Poghos O. Vardevanyan

Influence of Low Intensity Coherent Electromagnetic Millimeter Radiation (Emr) on Aqua Solution of Dna

The thermostability and density of water-salt solutions of DNA, irradiated by non thermal coherent millimeter electromagnetic waves with frequency 64.5 GHz have been investigated using the methods of spectrophotometry and densitometry. It is shown that the thermostability of DNA and density of its solutions are increased, depending on time of irradiation. It is expected that under the influence of millimeter electromagnetic radiation the hydration of DNA and ions of Na+ that are present in solution decrease. As a result, the physicochemical characteristics of DNA are changed.

Complex-formation of Ethidium Bromide with poly[d(A-T)].poly[d(A-T)].

Abstract The interaction of Ethidium Bromide (EtBr) with double-stranded (ds-) and single-stranded (ss-) poly[d(A-T)] was studied in different ionic strengths solutions. Optical spectroscopy and Scatchard analysis results indicate that the ligand interacts to both helix and coiled structures of the polynucleotide by “strong” and “weak” binding modes. The association parameters (binding constant—K—and the number of nucleotides corresponding to a binding site—n) of the strong type of interaction were found to be independent of Na+ concentration. Weak interaction occurs at low ionic strength and/or high EtBr concentration. Estimated binding parameters of EtBr with ss- and ds-polynucleotide are in good agreement with those for EtBr-B-DNA complexes. Data obtained provided an evidence for a stacking interaction of EtBr with single stranded poly[d(A-T)].

Study of ethidium bromide interaction peculiarities with DNA

The helix-coil transition of DNA-ethidium bromide complexes in an interval of ionic strength of 2.0 x 10(-3) M ≤ muNa+ ≤ 2.0 x 10(-2) M has been investigated. It has been revealed that at the certain high ligand-DNA ratios (r(b)) the transition interval of the complex-(ΔT) becomes equal to that of DNA itself (ΔTo). It has been shown that the values of r(b) at which δ ΔT=ΔT-ΔT0=0 depends on ionic strength of a solution. Further increasing of ligand concentration leads to its conversion from stabilizer into the destabilizer of the double-stranded DNA.

The influence of GC/AT composition on intercalating and semi-intercalating binding of ethidium bromide to DNA

The binding parameters of ethidium bromide (EtBr) with DNA of various GC/AT ratios were determined using absorption and fluorescence spectroscopy. Our experimental data clearly demonstrate the co-existence of fluorescing and non-fluorescing types of “strong” binding at low concentration of EtBr. The fluorescent complex corresponds to the ordinary intercalative model. The non-fluorescent complex is referred to semi-intercalative binding of EtBr. The binding constant (K) and the number of base pairs corresponding to a binding site (n) of the fluorescent (K f and n f ) and non-fluorescent (K nf, nnf) types of interactions were determined. The average size of binding site (n) is equal to 1.5 bp (absorption spectroscopy), and nf ca. 2 bp (fluorescence spectroscopy). It was shown that nnf is dependent on GC-content and total n is independent of it.

Analysis of experimental binding curves of EtBr with single- and double-stranded DNA at small fillings

In this paper, a method that allows to analyze the binding curves of ligand (EtBr) with single-stranded (ss) and double-stranded (ds) DNA, when there are at least two modes of ligand binding to DNA at small fillings has been proposed. The obtained experimental binding curves for EtBr–ssDNA and EtBr–dsDNA have two clearly expressed linear regions. These curves were analyzed by two modes: Experimental points on linear regions were described by two different lines and all experimental points were described by single curve. It was revealed that the description by single curve permits obtaining more precise data of binding parameters (i.e. binding constant and number of base pairs that bind one ligand molecule). Moreover, the proposed method permits determining the value of proportion of binding sites of each binding mode.

Kinetics of ligand binding to nucleic acids

Abstract Ligand binding to nucleic acids (NA) is considered as a stationaiy Markov process. It is shown that the probabilistic description of ligand-NA binding allows one to describe not only the kinetics of the change of number of bound ligands at arbitrary fillings but also to calculate stationaiy values of the number of bound ligands and its dispersion. The general analysis of absoiption isotherms and kinetics of ligand binding to NA make it possible to determine of rate constants of ligand-NA complex formation and dissociation.

The Phospholipid Composition of Nuclear Subfractions from Germinating Wheat Embryos

The content of phospholipids in chromatin, nuclear matrix, and nuclear membrane from wheat (Triticum aestivum L.) embryos was studied. Subfractions of intact nuclei from dry embryos were shown to differ in the content and composition of particular phospholipids. Embryo germination resulted in the redistribution of phospholipid between nuclear subfractions. A functional role of structural changes in the nuclear membrane due to this phospholipid redistribution is discussed. It is supposed that these rearrangements change nuclear membrane permeability and its surface charge.

Effect of low-energy microwaves on DNA stability in solution

DNA isolated from liver of healthy and tumor-bearing (sarcoma 45) rats was irradiated in water-salt solution with weak microwaves (64.5 GHz, 50 μW/cm2). The heat stability of DNA increased with irradiation time (a raise of 1.5°C in Tm for “tumor” DNA after 90 min, without changes in ΔT), which may be associated with dehydration of the surrounding Na+ ions.

Theoretical treatment of helix–coil transition of complexes DNA with two different ligands having different binding parameters

The melting transition of DNA–ligand complexes, allowing for two binding mechanisms to different DNA conformations is treated theoretically. The obtained results express the behavior of the experimentally measurable quantities, degree of denaturation, and concentrations of bound ligands on the temperature. The range of binding parameters is obtained, where denaturation curves become multiphasic. The possible application to the nanocomposites crystallization is discussed.

Joint interaction of ethidium bromide and methylene blue with DNA. The effect of ionic strength on binding thermodynamic parameters

Large amount of data of experimental and theoretical studies have shown that ethidium bromide (EtBr) and methylene blue (MB) may bind to nucleic acids via three modes: intercalation between two adjacent base pairs, insertion into the plane between neighboring bases in the same strand (semi-intercalation), and outside binding with negatively charged backbone phosphate groups. The aim of the given research is to examine the behavior of these two ligands at both separate and joint DNA binding. The obtained experimental data show that the effect of simultaneous binding of EtBr and MB on double-stranded DNA has a non-additive effect of separate binding. The analyses of the melting thermodynamic parameters of DNA complexes with two bound ligands suggest competitive mechanism of interaction.