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Biomedical subjects

I A Kuznetsov

Publications and source records attributed to I A Kuznetsov.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

[Thermal denaturation of DNA in concentrated salt-free solutions: comparison of microcalorimetric and spectrophotometric data].

Scanning microcalorimetry and spectrophotometry were used to study the dependence of melting enthalpy (delta Hm) and temperature (Tm) on DNA concentration in salt free solutions and on NaCl concentration in solutions with constant DNA concentration. This data is used to calculate the Manning's charge density parameter which is found to be equal 1.8. The linear dependence of Tm on the logarithm of DNA concentration in salt free solution was obtained. An approximate evaluation of dissociation degree in native DNA at different concentrations was made by comparison of straight lines in the Tm = f(lg CNaCl) and Tm = f(lg Cp) coordinates.

Animals↗
PubMedDate not supplied

[Demonstration of three protonated forms of poly(A): potentiometric and conductometric study of isoionic solutions].

It is shown that there are three parts on the potentiometric titration curves of isoionic solutions of poly(A) ascribed to the three protonated structures. Double-helical protonated structures are especially stable in isoionic solution. These parts on potentiometric curves are attributed to the single-stranded poly(A), to the completely protonated double-stranded poly(A+).poly(A+), and to the semiprotonated poly(A+).poly(A) structures: D, A, B forms of poly(A), respectively. pK0 values of these forms are calculated. The D form portion is found to be about 18% in isoionic solution, 40% in KCl solution (from 0.01 to 1.0 M), 40% in solution, containing 1.2 X 10(-3) M MgCl2 and 70% in 8 X 10(-4) M MgCl2 solution. The increase of MgCl2 concentration up to 8 X 10(-4) M leads to complete degradation of the double-helical structure. Only single-stranded D form exists in 5 X 10(-3) M MgCl2 solution. About 5-7% of all protons become inaccessible for titration in all solutions containing KCl and in the presence of small amounts of MgCl2. This phenomenon can not be explained by aggregation of poly(A), because all protons become accessible for titration in more concentrated MgCl2 solution when aggregation of poly(A) is significant and accompanied by the precipitation of sediment insoluble in NaOH. The supposition is made, that unprotonated double-stranded poly(A) can exist in salt-free solution at neutral pH. It is this form that is protonated with decrease of pH.

Chemical Phenomena↗
PubMedDate not supplied

[The causes of hydration changes during DNA protonation].

Changes of DNA hydration provoked by protonation in the way of Na+- and H+-ions exchange, and in the way of HCl addition to Na+-DNA, were analysed by IR-spectroscopy. Water is shown not to contribute essentially to the formation and stabilization of conformations arising when DNA is protonated. The differences between hydratation of DNA protonated by different ways are in the main accounted for by alteration of the quantities of Na+ and Cl- ions forming the aqueous-salt envelope of polynucleotide.

Animals↗
PubMedDate not supplied

[Irreversible secondary structure changes in concentrated aqueous solutions of DNA].

"Aqueous" and "electrolytic" solutions of DNA from chicken erythrocytes different concentrations of NH4Cl have been investigated. Solutions of the first type were prepared from concentrated aqueous solutions of DNA and the second type solutions by solving a solid DNA in a supporting electrolyte. Studies of the melting curves showed that even the concentrated aqueous solutions of DNA were not completely native. The changes of the secondary structure of DNA caused by solving in deionized water are irreversible. This is confirmed by the abnormal dependence of melting temperatures of DNA on the ionic strength of aqueous solutions that is not characteristic for electrolytic solutions, that is not characteristic for electrolytic solutions. It has been shown that the type of dependence of the melting temperatures on the ionic strength is a more precise test of the secondary structure of DNA than a molar extinction or hyperchromic koefficient.

Ammonium Chloride↗
PubMedDate not supplied

[Rheological properties of salt-free solutions of H+- and Na+-DNA].

Rheological properties of the water solutions of H+- and Na+-DNA were studied at shear rates in the range of 0.12-126 sec-1. It was found that the concentration dependences of reduced viscosity of these systems have the maxima which displaced to the left along abscissa after ultrasonic degradation or long keeping and to the right after the salt or urea addition. Na+-DNA solutions have the rheological curve of flow typical of pseudoplastical systems (RCF-1): the viscosity decreases with increasing shear rate. H+-DNA solutions undergo RCF-1 RCF-2 transition leading to reverse dependence of viscosity on shear rate after long keeping or sonicating (i. e. the systems become dilatant). At centrifugation and in shear fields RCF-2 RCF-1 transition occurs. Urea prevents both transitions. These discovered phenomena as well as weakening of the dilatant properties in concentrated H+-DNA solutions allow us to assume that in these systems exist circular structures consisting of single strands of DNA associated by means of ionic bonds between phosphates and protonated bases. Rheological behaviour of DNA obtained by the method of Georgiev and Struchkov was explained by the presence of circular double stranded DNA molecules in their preparations. The analysis of the non-equilibrium behavior of water solutions of DNA allows to determine the rate constants of H+- and Na+-DNA unwinding.

Animals↗
PubMedDate not supplied

[Interaction of immobilized DNA with alkaline metal and ammonium ions].

Ion exchangers with various capacities (0.1-0.2 mg-equiv/g of dry gel) are synthesized by means of immobilization of DNA in polyacrylamide gel. Exchanges of alkali metal cations and ammonium are studied on these exchangers and selectively coefficients are determined. The following selectivity series of immobilized DNA in reference to the above-mentioned cations is stated: Li+ greater than or equal to NH4+ greater than or equal to Cs+ greater than Rb+ greater than K+ greater than or equal to Na+. The peculiar properties of Li+ and NH4+ in this series are noted and a possible explanation of this fact is offered. A supposition regarding the reduced activity of water in the polyacrylamide gel containing DNA is made.

Ammonia↗
PubMedDate not supplied

[Interaction of Cu2+ and Ca2+ ions with DNA immobilized in polyacrylamide gel].

Interaction of cupric and calcium ions with DNA entrapped in acrylamide gel was studied by means of ion-exchange method. Ion-exchangers on the basis of DNA were obtained by polymerization of acrylamide with and without warming-up. Samples of DNA with different degrees of denaturation were also used for preparation of ion-exchangers. It was demonstrated that ion-exchange capacity is determined by the number of phosphate groups of DNA entrapped in gel. Cu2+ and Ca2+ ion-exchange equilibrium on the macromolecules of immobilized DNA was studied at different temperatures. Ion-exchange equilibrium constant alpha Cu2+ Ca2+ was shown to vary from 1,9 to 8,2 an increase of selectivity for Cu2+ ions taking place under conditions favouring denaturation of DNA. Stoichiometric ratio between the quantity of the phosphate groups and the number of equivalents of Cu2+ and Ca2+ was observed in all the experiments. Lack of over-equivalent absorption of CuCl2 on the DNA molecules indicates that chloride ions do not participate in charge neutralization within the Cu2+.DNA complex. It means that Cu2+ ions interact with phosphate groups of DNA coordinate simultaneously with DNA bases only.

Acrylic Resins↗
PubMedDate not supplied

[Structural parameters of charge density, macroion mobility and dissociation constants of the phosphate groups from conductivity measurements of salt free solutions of poly(U) and its salt].

Equivalent conductivity (lambda MeP) was studied for the Li+, Na+, K+, Cs+, NH4+ salts of poly(U) and for polyribouridilic acid. Concentration of the salt free solutions of poly(U) ranges from 1 . 10(-4) M-3 . 10(-3) M. Limiting equivalent conductivity (lambda 0 MeP) was obtained based on linear dependence of lambda MeP on Cp1/2 (where Cp is the concentration of nucleic phosphorus). The lambda 0 MeP values obtained were shown to increase linearly with the increase of the limiting mobility of counterion. These data were used to calculate limiting mobility of macroion (lambda p = 43 Ohm-1 Cm2 equiv-1) and parameter xi = 1.13 which characterizes charge density on a macroion. Linear dependence was shown to take place for poly(U) acid and it's salts in the Ostwald's coordinates; moreover, pK value for the phosphate groups is practically independent of the counterion's nature and equal 1.93 +/- 0.32.

Cations, Monovalent↗
PubMedDate not supplied

[Ion-exchange properties of immobilized DNA: influence of the polymer concentration and the solvent nature on the exchange of alkali metals].

The method of ion exchange on immobilized DNA, which allows to determine quantitative parameters of ion binding with a high precision, is used for studying of DNA ion selectivity. Insoluble ion exchangers on the DNA basis with the exchange capacity of 0.09 and 0.17 mg-equiv. per 1 g of dry gel are synthesized by means of immobilization of DNA gel in polyacrylamide gel. Constants of ion-exchange equilibrium for the exchanges K+-Na+ and K+-Li+ are determined on these exchangers in water and 50% water-dioxane solution. It is shown that DNA binds selectively only Li+. The selectivity to Li+ increases with the increase of DNA concentration in gel. The specific properties of Li+-DNA in solutions and in the solid state, for example, the impossibility of the B-A transition, are discussed. The selectivity reversal in favor of K+ is observed in water-dioxane solution. The cause of the selectivity reversal and the question of possible participation of cell polyelectrolytes in creation of ion gradients in the living cell are discussed.

Animals↗