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Biomedical subjects

V Brabec

Publications and source records attributed to V Brabec.

At least 109 records · Page 6Linked to original sources
PubMed1986

DNA modified by platinum derivatives cannot adopt the A-form.

DNA fragments from chicken erythrocytes were modified by cis-diamminedichloroplatinum(II), its trans-isomer and chlorodiethylenetriaminoplatinum(II) chloride. The conformation of the modified DNA fragments in ethanolic solutions was studied by circular dichroism spectroscopy. Non-modified DNA adopted the A-form in 81% ethanol. The modification of DNA by the three platinum compounds inhibited the B to A transition of DNA induced by high concentrations of ethanol roughly to the same extent. The results support the view that the binding of the platinum complexes to B-DNA lowers the conformational freedom of DNA so that it cannot acquire the A-conformation.

Animals↗
PubMed1986

The effect of combined treatment with platinum complexes and ionizing radiation on DNA in vitro.

The conformation of isolated calf-thymus DNA treated with cis-diamminedichloroplatinum(II) (cis-DDP) or its trans-isomer (trans-DDP) and gamma radiation in combination was investigated by means of differential pulse polarography and circular dichroism spectroscopy. The results revealed that combined treatment with antitumour active cis-DDP enhanced the extent of double-stranded distorted regions in DNA molecules. If irradiation preceded the platination, the combined effect was purely additive, while the reverse order of application of the two agents resulted in an increased effect over and above what may be expected from using the two modalities separately. These results were explained on the basis of the hypothesis that favours as a major mechanism of this combined effect the fixation by the binding of cis-DDP of DNA lesions introduced during radiation. Combined treatment with antitumour inactive trans-DDP resulted in the enhancement of single-stranded, denatured DNA yield. However, more extensive alterations in DNA conformation were observed if DNA was platinated after irradiation. The different effects of the combined treatments with cis- and trans-DDP were thought to be connected with the different destabilizing effects resulting from distinct conformational distortions induced by the two isomers.

Circular Dichroism↗
PubMed1986

Polarographic studies on the conformation of some platinum complexes: relations to anti-tumour activity.

Conformational alterations induced in DNA by the binding of various bivalent and tetravalent platinum complexes were characterized by means of differential pulse polarography and circular dichroism spectroscopy. It was found that at low levels of binding the platination of DNA markedly influenced its polarographic behaviour. The results indicated that the binding of the active anti-tumour complexes resulted in minor conformational changes in DNA when the double-stranded structure remained conserved. On the other hand, the attack by inactive anti-tumour compounds induced more severe alterations which had the character of denaturation of longer regions of the DNA molecule. It was also demonstrated that active anti-tumour tetravalent platinum complexes could react with DNA, without their prior reduction to the bivalent state, and may induce in DNA conformational changes similar to those produced by bivalent cisplatin.

Antineoplastic Agents↗
PubMed1985

Crude spectrin extraction from reticulocyte-rich blood samples.

Crude spectrin was extracted from the isolated red cell ghosts with low ionic strength buffer at 37 degrees C for 30 min. No significant alterations in crude spectrin extractability in wide range of patients with various hematologic diseases were observed. However, blood samples characterized by elevated reticulocytosis provided crude extracts with increased amount of non-heme membrane skeletal proteins. The presence of ribose in the crude spectrin extracts obtained from reticulocyte-rich blood samples indicates also the presence of nucleic acids which causes the shift of protein peak in the extract from 280 nm towards lower wavelengths. A model experiment with a normal crude spectrin extract mixed with various amounts of RNA allowed us to obtain the correction curve which served for determination of non-heme protein (crude spectrin) extractability.

Blood Protein Electrophoresis↗
PubMed1985

Raman scattering from nucleic acids adsorbed at a silver electrode.

Adsorption of nucleic acids at a silver electrode polarized to -0.6 to -0.1 V (vs. Ag/AgCl) was investigated by means of surface enhanced Raman scattering (SERS) spectroscopy. Single-stranded polyriboadenylic acid and thermally denaturated DNA adsorbed at the silver electrode yield two intense bands at 734 and 1335 cm-1 on the SERS spectra. These bands, assigned to the vibrations of adenine residue rings, were much less intense if the SERS spectra were recorded for double-helical complex polyadenylic X polyuridylic acid and native DNA. Moreover, the courses of alkaline denaturation of DNA and its digestion by deoxyribonuclease I were observed by SERS spectroscopy. The results were interpreted as support for the view that intact double-helical segments of nucleic acids are not denatured or destabilized due to their adsorption at the positively charged and roughened surface.

Animals↗
PubMed1985

Use of some snake venoms in the diagnostics of paroxysmal nocturnal hemoglobinuria (PNH).

The crude toxin of Agkistrodon piscivorus was found to produce hemolysis of PNH erythrocytes by way of complement activation, however the degree of PNH blood cell lysis was lower than in other techniques used. The crude toxins of Naja naja and Naja oxiana cause much higher hemolysis though lower hemolysis takes place in normal blood cells. In some normal persons and different blood diseases it is responsible for high hemolysis even when the complement is absent. From Naja naja toxin a fraction can be isolated which has a "specific" complement effect only on PNH blood cells. This fraction can thus be utilized in a specific test for this disease.

Complement Activation↗
PubMed1985

Polarography of cytochrome c in ammoniacal buffers containing cobalt ions. The effect of the protein conformation.

Catalytic currents yielded by cytochrome c in ammoniacal buffers containing cobalt ions at a dropping mercury electrode (Brdicka's catalytic currents) were investigated by means of direct current, differential pulse, normal pulse (NP) and phase-selective alternating current polarography. It was found that Brdicka's catalytic current of cytochrome c, (the more negative part of Brdicka's double wave, wave B) is influenced by the presence of cytochrome c denaturants in the background solution. The wave B rose with the increasing concentrations of urea and sodium perchlorate, and increased in parallel with absorbance changes at 409 and 695 nm measured for identical cytochrome c solutions. The latter absorbance changes reflect unfolding of cytochrome c molecules in the bulk of solution by these denaturants. The results of NP polarography (a technique working with large potential excursion during the drop lifetime) indicate that in Brdicka's solution cytochrome c could extensively be unfolded due to its adsorption at the mercury electrode, polarized to potentials around that of zero charge.

Ammonia↗
PubMed1985

Voltammetry of tobacco mosaic virus and its isolated protein at the graphite electrode.

The electrochemical behaviour of tobacco mosaic virus (TMV) and its isolated protein was studied using differential pulse (DP) voltammetry at a graphite electrode and by direct current (DC) polarography in Brdicka solution. TMV and its isolated protein were found to be electrooxidized at the graphite electrode in the adsorbed state. Both species yielded two oxidation peaks on DP voltammograms. The first, more negative peak, corresponded to electrooxidation of tyrosine residues, whereas the other, more positive, peak corresponded to electrooxidation of tryptophan residues. DC polarography was used to detect degradation of TMV and denaturation of TMV-protein induced by an increased pH and by the addition of urea, respectively. These structural transformations resulted in increased DP voltammetric oxidation currents as recorded using a graphite working electrode. It has been suggested that the higher oxidation currents were due to an increase in the number of tyrosine and tryptophan residues accessible to the reaction at the graphite electrode. The results of these electrochemical investigations were in a good agreement with the estimation of the accessibility of tyrosine and tryptophan residues based on the well-explored three-dimensional structure of TMV and its isolated protein.

Electric Conductivity↗
PubMed1984

Polarographic activity of the antitumor drug cis-dichlorodiammineplatinum (II). The effect of hydrolysis and trans-isomerization of the drug.

Electrochemical activities of cis-dichlorodiammineplatinum (II) (cis-DDP) and its trans isomer were studied by classical and differential pulse polarography (d.p.p.). It was shown that both isomers yielded a polarographic step or peak at about -1.6 V (vs. Ag/AgCl), which corresponded to electroreduction of the complex and to catalytic hydrogen evolution. This signal was easily measurable with the aid of d.p.p. and was suitable for investigation of the extent of hydrolysis and trans-isomerization of cis-DDP leading to the formation of toxic products. The detection limit for determination of cis-DDP and its trans isomer by d.p.p. was 1 X 10(-6) mol/l.

Chlorides↗
PubMed1984

Platinum determination in cis-dichlorodiammineplatinum(II)--DNA complexes by differential pulse polarography.

A simple polarographic assay for platinum determination in cis-dichlorodiammineplatinum(II)-DNA complexes is described. The method makes it possible to determine the free (unbound) drug in the presence of DNA or platinum-DNA complex, i.e., without a separation of free drug and macromolecular components of the solution to be analyzed. This method is based on the polarographic activity of intact cis-dichlorodiammineplatinum(II) at -1.5 V, which can be measured by differential pulse polarography even in the presence of DNA or platinum-DNA complex. The lower level of analytical utility of this method is ca. 1 X 10(-6) M (195 ng of platinum/ml).

Binding Sites↗
PubMed1984

A study of experimental hypersplenism.

Methyl cellulose syndrome induced by repeated i. p. injections of methyl cellulose (MC) was followed in experimental rats. Following application of 2--4 MC injections early haematological changes are observed including increased values of reticulocytes, development of serum aggregation factor having anti-erythrocyte antibody nature and altered filtrability of non-washed erythrocytes. Later alterations developing with further MC injections (8-32) are characterized by expressive splenic enlargement, by decrease in erythrocyte and platelet values and by additional increase in number of reticulocytes. The cause of anaemia is pooling and sequestration of erythrocytes in the spleen and haemodilution from hypervolaemia blood plasma. The decreased platelet amount is the result of reduced survival time of platelets due to their increased sequestration in the spleen. Haematological changes are normalized after splenectomy. This picture resembles to a great extent human hypersplenism.

Animals↗