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Biomedical subjects

A Rupprecht

Publications and source records attributed to A Rupprecht.

At least 73 records · Page 4Linked to original sources
PubMed1984

Infrared linear dichroism of oriented DNA-ligand complexes prepared with the wet-spinning method.

Oriented DNA films prepared by the wet-spinning technique have been complexed with several ligands: the anthracycline antibiotic violamycin BI, the dipeptide L-carnosine, and the oligopeptide antibiotic netropsin. The formation of the DNA-ligand complexes is accompanied by dramatic changes of the conformational flexibility of DNA. The B-A transition which occurs usually between 80% and 70% relative humidity (RH) is more or less suppressed by the ligands. Violamycin BI at a total ligand per DNA base pair ratio, rt, of approximately 0.03 and L-carnosine at rt approximately 1.5 inhibit the B-A transition of approximately 18 and approximately 0.25 base pairs per ligand molecule, respectively. Netropsin at rt = 0.2 induces a very stable B-DNA even at rather low RH (23%). The total hydration of this complex is significantly higher than for a drug-free DNA film. Netropsin-DNA complexes at rt of 0.02 and 0.01 result in an inhibition of approximately 45 base pairs per drug molecule with respect to the B-A transition.

Aminoglycosides↗
PubMed1981

Structural studies of A-form sodium deoxyribonucleic acid: phosphorus-31 nuclear magnetic resonance of oriented fibers.

A highly oriented sample of A-form sodium deoxyribonucleic acid (DNA) has been investigated by using proton-enhanced 31P nuclear magnetic resonance (NMR). Proton-decoupled spectra taken with different angles between the magnetic field direction and the fiber direction are compared to theoretical spectra which are calculated by assuming the following: (1) the orientation of the phosphate groups in the fiber is given by the A-form DNA coordinates suggested by Arnott & Hukins [Arnott, S., & Hukins, D. W. L. (1972) Biochem. Biophys. Res. Commun. 47, 1504-1509]; (2) the DNA phosphate groups may be considered stationary on the NMR time scale; (3) the relevant features of the spectra are determined solely by chemical shift anisotropy of the phosphorus atoms. The experimental and calculated spectra are in excellent agreement and support the validity of the above assumptions contrary to conclusions drawn in another investigation [Shindo, H., Wooton, J. B., Pheiffer, B. H., & Zimmerman, S. B. (1980) Biochemistry 19, 518-526]. In particular, we find no evidence to support the notion of a highly irregular phosphodiester backbone. Comparison of observed and simulated spectra allows the determination of the orientation of the 31P chemical shielding tensor relative to the bonding framework of the phosphodiester group. The orientation agrees with that expected from NMR studies of phosphodiester model compounds [Kohler, S. J., & Klein, M. P. (1976) Biochemistry 15, 967-973; Herzfeld, J., Griffin, R. G., & Haberkorn, R. A. (1978) Biochemistry 17, 2711-2718] and X-ray diffraction of oriented fibers [Arnott, S., & Hukins, D. W. L. (1972) Biochem. Biophys. Res. Commun. 47, 1504-1509].

Animals↗
PubMed1977

Free-radical formation in gamma-irradiated oriented DNA containing electron-affinic radiosensitizers.

Electron paramagnetic resonance (e.p.r.) was used to study the free radicals induced by gamma-irradiation at 77 K in oriented DNA with incorporated electronaffinic radiosensitizing compounds (4-nitroacetophenone, metronidazole, and Ro-07-0582). The observed e.p.r. spectra were compared with those obtained from pure oriented DNA, which had previously been analysed in detail and found to consist mainly of two components, arising from anion redicals on thymine, and cation radicals on guanine. The major spectral changes caused by the radiosensitizers could be explained as a considerable increase in the formation of cationic free radicals on guanine. There were also indications of the formation of anion radicals on the radiosensitizer molecules. No hydrogen-addition free radicals on thymine were observed when the radiosensitized samples were annealed, in contrast to the pure DNA samples.

Acetophenones↗
PubMed1976

X-ray-induced luminescence and optical absorption in DNA films.

For DNA films, X-irradiated at 77 K, a comparative study was performed on (a) light emission (fluorescence and phosphorescence) during irradiation, (b) afterglow and thermoluminescence, (c) optical absorption after irradiation, and (d) free-radical reactions in similar gamma-irradiatied DNA samples. Spectra are reported for the various kinds of light emission and for the optical absorption. From temperature-dependence studies, it was concluded that the light-emission phenomena are unrelated to the reactions of the free radicals as studied by electron paramagnetic resonance. The optical absorption on the other hand, is strongly correlated to the presence of free radicals in the DNA. Some mechanisms possibly involved in the observed luminescence reactions are discussed.

DNA↗
PubMed1975

Metabolism of isolated kidney tubules. Independent actions of catecholamines on renal cyclic adenosine 3':5'-monophosphate levels and gluconeogenesis.

Isolated kidney cortex tubules from starved rats have been used to study the actions of catecholamines on renal adenosine 3':5' monophosphate (Ado-3':5'-P) levels and gluconeogenesis. In accordance with previous workers, norepinephrine was found to increase glucose formation from lactate and pyruvate and to a smaller degree from malate, succinate, fumarate and glutamine. The stimulatory effect of 0.5 muM norepinephrine was additive to that of 0.1 mM Ado-3':5-P, indicating an Ado-3':5'-P-independent mechanism of catecholamine action. The effects of parathyroid hormone and oleate on gluconeogenesis were also additive to that of norepinephrine. A comparative study of the actions of different catecholamine derivatives revealed that gluconeogenesis was stimulated in parallel to the alpha-adrenergic potency of the hormones, whereas Ado-3':5'-P levels were increased according to the known beta-stimulatory potency of the agents. Although isoproterenol was by far the most effective in raising Ado-3':5'-P levels, it was without effect on glucose formation from pyruvate, when added at 0.1 muM. At the same concentration, phenylephrine, which had no effect on Ado-3':5'-P levels, was the best stimulator of gluconeogenesis. The alpha-receptor blocking agent phentolamine inhibited the stimulatory effect of catecholamines on gluconeogenesis with a 50 times higher potency than propranolol, a beta-blocking agent. The fact that the stimulatory effect of Ado-3':5'-P was also blocked by propranolol, indicated an unspecific mechanism of action of this substance. The results indicate that the stimulatory effect of catecholamines on renal gluconeogenesis are mediated by an alpha-receptor and that they are independent from the stimulation of renal adenyl cyclase by these agents.

Animals↗
PubMed1975

Antagonism between parathyroid hormone and norepinephrine on cyclic adenosine-3':5'-monophosphate (cAMP) levels in isolated tubules from rat kidney cortex.

Isolated rat kidney cortex tubules were used as a model system to study the hormonal regulation of cyclic adenosine-3':5'-monophosphate (cAMP) levels in vitro. When incubated over 15 min, parathyroid hormone increased cAMP levels 4-fold in the absence of inhibitors of cAMP phosphodiesterase. Norepinephrine in a concentration of 5-10-7 M which had itself no effect on cAMP levels under this condition, inhibited the effect of parathyroid hormone by 50%. This effect of the catecholamines could be completely abolished by the addition of an alpha-receptor blocking agent, phentolamine. The addition of an inhibitor of cAMP phosphodiesterase, in a concentration sufficient to prevent the breakdown of extratubular cAMP, potentiated hormone effects on cAMP levels. The antagonism between catecholamines and parathyroid hormone on cAMP levels was however not abolished by this treatment. This indicated that catecholamines probably inhibited parathyroid hormone stimulated cAMP formation. Since most of the cAMP was found to be intratubular, it can be assumed that norepinephrine and parathyroid hormone interact in the same cell. Proximal tubular sodium reabsorption and renal gluconeogenesis are discussed as possible events of this hormone interaction.

Animals↗
PubMed1975

Ionic base radicals in gamma-irradiated oriented non-deuterated and fully deuterated DNA.

The free radicals induced by gamma-irradiation at 77 K in non-deuterated and fully deuterated oriented samples of moist algal DNA have been studied by electron paramagnetic resonance (e.p.r.). The e.p.r. spectra from the non-deuterated sample were found to be similar to those from calf-thymus DNA studied previously. Numerical spectra simulations were performed based on the previously proposed interpretation of the DNA spectra at 77 K in terms of a mixture of two spectral components arising from anionic and cationic base radicals (probably on thymine and guanine, respectively). The simulations were found to account satisfactorily for the main characteristics of the e.p.r. spectra from both the non-deuterated and the fully deuterated algal DNA sample.

Cobalt Radioisotopes↗