ABSTRACT
The methods of UV (DUV) spectroscopy and thermal denaturation were used to study the effect of Cd2+ ions on the conformational equilibrium of three-stranded (A21, A2U) and single-stranded (poly U, poly A and poly I) polynucleotides in aqueous solutions containing 0.1 M Na+ (pH 7). An analysis of the form and intensities of DUV-spectra of poly A, poly I and A2I revealed the presence of two types of complexes: interaction with N7 of purines, resulting in the formation of macrochelates and binding to N1 of poly A and poly I. Cd2+ ions do not bind to heteroatoms of A2U nitrogen bases, and, therefore, the conformation of its structure remains unchanged up to a concentration of Cd2+ 0.01 M. A "critical" concentration (1.5x10(-4) M) of Cd2+ ions exists above which A2I transits cooperatively into a new helical conformation, which has a lower thermostability. It is supposed that, during the formation of metallized A2I, Cd2+ ions form bridges between the adenine and hypoxanthine of its homopolynucleotide circuits, being arranged inside the triple helix.
Subject(s)
Cadmium/chemistry , Nucleic Acid Conformation , Poly A/chemistry , Poly I/chemistry , Poly U/chemistry , Water/chemistry , Cations, Divalent/chemistryABSTRACT
Interaction of Mg2+, Ca2+, Cu2+ ions with the four-stranded poly(I) was studied using differential UV and visible spectroscopies. It was shown that, up to concentrations of approximately 0.1 M, Mg2+ and Ca2+ ions do not bind to heteroatoms of hypoxanthine of the four-stranded poly(I). Cu2+ ions interact with N7 (and/or N1) and O6 (through the water molecule of the hydrate shell of the ion). The latter seems to induce the enolization of hypoxanthine the deprotonation of N1, and, as a result, the transition of the four-stranded helix to single-stranded coils. Single-stranded chains form compact particles with an effective radius of about 100 A.
Subject(s)
Metals/chemistry , Poly I/chemistry , Cations, Divalent , Molecular Structure , Spectrophotometry, Ultraviolet/methodsABSTRACT
Differential UV spectra of DNA and its monomers that were induced by Ag+ ions were measured, and the effect of ions on the parameters of the helix-coil transition was studied. The data obtained confirm the existence of "strong" and "weak" modes of binding of Ag+ to DNA. The earlier proposed proton transfer from N1G to N3C, which is determined by the interaction of Ag+ with N7G (a "strong" complex), follows immediately from the shape of the differential UV spectra. The positive cooperativity of the binding of Ag+ to DNA upon the formation of a "weak" complex is due to the cooperativity of the transition of DNA to a new double-helical conformation. A model of this conformation is proposed which suggests the formation of Hougsteen GC and AT pairs.
Subject(s)
DNA/chemistry , Silver/chemistry , Cations, Monovalent , Spectrophotometry, UltravioletABSTRACT
The interaction of Ag+ ions with ribonucleotides of canonical bases in aqueous solution was studied by differential UV spectroscopy. Atoms coordinating silver ions (N7, O6 of guanosine 5'-monophosphate, N3, O2 of cytidine 5'-monophosphate, N7, N1, N3 of adenosine 5'-monophosphate and N3 of uridine 5'-monophosphate) and the binding constants characterizing the formation of appropriate complexes were determined. The differences in the relative affinity of Ag+ ions for the atoms of nucleotide bases correlate with the potential on them.
Subject(s)
Ribonucleotides/chemistry , Silver/chemistry , Adenosine Monophosphate/chemistry , Cytidine Monophosphate/chemistry , Guanosine Monophosphate/chemistry , Spectrophotometry, Ultraviolet , Uridine Monophosphate/chemistryABSTRACT
Using the method of differential scanning calorimetry, the DNA helix-coil transition was studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent copper ions at relative metal ion concentrations (Mt2+/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on relative ion concentration were determined. An aggregation of Cu(2+) + DNA complexes in the range of average ion concentration was established. It is shown that the melting enthalpy of "units" increases with copper ion concentration. The data obtained were compared with values determined by UV-spectroscopy. Association constants for Cu2+ binding to DNA were defined by the ligand theory.
Subject(s)
Copper/chemistry , DNA/chemistry , Nucleic Acid Conformation , Animals , Calorimetry, Differential Scanning , Cations, Divalent , Cattle , Models, Chemical , Spectrophotometry, Ultraviolet , ThermodynamicsABSTRACT
Using the method of differential scanning calorimetry, the DNA helix-coil transition studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent metal ions (Mn2+ and Ca2+) at relative metal ion concentrations (Me/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on the ion relative concentration were stated. The fine structure of melting curves in DNA+Me complexes was observed. The resolution degree of this structure was shown to increase in the range of moderate ion concentrations. The data obtained were compared with values determined by UV-spectroscopy. Association constants were defined for Mn2+ and Ca2+ binding to DNA by the ligand theory.
Subject(s)
Calcium/chemistry , DNA/chemistry , Magnesium/chemistry , Nucleic Acid Conformation , Animals , Calorimetry , Cattle , ThermodynamicsABSTRACT
Cryoconservation effects on macromolecular parameters of DNA from reproductive cells of fishes are studied as well as cryodamages of DNA in solutions under various freezing conditions, by the viscometry method. A dependence of the low temperature action on DNA concentration in solution and on the action duration is determined. It is stated as well that the nitrogen temperature action on the biopolymer solution results in the formation of both double- and single-stranded breaks. The cryoprotector (ethylenglycol 12%) added into the solution frozen prevents from the formation of double-stranded breaks and decreases the number of single-stranded ones. The long-term (0.5 year) keeping of the biopolymer solution at -196 degrees C both under the cryoprotector (20% 1.2-propanediol) protection and without the cryoprotector induces the significant number of single-stranded breaks. Mechanisms of cryodamages of DNA macromolecules in cells and under the nitrogen temperature action are discussed.
Subject(s)
Cryopreservation , DNA Damage , DNA/chemistry , Animals , Fishes , Humans , Nucleic Acid DenaturationABSTRACT
Experimental data on DNA melting in the presence of magnesium and calcium ions are compared with the calculated results by the "ligand" theory and "condensation" theory developed by de Marky and Manning (TMM). The maximum is observed in TMM dependences of DNA melting temperature change (delta Tm) on the ion concentration (D), absent in the experimental dependences and the "ligand" theory. The main cause of the discrepancy of calculated and experimental dependences delta Tm (D) is the fact that TMM neglects Na+ ion effects on Me2+ ion binding ("condensation") to DNA. The results obtained show that in comparison with TMM the "ligand" theory describes more adequately DNA helix-coil transition in the presence of divalent metal ions in the region of both low and high ionic strengths of solution.
Subject(s)
DNA/chemistry , Nucleic Acid Conformation , Ligands , Models, BiologicalABSTRACT
DNA complexes with Ca2+ ions formed in films at various relative humidities were studied by IR-spectroscopy for molar concentration ratio of calcium ions and DNA phosphate groups [Ca2+]/[P] = 0.4-20. It is shown that the transition of DNA complexed with Ca2+ ions into B-form occurs at higher average numbers (n) of water molecules absorbed per nucleotide: n > 18 at the ratio [Ca2+]/[P] = 10, n > 24 at [Ca2+]/[P] = 20 and n > 12 in the absence of Ca2+ ions. This shows stronger binding of water molecules in the hydrate shell of DNA-Ca2+ if compared with free DNA. The results confirm a model proposed earlier. Ca2+ ions interact with phosphate oxygens of DNA and with N(7) nitrogens of guanine forming chelated complexes.
Subject(s)
Calcium/chemistry , DNA/chemistry , Animals , Cations , Cattle , Oxygen/chemistry , Spectrophotometry, Infrared/methods , Water/chemistryABSTRACT
The properties of animal DNAs exposed to prolonged irradiation in the Chernobyl zone, have been studied by the methods of viscometry, thermal denaturation, IR-spectroscopy, and electrophoresis. High content of low-molecular fractions have been observed in the preparations of DNA from liver and spleen, their quantities increasing with age and generation of animals. This effect is especially strong in DNA from liver. Low-molecular fraction of DNA is shown to be enriched with G-C pairs and to consist of the following four fractions: 1) approximately 500 base pairs (B.p.), 2) approximately 1.5 divided by 2 thousand B.p., 3) approximately 4 divided by 5 thousand B.p. and 4) a mixture of approximately 20 thousand B.p. fragments. Further, it has been observed that the DNA preparations from the tissues of experimental animals contain about ten times higher contents of Fe, Zn, Se and other elements as compared to the control preparations.
Subject(s)
DNA/radiation effects , Power Plants , Radioactive Hazard Release , Animals , DNA/chemistry , Electrophoresis , Hot Temperature , Nucleic Acid Denaturation , Spectrophotometry, Infrared , UkraineABSTRACT
DNA with Cu2+ ions in solution and films is studied by IR and Raman spectroscopy at different relative humidities (R.H. = 51 divided by 98%). DNA complexed with Cu2+ ions is shown to transit to the double-helix conformation, passing A-form, the water content per nucleotide (n) being essentially larger: 12 for Cu2+/P = 0.4 (n = 8 for DNA without ions). Cu2+ decrease the biopolymer hydration at R.H. 50-76% interactions with Cu2+ are stated to depend on the hydration degree of macromolecules. The analysis of the absorption band shifts of Raman spectra evidences the changes in the base torsion angle around the glycoside bond to the values characteristic of the syn-conformation and the interaction both with phosphates and nitrogen bases.
Subject(s)
Copper/chemistry , DNA/chemistry , Cations, Divalent , Humidity , Nucleic Acid Conformation , Spectrophotometry, Infrared , Spectrum Analysis, RamanABSTRACT
DNA complexed with Mn2+ ions in films is studied at different relative humidities and ion contents ([Mn2+]/[P] = 0.4-1) by IR spectroscopy. It is shown that substantially more sorbed water molecules are necessary for the transition of DNA complexed with Mn2+ ions into the double helical conformation (preferentially B-form) that for macromolecules in the absence of ions. DNA-Mn2+ complexes ([Mn2+]/[P] = 1) are able to absorb more water molecules than DNA. The results of the work evidence Mn2+ ion interaction with phosphates and nitrogen bases of the macromolecule: N7G, O6G.
Subject(s)
DNA/chemistry , Manganese/chemistry , Animals , Cattle , Nucleic Acid Conformation , Spectrophotometry, InfraredABSTRACT
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.
Subject(s)
Calcium/metabolism , Copper/metabolism , DNA/metabolism , Manganese/metabolism , Animals , Cations, Divalent , Cattle , Circular Dichroism , Nucleic Acid Conformation , Spectrophotometry, UltravioletABSTRACT
The interaction of effective antibacterial drug decametoxyn with natural DNA was studied by UV-spectroscopy. Decametoxyn shows a specificity to nucleotides: it decreases the cooperativity of melting and the thermal stability of DNA parts enriched by AT pairs. The characteristics of the helix-coil transition on the DNA parts enriched by GC-pairs are invariable. Interaction with AT-pairs results in their partial or complete melting at room temperature, followed by intermolecule aggregation. Interacting with phosphates decametoxyn manifests itself not as a dication but as two single-charged ions.
Subject(s)
Anti-Bacterial Agents/pharmacology , DNA/drug effects , Nucleic Acid Conformation , Animals , Anti-Bacterial Agents/metabolism , Base Composition , Cattle , DNA/metabolism , Decamethonium Compounds/metabolism , Decamethonium Compounds/pharmacology , In Vitro Techniques , Nucleic Acid Denaturation , Spectrophotometry, UltravioletABSTRACT
By the methods of heat denaturation and luminescence the interaction between an antitumor drug prospidine and DNA in aqueous solutions at two ionic strengths (0.1 and 0.001 M NaCl) and at various prospidine concentrations was studied. For the first time it has been demonstrated that the interaction occurs at 0.1 M NaCl and therapeutic prospidine concentrations. In the framework of Frank-Kamenetsky's theory of melting of a polymer with stabilizing ligands the size of the binding site and binding constants (K) with the decrease of ionic strength, the lack of alterations in the DNA UV absorption spectrum on complex formation and the data on the competitive binding of ethydium bromide suggest that at the first stage of the reaction an external complex is formed due to electrostatic interactions between quaternary nitrogen atoms of prospidine and DNA phosphate groups. Incubation of the complex at 37 0 C leads to a decrease of the DNA melting temperature and hyperchromic effect. Presumably this is due to the relatively slow formation of chemical bonds between alkylating groups of prospidine and nucleophilic groups of DNA bases, which results in the destabilization and denaturation of DNA. It is concluded that the interaction between prospidine and DNA must be taken into consideration when studying the molecular mechanism of prospidine antitumour activity.
Subject(s)
DNA/metabolism , Piperazines/metabolism , Prospidium/metabolism , Animals , Chickens , DNA/drug effects , Erythrocytes/metabolism , Ethidium/metabolism , In Vitro Techniques , Nucleic Acid Denaturation , Prospidium/pharmacology , Spectrometry, Fluorescence , Spectrophotometry, Ultraviolet , ThermodynamicsABSTRACT
Anti-tumour antibiotic carminomycin interaction with chicken erythrocyte DNA is studied in aqueous-salt solutions by the laser polarized fluorescence method. Fluorescence quenches almost equally effectively during the antibiotic absorption on native (nDNA) and denatured (dDNA) DNAs, but the polarization degree of residual fluorescence differs about two times. Carminomycin binding to dDNA is characterized by one interaction type with a large density of occupancy sites - one antibiotic molecule per base pair. Carminomycin forms two types of complexes with nDNA, differing significantly with binding constants. Strong binding, intercalation, is saturated at one carminomycin molecule per 3 base pairs independently on the solution ionic strength. The weaker, external, interaction is characterized by the binding constant being by two orders of magnitude lower than that for intercalation, and the external interaction contribution is negligible.
Subject(s)
Carubicin/metabolism , DNA/metabolism , Daunorubicin/analogs & derivatives , Animals , Chickens , Fluorescence Polarization , LasersABSTRACT
The spectral characteristics of interacting pyrimidine bases of nucleic acids--cytosine, 1-methylcytosine, uracil in autoassociates and hydrates--are investigated using the high-resolution infrared spectroscopy in argon matrices. Shifts of vibration frequencies in simple complexes are stated to be from 10 to 30 cm-1 in the 4000-400 cm-1 region observed. The isolated state-solid phase transition is followed by the absorption maximum shift, the latter being some hundreds of cm-1 in the 4000-2000 cm-1 region and some tens of cm-1 in the 1800-400 cm-1 region.
Subject(s)
Pyrimidines/analysis , Argon , Chemical Phenomena , Chemistry , Cytosine/analogs & derivatives , Cytosine/analysis , Spectrophotometry, Infrared , Uracil/analysisABSTRACT
The influence of cuprum ions on the interaction between the antimalarial drug quinacrine (QA) and DNA is studied by polarized laser luminescence spectroscopy and fluorescence microscopy at molecular and cellular levels. An alteration of quinacrine luminescence intensity in complex with DNA caused by cuprum ions is explained in terms of redistribution of QA molecules from quenching GC- to fluorescent AT-DNA binding sites due to the competition of Cu2+ with the dye. Mechanisms of component interactions in the triplex "DNA-QA-Cu2+" in model and cellular systems are shown to be in qualitative agreement. QA photodynamic activity change caused by Cu2+ action is explained on the basis of the ideas being developed.
