[Theory of cooperative transition of DNA complexes with multimodal ligands]. / Teoriia kooperativnykh perekhodov kompleksov DNK s mul'timodal'nymi ligandami.

The theory of the cooperative transition of DNA.ligand complexes have been developed, in which a model was implied where the multimodal ligands simultaneously interacted with DNA. Obtained formula express the dependence of the experimentally estimated values of the changes of transition point and width of transition on the concentration of the ligands. These expressions make possible to obtain the thermodynamic parameters of the interaction of the multimodal ligands with DNA (binding constants, number of base pairs corresponding to one binding site of DNA etc.) by comparing the theoretical and the experimental data.

[Interaction of DNA with divalent metal ions]. / Izuchenie vzaimodeistviia DNK s ionami dvukhvalentnykh metallov.

The interaction between the native DNA macromolecules and Ca2+, Mn2+, Cu2+ ions in solutions of low ionic strength (10(-3) M Na+) is studied using the methods of differential UV spectroscopy and CD spectroscopy. It is shown that the transition metal ions Mn2+ exercise binding to the nitrogen bases of DNA at concentrations approximately 5 x 10(-6) M and form chelates with guanine of N7-Me(2+)-O6 type. Only at high concentrations in solution (5 x 10(-3) M) do Ca2+ ions interact with the nitrogen bases of native DNA. In the process of binding to Ca2+ and Mn2+ the DNA conformation experiences some changes under which the secondary structure of the biopolymer is within the B-form family. The DNA transition to the new conformation is revealed by its binding to Cu2+ ions.

[Selective effect of ionization of nitrogen bases on the thermostability of AT- and GC-pairs of DNA]. / Izbiratel'noe vliianie ionizatsii azotistykh osnovanii na termostabil'nost' AT- i GTs-par DNK.

The ionization specific influence of nitrogen bases on thermostability of AT- and GC-pairs of DNA has been investigated by the method of DNAs melting temperature analysis. It has been shown that the change of temperature interval of DNA helix-coil transition when changing pH environment is due to specific ionization of AT- and GC-pairs of nitrogen bases.

[The effect of long-range interactions between adsorbed ligands on the DNA helix-coil transition]. / Vliianie vzaimodeistviia dal'nego poriadka mezhdu adsorbirovannymi ligandami na perekhod spiral'-klubok DNK.

The influence of different types of long-range interaction of ligands adsorbed on DNA on the helix-coil transition was theoretically considered. The contact interaction was shown to differ significantly from the long-rang one. It was shown also that even weak dependence of a long-range potential on a degree of helicity resulted in the strong changes of a DNA melting curve. This result allowed to understand the different experimental data on DNA melting in the presence of different substances which reduced AT-and GC-base pairs thermostability difference.

[DNA helix-coil transition in alkaline medium]. / Perekhod spiral'-klubok DNK v shchelochnoi srede.

Dna helix-coil transition in th alkaline medium was considered theoretically and experimentally. On the basis of the theory and experimental comparison the DNA double-stranded form deprotonation was revealed.

[Effect of aflatoxin B1 on DNA enzymatic methylation and secondary structures of the rat liver]. / Vliianie aflatoksina B1 na fermentativnoe metilirovanie i vtorichnuiu strukturu DNK v pecheni krys.

Methylation and secondary structure of DNA in rat liver versus time of aflatoxin B1 (AfB1) treatment were studied. A 50% drop in 5-methylcytosine level in liver DNA as compared with control was observed long before tumor development. Also, certain changes in DNA secondary structure were seen. The DNA changes were more pronounced in the F1 progeny of rats inoculated with AfB1 at the terminal stage of gestation.

[Selective effect of ligands on AT- and GC-pairs of DNA bases]. / Izbiratel'noe vliianie ligandov na AT- i GTs-pary osnovanii DNK.

A method is proposed for investigating the specific influence of ligands on DNA AT- and GC-pairs based on the comparison of the width of transition temperature interval of DNA with a strongly pronounced block-structure and dependence of the control DNA melting temperature on their GC-content. Such a comparison allows to define separately the contribution of nonspecific effects causing a change of the width of transition temperature interval. The method is used for studying the specific influence of beta-alanine and nu-aminobutyric acid on AT- and GC-pairs.

[DNA conformation and thermostability of aqueous solutions of beta-alanine and gamma-aminobutyric acid]. / Konformatsiia i termostabil'nost' DNK v vodnykh rastvorakh beta-alanina i gamma-aminomaslianoi kisloty.

It has been shown that at low concentrations of rare amino acids (from 10(-3) M to 10(-1) M of the substance) stechiometric complexes amino acid -- DNA are formed, which bring about partial substitution of counterions screening phosphate groups and to a change of spatial structure of DNA water molecules. The DNA-solvent molecular interactions are changed, accompanied by an abrupt decrease of helix-coil enthalpy transition which leads to the unwinding of DNA double helix. In the region of amino acid high concentrations (greater than 1-1,5 M) a rise of thermostability and winding of DNA double helix is observed. It has been established that B----C-like conformational transition stimulated by the rise of DNA thermostability is a result of counterions dehydration and the increase of effective ionic strength of the solution which is due to the rise of amino acid-zwitterions content in it.

[DNA conformation and thermostability in urea aqueous solutions]. / Konformatsiia i termostabil'nost' DNK v vodnykh rastvorakh mocheviny.

It is suggested from the character of the change of circular dichroism spectra that in the presence of urea winding of DNA double helix takes place within the bounds of B-family of forms. It is shown that the realized conformation of DNA differs from the experimentally known forms of DNA belonging to B-family. Urea destabilizes the DNA molecules without connection with helical and melt pairs of DNA nitrous bases. Urea affects the conformational state of DNA by water destruction around DNA, which is accompanied by dehydration of DNA and basic metal ions.

[Modification of DNA-specific methylation in tissues of healthy and tumor bearing (sarcoma 45) rats under the effect of an active alkylating cancerolytic agent]. / Izmenenie spetsificheskogo metilirovaniia DNK v Tkaniakh zdorovykh i opukholenosiashchikh krys (s sarkomi 45) pod vliianiem aktivnogo kantserolitika alkiliruiushchego tipa.

The content of 5-methyl cytosine (5-MC) in the DNA preparations from organs and tissues of healthy and tumour-bearing (sarcoma 45) rats and the effect of an alkylating cancerolytic agent on DNA methylation in vivo were studied. The 5-MC content in the DNA preparations from liver, spleen and testicles of tumour-bearing rats and tumour cells was increased, the maximal increase being observed in liver and spleen DNAs (1,71 and 1,70 mol.%, respectively) and in sarcoma DNA (1,93 mol.%) on the 8th post-inoculation day. On the 8th and 15th day following daily injections of the cancerolytic agent the 5-MC content in the DNAs from liver and spleen of the control animals was decreased in a number of cases almost down to normal level (1,00 mol.%). Tumour DNA did not differ from normal tissue DNA with respect to Tmelt and GC content; however, its differential melting curve revealed an additional "shoulder" within the temperature range of 56--60 degrees, which was partly removed after addition of the cancerolytic agent. It was assumed that the changes in the methylation level and secondary structure of DNA can be due to the cancerolytic activity of the preparation.