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Biomedical subjects

E Palecek

Publications and source records attributed to E Palecek.

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

Osmium-induced alteration in DNA structure.

In the presence of pyridine and other ligands osmium tetroxide binds covalently to pyrimidine bases in DNA. Properties of osmium-modified native and denatured calf thymus DNA, and plasmid Co1E1 DNA were investigated by means of differential pulse polarography, absorption spectrophotometry, circular dichroism, agarose gel electrophoresis, and nuclease S1 digestion. A great difference in the reaction kinetics of native and denatured DNAs with osmium, pyridine was observed. On the ground of the slow stepwise reaction kinetics of native DNA in the initial stage of its modification by osmium it has been suggested that the primary reaction sites do not include bases contained in the intact double helix. Osmium binding to sporadic primary reaction sites (represented e.g. by bases in the vicinity of a single-strand break) in native calf thymus DNA resulted in local changes in DNA conformation limited to a close neighbourhood of the binding site. At higher osmium/nucleotide ratios disordering of the DNA structure over a region extending beyond the immediate binding site was observed. With denatured DNA the same type of structure disordering was detected already in the initial stage of the reaction at osmium/nucleotide ratios as low as 0.01. Osmium binding to the supercoiled Co1E1 DNA resulted in its relaxation without nicking and it increased its sensitivity to linearization by cleavage with nuclease S1. The behaviour of Co1E1 DNA has been explained by the formation of a denatured region in the molecule (accompanied by a coupled loss of duplex and superhelical turns). It has been suggested that osmium can be used to label and to visualize distorted regions in the DNA double helix.

Animals↗
PubMed1983

Determination of nanogram quantities of osmium-labeled nucleic acids by stripping (inverse) voltammetry.

Modification of nucleic acids with OSO4 in the presence of pyridine results in a formation of a covalently bound electroactive center in a polynucleotide chain detectable by polarographic (voltammetric) methods. It has been shown that DNA modified with osmium (DNA-Os) accumulates at the hanging mercury-drop electrode during a waiting time in a wide range of potentials between 0 and -1.0 V (against the saturated calomel electrode) and produce at neutral pH a well-developed reduction peak at about -1.2 V due to scanning in the cathodic direction. Using the differential-pulse stripping (inverse) voltammetry, nanogram quantities of single-stranded DNA-Os can be determined at relatively short waiting times (1-3 min). Double-stranded DNA is modified with osmium to a much lesser extent as compared to single-stranded polynucleotides. The degree of modification of double-helical DNA is influenced by the presence of single-stranded and distorted double-stranded regions in the DNA molecules and by the environmental conditions which influence the DNA conformation. Osmium can thus be used as a probe of the DNA structure, and a few micrograms of double-helical DNA sample suffice for the voltammetric analysis.

Animals↗
PubMed1980

Salt-induced conformational changes of poly(dA-dT).

Conformational changes of poly(dA-dT) . poly(dA-dT) induced by increasing ionic strength were studied using CD spectroscopy. It was found that a pronounced noncooperative inversion of the long-wavelength part of the CD spectrum of poly(dA-dT) . poly(dA-dT) occurred at high concentrations of CsF in solution. It was suggested that a great difference between the geometries of the purine and pyrimidine residues in the helix was characteristic of the structure of poly(dA-dT) . poly(dA-dT) in concentrated CsF solutions.

Cesium↗
PubMed1980

Changes in DNA properties due to treatment with the pesticides malathion and DDVP.

Properties of calf thymus DNA were investigated after treatment with the pesticides malathion (0,0-dimethyl-S-(1,2-bis ethoxycarbonyl ethyl)dithiophosphate) and DDVP (0,0-dimethyl-0-(2,2 dichlorovinyl)phosphate) in vitro by means of derivative (differential) pulse polarography (DPP), thermal denaturation curves recorded spectrophotometrically (Tm), viscometric measurements, and chromatography on the hydroxyapatite column. Changes in the properties of DNA were observed by means of DPP after only a few hours incubation with the pesticides, whereas the other methods did not detect any changes even after 48 h. The results obtained by DPP indicate that single-stranded segments and thermolabile regions are formed in DNA due to the action of the pesticides. This behaviour could perhaps be a consequence of guanine alkylation followed by depurination and chain scission at elevated temperatures. Malathion and DDVP differ in the kinetics of reaction with double-helical DNA. DDVP is more reactive and its action is also manifested after 72 h in changes in viscosity, Tm, and chromatographic behaviour on the hydroxyapatite column. The changes induced by malathion were, under identical conditions, not detectable by these methods.

Animals↗
PubMed1980

Differential pulse-polarographic analysis of tobacco mosaic virus.

The tobacco mosaic virus (TMV) strain vulgare and its mutant TMV 483 (with glutamine-9 replaced by histidine) and the denatured protein of TMV vulgare were analysed by direct current (d. c.) and differential (derivative) pulse polarography (DPP) in the basic electrolyte composed of 0.001 M Co(NH3)6Cl3, 0.1 M NH4Cl and 0.1 M NH3 at 0 degrees C. The DPP method gave a substantially better resolution of the polarographic catalytic maxima A and B, but a much lower resolution of the maxima B and C, as compared with the d. c. polarographic method. The clear differentiation of the maximum A from maximum B by DPP permitted to study the variation of maximum A in the course of alkaline degradation of TMV. But for the study of TMV protein denaturation the d. c. polarography is preferable, because the denaturation is accompanied by the appearance and rise of maximum C which can be clearly differentiated from maximum B by d. c. polarography rather than by DPP. The DPP method was more, sensitive than d. c. polarography. The denatured TMV protein can be determined by DPP at concentrations around 0.1 microgram/ml.

Histidine↗
PubMed1979

Changes in the circular dichroic spectrum of calf thymus solubilized chromatin caused by ultraviolet irradiation.

UV irradiation of the chromatin caused an increase of the positive circular dichroic band in the vicinity of 275 nm (corresponding to DNA) and a deepening of the negative band of proteins at about 225 nm. These changes in the circular dichroic spectrum are monotonous in the range of doses studied (less than 6 X 10(4) J.m-2). The increase of the positive circular dichroic band probably reflects the occurrence of local conformational changes in DNA, which include changes in base position (tilting, distance from helix axis) in the close neighborhood of photoproducts. The presence of photoproducts in chromatin reduces changes in its circular dichroic spectra with temperature.

Animals↗
PubMed1978

Changes in properties of DNA caused by gamma and ultraviolet radiation. Dependence of conformational changes on the chemical nature of the damage.

Changes in the pulse-polarographic behaviour and circular dichroism spectra of DNA were investigated after gamma and ultraviolet irradiations and after degradation by DNAse I. It was found that moderate doses of radiation cause local conformational changes in the double helix, which are dependent on the chemical nature of the damage. Only the accumulation of structural changes after high doses of the radiations or after extensive enzymic treatment may cause formation of single-stranded regions in DNA.

Animals↗
PubMed1976

Interaction of nucleic acids with electrically charged surfaces. II. Conformational changes in double-helical polynucleotides.

The influence of adsorption of double-stranded (ds) DNA, ds RNA and homopolymeric pairs at a mercury electrode on conformation of these polynucleotides was studied. Changes in the polarographic reducibility of polynucleotides, which were followed by means of normal pulse polarography and linear sweep peak voltammetry at the dropping mercury electrode were exploited to indicate conformational changes. It was found that, as a consequence of adsorption of ds polynuclotides on the negatively charged electrode conformational changes similar to denaturation take place in a narrow potential region around -1.2 V (the region U). After sufficiently long time of the contact with the electrode (under our conditions about 10 s) these changes reach limiting values, which can approach total denaturation. Upon adsorption of ds polynucleotides on the electrode charged to more positive potentials than the region U either (1) no conformational changes occur or (2) only a small part of the polynucleotide (probably labile regions of the ds molecule) is very quickly denatured - the remainder of the molecule preserves its ds structure. Conformational changes of adsorbed ds polynucleotides are influenced by factors which change the stability of ds polynucleotides in solution. It is supposed that denaturation of ds polynucleotides in the region U might result from the strains connected with the repulsion of certain segments of the molecule anchored on the electrode from the negatively charged surface.

Animals↗
PubMed1975

Studies on electron transfer between mercury electrode and hemoprotein.

The electrochemical behaviour of ferricytochrome c, metmyoglobin and methemoglobin was studied using d.c., a.c. and differential pulse polarography, and controlled potential electrolysis. 1. The three hemoproteins yield d.c. polarographic steps, and peaks in differential pulse polarograms, the height of which is proportional to concentration. The charge transfer is influenced by strong adsorption. 2. The concentration dependence of the a.c. polarograms indicates structural changes in the adsorbed molecules. 3. The reduction products of controlled potential electrolysis of metmyoglobin and methemoglobin have absorption spectra identical with the native control samples. The affinity for oxygen and the cooperativity in hemoglobin are not affected by the reaction at the electrode. 4. The charge transfer proceeds via adsorbed, already reduced, molecules to freely diffusible proteins.

Binding Sites↗
PubMed1974

Structural transitions of polyadenylic acid due to protonation: the influence of the length of single strands on the polarographic behaviour of the double-helical form.

Transition of single-stranded poly(A) into its double-helical protonated form was followed by means of derivative pulse polarography, spectrophotometry, and other methods. It was found that properties of protonated poly(A) depended on the length of single strands from which the protonated double helix was formed. In contrary to longer poly(A) transition of short single-stranded molecules (s(20),w lower than about 3) caused practically no decrease in the pulse-polarographic current. It was concluded that the formation of the protonated double helix of poly(A) did not result in the inaccesibility of the reduction sites (located in the vicinity of the surface of the molecule) for the electrode process, as it was in DNA-like double-helical polynucleotides. The current changes observed in the course of transition of longer poly(A) were explained as due to slower transport of long double-stranded molecules to the electrode.

Nucleic Acid Conformation↗