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Biomedical subjects

A Gebhardt

Publications and source records attributed to A Gebhardt.

24 records · Page 2Linked to original sources
PubMed1985

Phosphatidylinositol turnover and transformation of cells by Abelson murine leukaemia virus.

The transforming protein of the Abelson murine leukaemia virus encodes a protein-tyrosine kinase. Previously, we have shown that in Abelson-transformed cells, the Abelson kinase regulates the phosphoserine content of ribosomal protein S6. Phorbol 12-myristate 13-acetate (TPA), which activates protein kinase C, induces the phosphorylation of S6 at the same five phosphopeptides as found in S6 isolated from Abelson-transformed cells. We have investigated three models whereby the Abelson kinase might regulate S6 phosphorylation via the activation of protein kinase C. First, the Abelson kinase could phosphorylate protein kinase C on tyrosine. However, we do not detect significant amounts of phosphotyrosine in protein kinase C in vivo. Second, it has been suggested that protein-tyrosine kinases might phosphorylate phosphatidylinositol. This could increase the intracellular levels of diacylglycerol and thereby activate protein kinase C. Our data strongly suggest that direct phosphorylation of phosphatidylinositol by the Abelson protein-tyrosine kinase has no physiological role. Third, an indirect activation of protein kinase C may occur via an increase in the rate of phosphoinositide breakdown. We have found that phosphoinositide breakdown appears to be constitutively activated in Abelson-transformed cells. The implications of these observations are discussed with regard to S6 phosphorylation and the mechanism of Abelson-induced transformation.

Abelson murine leukemia virus↗
PubMed1984

Rous sarcoma virus p19 and gp35 can be chemically crosslinked to high molecular weight complexes. An insight into virus assembly.

We have used the method of chemical crosslinking in order to determine the spatial interactions between components of Rous sarcoma virus. A high molecular weight complex formed by crosslinking has been isolated by ultracentrifugation on sucrose density gradients containing 0.1% (w/v) sodium dodecyl sulphate. This complex is composed of the two viral glycoproteins gp85 and gp35, the gag protein p19, and the viral RNA. Two types of bonding are important for the formation and stability of the complex: first, native disulphide bonds between gp85 and gp35 and between individual p19 molecules; and second, hetero-crosslinking between gp35 and p19 as well as homo-crosslinking between p19. Although viral RNA is quantitatively present in the complex, experiments with RNase treatment show that it is not essential for its formation or stability. A small amount of lipid is present in the complex and appears to be crosslinked to p19. In vitro-labelling of purified virus with the lipophilic photoactivatable reagent [125I] iodonaphthylazide resulted in the labelling of gp35 and p19/23. In vivo-labelling of virus with [3H]palmitate resulted in only gp35 becoming labelled. These results substantiate the membrane association of these proteins. The significance of the interactions in the high molecular weight complex for the stability of the virus and, by implication, the role which they may play in viral assembly are discussed.

Avian Sarcoma Viruses↗
PubMed1984

[Comparative studies of tocainide and propafenone in the treatment of ventricular arrhythmias].

In 15 patients with ventricular arrhythmias without previous treatment the effectiveness of 2-amino-2',6'-dimethylpropionanilide (tocainide, Xylotocan) and propafenone was compared in a cross-over-trial. 14 Patients had ventricular arrhythmias of the Lown classification IVa-V, 1 patient of Lown classification III. In 3 patients after the first course of tocainide resp. propafenone no change in therapy was made because of reducing the Lown classification by two or more grades. All patients had 24-h-ECG-Holter-Monitoring before, at the 4th day before change of therapy, and at the 9th day of therapy. Following relevant results were found: Both tocainide (p less than 0,005) and propafenone (p less than 0,05) reduce the total amount of ventriculare premature beats (VPB) without statistical significant difference between both substances. Both tocainide (p less than 0,005) and propafenone (p less than 0,02) reduce the number of isolated polytope VPB without statistical significant difference between both substances. Only tocainide (p less than 0,005) reduces couplets, but there was no statistical significant difference to propafenone. Neither tocainide nor propafenone alone was able to make total suppression of the ventricular arrhythmias in the patients included in this study. Both substances were able to lower VPB buth with a more favourable but statistically not significant therapeutic effect of tocainide.

Aged↗
PubMed1983

Differential expression of endogenous virus glycoprotein in fibroblasts and sera of some adult chickens.

A rapid and convenient assay for the expression of endogenous retrovirus glycoprotein in adult chickens has been developed based on the enzyme-linked immunosorbent assay (ELISA) principle. This method has been standardized using the conventional chick helper factor test. In the course of establishing this method with a large number of specific pathogen-free (VALO) chickens, an interesting diversity became apparent; about 20% of the birds which, according to chick helper factor tests performed with feather follicle fibroblast cultures were negative for endogenous virus glycoprotein expression, exhibited relatively high titres of reactive glycoprotein in serum. However, in no case was a chick helper factor-positive animal negative in serological tests. The possibility of endogenous virus antigen expression which either cannot be detected in fibroblasts, or is incapable of functioning in the chick helper factor complementation, is discussed.

Animals↗
PubMed1976

Mechanism of 67Ga accumulation in normal rat liver lysosomes.

67Ga accumulates in various malignant tumors and parenchymatous tissues. It was found to be associated with the soluble fraction of lysosomes (11). The present work investigates the mechanism of 67Ga accumulation in normal liver cells. Lysosomes were isolated from rat liver after intravenous injection of carrier free 67Ga. The soluble lysosomal fraction was obtained by sonication followed by centrifugation at 105,000 xg for 2 hrs. Gel filtration on Sephadex G 25 superfine was carried out on the soluble lysosomal fraction in order to investigate the stability of the 67Ga-protein complex within the lysosomes under EDTA treatment. After treatment with 1 mM/l EDTA a considerable amount of the protein bound radioactivity was found to be liberated. In further experiments the 67Ga binding lysosomal proteins were fractionated by electrophoresis on 7% polyacrylamide gels (0.5 cm x 5.5 cm). After staining with Coomassie blue 18 separated protein bands were apparent. 67Ga distribution within the gels was assessed by direct counting of radioactivity in gel slices. A considerable amount of the intralysosomal protein bound radioactivity migrated with a relative mobility of 0.36 corresponding to a protein band of molecular weight 85,000--90,000. This peak corresponded to the peak of 67Ga-labelled purified transferrin in control gels. These data were confirmed by immunoelectrophoresis combined with autoradiography: within the soluble lysosomal fraction a slight transferrin line could be identified. We conclude that 67Ga which is transported in the blood by transferrin (23) and taken up by the hepatic cell through endocytosis (32) is accumulated in the lysosomes associated with transferrin and its degraded fragments.

Animals↗