenylalanine.

The sensitivity of protein synthesis to ip doses of ochratoxin A ranging from 1 to 15 mg/kg body weight has been determined in the livers, kidneys and spleens of mice. The incorporation of 14C-labelled amino acids into protein was measured in the total tissue homogenate, in the 105,000-g supernatant fraction and in the fraction of thermostable soluble proteins. The inhibition of protein synthesis was greatest in spleen and kidney and least in liver. The percentage inhibition of protein synthesis by any one dose of ochratoxin A was similar in all of the protein fractions from any one organ. The degree of inhibition of protein synthesis 5 hr after administration of 1 mg ochratoxin A/kg was 26% in liver, 68% in kidney and 75% in spleen. Phenylalanine (100 mg/kg) injected together with ochratoxin A prevented the inhibition of protein synthesis by a dose of 10 mg OTA/kg in all of these organs.

Animals↗
PubMed1983

Enzymatic methylation of chemically alkylated DNA and poly(dG-dC) X poly(dG-dC) in B and Z forms.

The enzymatic methylation of chemically alkylated DNA and of poly(dG-dC) X poly(dG-dC) by beef brain DNA(cytosine-5-)-methyltransferase have been tested. The alkylation by dimethylsulfate, which yields mostly 7 methylguanine (m7G) and 3 methyladenine (m3A) do not affect the enzymatic methylation. The dimethylsulfate alkylated poly(dG-dC) X poly(dG-dC) converted into the Z-form in the presence of MgCl2, is just as well methylated as the native or the alkylated polynucleotide in the B-form. The alkylation of DNA or of poly(dG-dC) X poly(dG-dC) by methylnitrosourea yields, in addition to the above base modifications described for dimethylsulfate, methylphosphotriesters and O6-methylguanine. The enzymatic methylation of these substrates modified by methylnitrosourea is decreased. This decrease is proportional to the extent of the chemical alkylation of the substrate.

Alkylation↗
PubMed1983

Enzymatic methylation of DNA and poly(dG-dC) X poly(dG-dC) modified by 4-acetoxyaminoquinoline-1-oxide, the ultimate carcinogen of 4-nitroquinoline-1-oxide.

Both the initial velocity and the overall methylation of Ac-4HAQO modified DNA by a calf brain DNA (cytosine-5-)-methyltransferase are increased as compared to native DNA. The affinity of the modified DNA for the enzyme decreases as a function of the extent of the modification. Heat-denatured, single-stranded DNA shows exactly the opposite results: the more it is modified, the less it is methylated. The poly(dG-dC) X poly(dG-dC) modified by 4NQO is as well methylated as the non-modified one. The carcinogen may induce a tertiary structure favouring the 'walking' of the enzyme along the DNA. The hypermethylation caused by this carcinogen could have a significance in gene activity and cellular differentiation.

Aminoquinolines↗
PubMed1983

The nucleotide sequence of methionine elongator tRNA from wheat germ.

Wheat germ methionine elongator tRNA (tRNAmMet) was purified by three column chromatogaphies followed by electrophoresis on polyacrylamide gel. Its sequence is pG-G-G-G-U-G-G-U-m1G-m2G-C-G-C-A-G-D-D-G-G-C-acp3U-A-G-C-G-C-m22G-psi-A-G-G- psi-C-U-Cm-A-U-mt6A-A-psi-C-C-U-G-A-G-m7G-D-m5C-G-A-G-A-T-psi-C-G-m1A-G2-C-C-U- C-U-C-U-C-A-C-C-C-C-A-C-C-A. Two hypermodified nucleosides, methylthreoninocarbonyladenosine (mt6A) and 3(3-amino-3-carboxypropyl)uridine (acp3U), are present in this tRNA.

Base Sequence↗
PubMed1983

Study of the interaction of yeast arginyl-tRNA synthetase with yeast tRNAArg2 and tRNAArg3 by partial digestions with cobra venom ribonuclease.

Yeast tRNAArg2 and tRNAArg3 are two isoacceptors which show similar V and Km for yeast arginyl-tRNA synthetase despite important differences in their primary structures. Fragments resulting from the partial digestion of 3' or 5' end-labelled tRNAArg2 and tRNAArg3 in the presence or absence of arginyl-tRNA synthetase by cobra venom ribonuclease, an enzyme which cuts preferentially in double-stranded regions, were analysed by electrophoresis on polyacrylamide gels. In the absence of arginyl-tRNA synthetase, major cuts were observed in tRNAArg2 and tRNAArg3 at the end of the 3' part of the acceptor stem and in the 5' part of the anticodon stem, whereas the 5' part of the acceptor stem and the 3' part of the anticodon stem are only slightly cleaved. The D and the T stems are almost fully resistant to cobra venom ribonuclease attack confirming the strong tertiary structural organization of this region. In the presence of arginyl-tRNA synthetase the two or three last sites of the 3' halves of the acceptor stems and the sites in the 3' halves of the anticodon stems are almost completely protected against ribonuclease hydrolysis in both tRNAs; 31-69% protection of the sites located in the 5' halves of the anticodon stem is also observed. However, the cleavage levels are enhanced for the three head positions in the 3' halves of the acceptor stems and a new cut appears at the first position of this region in the case of tRNAArg3. The similarity of the protection patterns of tRNAArg2 and tRNAArg3 suggests that both molecules interact in nearly the same manner with arginyl-tRNA synthetase, which in turn implies great similarities in their tertiary structure when involved in the complex. If this tertiary organization is like that described for tRNAPhe, all protected sites are located in the inside of its L-shaped model.

Amino Acyl-tRNA Synthetases↗
PubMed1983

Sequence of tRNALeu CmAA from Bacillus stearothermophilus.

The primary structure of Bacillus stearothermophilus tRNALeu was determined and found to be :pGCCGAUGs4UGGCGGAAUDGGCAGm1ACGCGCACGACUCmAAms2i6AA psi CGUGUGGGCUUUGCCCGUGUGGGT psi CGACUCCCACCAUCGGCACCA. The molecule has a large extraloop and contains only 8 minor nucleotides. There is a G at position 21 like in all other sequenced bacterial tRNAsLeu.m1A is in position 22, just before the D stem like in several other procaryotic tRNAs. The anticodon is CmAA and is adjacent to a ms2i6A in the 3'-direction.

Base Sequence↗
PubMed1983

The primary structure of yeast mitochondrial tyrosine tRNA.

The mitochondrial tyrosine tRNA from Saccharomyces cerevisiae has been sequenced. It has two interesting structural features: (i) it lacks two semi-invariant purine residues in the D-loop which are involved in tertiary interactions in the yeast cytoplasmic tRNAPhe; (ii) it has a large variable loop and therefore resembles procaryotic tRNAsTyr rather than eucaryotic cytoplasmic ones.

Base Sequence↗
PubMed1983

Enzymatic methylation of chicken erythrocyte DNA modified by two carcinogens, 2-(N-acetoxyacetylamino) fluorene and methylnitrosourea.

Both DNA-AAF and MNU-alkylated DNA are methylated less than nonmodified DNA by rat brain nuclei cytosine 5-methyltransferase purified either by chromatography on DEAE cellulose or by Dyematrex. The inhibition of methylation is proportional to the modification of the DNA, and DNA having a given percentage of bases modified with MNU is less methylated than DNA modified to the same extent with AAF. Moreover, DNA-AAF irreversibly inhibits the methylation of native DNA, whereas MNU-alkylated DNA does not inhibit the methylation of native DNA. The AAF-substituted DNA has a higher affinity for the enzyme than native DNA. However, this is probably not due to the AAF-induced local destabilization of the DNA helix, since heat-denatured DNA shows a lower affinity for the enzyme than double-stranded DNA. Addition of DNA-AAF to the enzyme preincubated with native DNA inhibits methylation, but only after a lag period. This agrees with the model in which the methylase walks along the strand to methylate cytosine residues before being detached from the DNA. AAF bound to guanine residues may block the movement of the enzyme along the helix. The in vitro hypomethylation of DNA, caused by carcinogens, could explain the in vivo observations made by several authors and could have significance in gene activity, cellular differentiation, and oncogenesis.

2-Acetylaminofluorene↗