[Conformation and thermostability of double-stranded nucleic acids in aqueous urea solutions]. / Konformatsiia i termostabil'nost' dvuspiral'nykh nukleinovykh kislot v vodnykh rastvorakh mocheviny.

The conformation and thermostability of DNA and double-helical synthetic RNA in aqueous solutions with 0-10 M urea have been investigated. A weak dependence of DNA conformation, realized in the presence of urea, on the GC-content has been found. The increase of urea concentration leads to destabilization of DNA and synthetic RNA. The character of changes in the spectra of RNA circular dichroism at the increase of urea concentration testifies that a conformational transition (different from A----A' transition) takes place. Urea stimulates the B----Z transition in poly(dG-dC).poly(dG-dC) molecules upon NaCl addition.

[Interaction of the antineoplastic agent mitoxantrone with double-stranded nucleic acids]. / Vzaimodeistvie protivoopukholevogo soedineniia mitoksantrona s dvuspiral'nymi nukleinovymi kislotami.

The binding of mitoxantrone with double-helical nucleic acids was investigated by the methods of isothermal microcalorimetry, circular dichroism and absorption at the ionic strength mu = 0.11 and 0.011 M NaCl at temperature region of 30 divided by 60 degrees C. The investigation shows, that at mu = 0.11 M NaCl mitoxantrone interacts with double-helical nucleic acids in one way only. For such conditions using spectrophotometric titration data Scatchard plots for the binding of mitoxantrone with double-helical nucleic acids were constructed. The calculations show that the saturation stoichiometry is one mitoxantrone molecule per 2 divided by 3 base pairs DNA and 6 divided by 8 base pairs RNA. The dependence of binding constant from GC-content is observed. It is shown that the binding enthalpy of mitoxantrone with DNA and RNA increases linearly and reaches -(3.0 +/- 0.5) kkal per 1 mol mitoxantrone. It is shown that a binding mitoxantrone with double-helical nucleic acids, besides the intercalation of rings, a determinate contribution in the binding is given also by electrostatic interaction of side chains mitoxantrone with nucleic acids.

[Interaction of ethidium bromide with synthetic double-stranded polyribonucleotides]. / Vzaimodeistvie bromistogo étidiia s sinteticheskimi dvuspiral'nymi poliribonukleotidami.

The interaction of ethidium bromide (EtBr) with double helical synthetic polyribonucleotides poly(G).poly(C), poly(A).poly(U) and poly(I).poly(C) has been investigated by the method of isothermal microcalorimetry and according to the character of changes on the spectra of circular dichroism, absorption and fluorescence at binding. The calculations showed that at binding of EtBr with poly(A).poly(U) the saturation stechiometry was one EtBr molecule per 2 base pairs with binding constant (2.5 +/- 0.5).10(6) M-1 at 30 degrees C and 0.1 M. NaCl. In the case of binding of EtBr with poly(G).poly(C) and poly(I).poly(C) the saturation stechiometry was not less than 0.2 EtBr molecule per 1 base pair with binding constant (4 +/- 1).10(3) M-1 and (1.5 +/- 0.3).10(4) M-1 respectively, at 25 degrees C and 0.1 M NaCl. The binding enthalpies of EtBr with poly(A).poly(U) and poly(G).poly(C) have been determined to be (-7.5 +/- 0.5) Kcal per 1 mol of bound EtBr in average for both polymers. It has been shown that the observed strong selectivity of EtBr binding with polyribonucleotides is of entropic origin.

[Spectroscopic study of the effect of binding of bivalent manganese ions on the conformation of polyriboadenylic acid]. / Spektroskopicheskoe issledovanie vliianiia sviazyvaniia ionov dvukhalentnogo margantsa na konformatsiiu poliriboadenilovoi kisloty.

UV-differential spectra and CD spectra of poly(A) were studied in the presence of manganese ions at 10(-3) and 0.1 M Na+ in solution. It was shown that at at both low and high ionic strengths Mn2+ ions in low concentrations form bindings with phosphates of the polymer, increasing the degree of its helicity. At higher concentrations Mn2+ ions start to bind with poly(A) bases leading to a conformational helix-random coil transition. With manganese contents exceeding 10(-3) M, aggregates are formed, in which the mutual orientation of bases is characterized by a high degree of order. The calculation of concentration dependences of Mn2+ - poly(A) base binding constants shows that the process is cooperative. As the ionic strength increases from 10(-3) to 0.1 M Na+, the constant of the poly(A) - Mn2+ complex formation decreases by about an order of magnitude.

[Features of the interaction of antitumor mitoxantrone compounds with sarcoma 45 tumor DNA]. / Osobennosti vzaimodeistviia protivoopukholevogo soedineniia mitoksantrona s DNK opukholi sarkomy 45.

The interaction of antitumoral drug mitoxantrone with DNA of the tumor sarcoma 45 and healthy animals liver has been investigated according to the character of changes on the absorption spectra at binding at 30 degrees C and 0.11 M NaCl. The investigation shows that the interaction of mitoxantrone with DNA of sarcoma 45 differs from that with DNA of healthy animals liver. The calculations show that the saturation stoichiometry by both DNA is one mitoxantrone molecule per 2.5 base pairs with the binding constant k = 4 x 10(5) M-1 (for binding mitoxantrone with liver DNA) and k = 3 x 10(6) M-1 (with tumor DNA). Possible reason of such a difference is discussed on the basis of structural peculiarities of tumor DNA.

[Structural characteristics of DNA from sarcoma 45]. / Strukturnye osobennosti DNA opukholi sarkomy 45.

It is shown that thermodynamical parameters of thermal melting and the content of 5-methylcytosine for tumor DNA of sarcoma 45 differ from DNA in the norm. The reason of such difference is the presence of regions with changed DNA structure in sarcoma 45, which occurs apparently owing to hypermethylation of cytosine in tumor DNA.

[Netropsin does not bind with the oligonucleotide d(GCGATCGC)]. / Netrpsin nesviazyvaetsia s oligonukleotidom d(GCGATCGC).

By the method of circular dichroism we have studied binding of netropsin in a solution with self-complementary oligonucleotide d(GCGATCGC). It is shown that the presence of two successively located A and T nucleotides is not enough for binding netropsin with B-DNA.

[Binding of mitoxantrone and ametantrone with poly(d(G-C)) on the B---Z transition, stimulated by NaCl]. / Sviazyvanie mitoksantrona i ametantrona s poli]d(G-Ts)], vliianie na perekhod V---Z, stimulirovannyi NaCl.

Binding of antitumoral preparations mitoxantrone and ametantrone with right and left helical DNA was investigated. B-Z conformational transition stimulated by NaCl in the molecules of poly[d(G.C)].poly[d(G-C)] in complex with mitoxantrone and ametantrone was studied by the method of circular dichroism. It was shown that these compounds disturb B-Z transition but do not inhibit it.

[Circular dichroism spectra of rat liver chromatin upon exposure to hydrocortisone and insulin]. / Spektry krugovogo dikhroizma khromatina pecheni krys pri vozdeistvii gidrokortizona i insulina.

It was shown by the circular dichroism method that hydrocortisone and insulin have a synergetic effect on the structure of chromatin in vivo. The effect of hydrocortisone and insulin on chromatin is mediated and determined by intracellular regulatory mechanisms.

[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.

[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.

[Effect of phosphemide in combination with dexamethasone on DNA structure in sarcoma 45]. / Vliianie fosfemida v sochetanii s deksametazonom na strukturu DNK sarkomy 45.

It is shown that under the influence of phosphemide in combination with dexamethasone some characteristics of tumour DNA (content of 5 methyl cytosine, temperature, interval and enthalpy of melting) approximate the corresponding characteristics of DNA of healthy animals' liver better than under the influence of phosphemide only.

[A novel method of analysis of ligand-polynucleotide adsorption isotherms]. / Novyi metod analiza izoterm adsorbtsii ligandov s polinukleotidami.

The adsorption of ethidium bromide on the synthetic double-stranded polyribonucleotide poly(G)poly(C) was investigated by adsorption spectroscopy. The adsorption isotherms were analyzed in the framework of the Crothers-Gursky model. It was shown that adsorption parameters (e.g., binding constant) may also be determined from the analysis of dispersion of some bound molecules. In some cases this method may be more convenient.

[Features of melting of DNA complexes with mitoxantrone at low concentrations]. / Osobennosti plavleniia kompleksov DNK s mitoksantronom pri malykh kontsentratsiiakh.

The melting of DNA complexes with the anticancer mitoxantrone preparation at the mu = 0.11 and mu = 0.011 NaCl ionic strengths was investigated by the methods of microcalorimetry and spectrophotometry. It was shown, that at the 0.011 M NaCl the dependence of the melting temperature (Tm) upon the mitoxantrone concentration passed at minimum. The decrease of Tm was observed in the region, where one mitoxantrone molecule fell approximately on 100 base pairs DNA. There was observed a deeper minimum for DNA sarcoma 45. In the region of the mitoxantrone concentration the enthalpy of melting of the complexes increases linearly with the increase of the mitoxantrone concentration. The mentioned regularities were not observed at the mu = 0.11 M NaCl. The observed phenomenon is explained qualitatively by the entropy increase of the coiled state of DNA ligand complex on account of additional freedom of ligand's revolving.

[Comparative study of three antineoplastic alkylating agents on DNA]. / Sravnitel'noe issledovanie vliianiia trekh alkiliruiushchikh protivoopukholevykh preparatov na DNK.

The influence of three alkylating anticancer preparations phosphamide, sarcolysine, cyclophosphane on content of the 5-methylcytosine and parameters of the melting DNA of the liver healthy animals and tumor sarcoma 45 was investigated. It was shown, that among the investigated preparations cyclophosphane has stronger anticancer influence and comparatively weaker side effect on DNA liver. We came to the conclusion that it is preferable to use this preparation.

[The study of the interaction of antineoplastic drugs mitoxantrone and ametantrone with DNA using the analysis of changes in circular dichroism spectra]. / Issledovanie vzaimodeistviia protivoopukholevykh soedinenii mitokcantrona i ametantrona s DNK po kharalteru izmeneniia spektora krugovogo dikhroizma.

The influence of the ionic strength and temperature of medium on the changes in the geometry of the double stranded DNA of different nucleotide content upon the formation of complexes with antitumor drugs mitoxantrone and ametantrone was investigated. It is shown that from circular dichroism spectra it is possible to determine the relative intensity of changes in the geometry of DNA double helix upon binding with the drugs investigated. The binding of one ametantrone molecule causes greater changes in the geometry of DNA double helix than the binding of mitoxantrone.

[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.