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Biomedical subjects

V A Sorokin

Publications and source records attributed to V A Sorokin.

At least 19 recordsLinked to original sources
PubMed2005

Mg2+ and Ni2+ ion effect on stability and structure of triple poly I.poly A.poly I helix.

The effects of Mg2+ and Ni2+ ions on the absorption spectra of IMP, single-stranded poly I and three-stranded A2I in solutions with 0.1 M Na+ (pH 7) have been studied. In contrast to Mg2+ ions, the Ni2+ ions affect the absorption spectra of these polynucleotides and IMP. The concentration dependences of the intensity at the extrema in the differential UV spectra suggest that in the region of high Ni2+ concentrations ionic complexes with poly I and A2I are formed, which are characterized by the association constants K'''I = 2000 M(-1) and K'''A2I = 550 M(-1), respectively. The shape of the DUV spectra prompts the conclusion that these complexes are formed due to the inner-sphere interaction of Ni2+ ions with N7 of poly I and A2I presumably due to the outer-sphere Ni2+-O6 interaction. The formation of the complexes leads to destruction of A2I triplexes. The dependences of the melting temperature (T(m)) of A2I on Mg2+ and Ni2+ concentrations have been measured. The thermal stability is observed to increase at the ionic contents up to 0.01 M Mg2+ and only to 2x10(-4) M Ni2+. At higher contents of Ni2+ ions, T(m) lowers and the cooperativity of A2I melting decreases continuously. In all the cases the melting process is the A2I-->A+I+I (3-->1) transition. According to the "ligand" theory, these effects are generated by the energy-advantageous Ni2+ binding to single-stranded poly I (K'''A2I < K'''I) and by the greater number of binding sites which appears during the 3-->1 transition and is entropy-advantageous.

Base Pairing↗
PubMed1996

Interaction of bivalent copper, nickel, manganese ions with native DNA and its monomers.

UV differential spectroscopy is applied to study the interaction of Cu2+, Ni2+, Mn2+ ions with deoxyribonucleotides of canonic bases (dGMP, dAMP, dCMP, dTMP) and native DNA. Heteroatoms of the bases, coordinating ions, and binding constants which characterize the formation of metal complexes are found. The affinity of the ions is lower for the deoxyribonucleotide bases than for the ribonucleotide ones. This indicates that 02' of ribose participates in the stabilization of the metal complex even under conditions close to the neutral one (pH 6). Unlike the Cu2+ ions, Ni2+ and Mn2+ ions do not interact with N3C both in monomers and polymers. This seems to be the main factor explaining why copper makes DNA transform into a structure with a quasi-Hoogsteen pairing of GC pairs. No transformations of this kind of helix-coil transitions are caused by manganese and nickel up to concentrations 4 X 10(-2) M.

Copper↗
PubMed1987

Studies of formation of bivalent copper complexes with native and denatured DNA.

The formation of Cu2+ complexes with native and denatured DNA is studied by the methods of differential UV spectroscopy, CD spectroscopy, and viscometry. On ion binding to the bases of native DNA the latter transforms into a new conformation. This transition is accompanied with a sharp increase in UV absorption and a decrease in the intrinsic viscosity though the high degree of helicity persists. Possible sites of Cu2+ ion binding on DNA of various conformations are found along with corresponding constants of complex formation.

Circular Dichroism↗
PubMed1986

[Descending pathways of the cerebral cortex to nuclear structures of the extrapyramidal system].

The connections of the neocortical structures in animal and human brains with the complex of nuclear formations of the extrapyramidal system have been studied. The authors present comparative characteristics and distribution of these connections in the nuclear and other formations of the extrapyramidal system. Both mediator (via the thalamus) and direct cortical projections toward the nuclei of the extrapyramidal system in primates, especially in humans, have been found to increase. It has been shown that the frontal cortex has closer connections with the complex of the extrapyramidal nuclei as compared with other brain lobes.

Adult↗
PubMed1985

Studies of bivalent copper ion binding to poly C.

Ultraviolet differential spectra of single-stranded poly C, taken in the presence of Cu2+ ions, are studied at various ionic strengths and temperatures. Coordinational and conformational components of these spectra are obtained. The Cu2+ ion coordination site on the polynucleotide bases is found to be N(3) and possibly O(2). The direction of the poly C absorption band shift due to ion binding and conformational transitions is established. At low ionic strengths of the solution Cu2+ ions cause the helical parts of poly C to melt. At high ones the formation of double-stranded parts was observed in addition to the above effect. The calculated concentration dependences of ion-poly C bases association constants show that binding is cooperative at any ionic strength.

Copper↗
PubMed1984

Binding of divalent copper and calcium ions to poly I.

The effect of Cu2+ ions on the ultraviolet differential ( UVD ) spectra of single-stranded poly I was studied and the coordination (delta epsilon b) and conformation (delta epsilon c) components of the spectra calculated. The comparison of delta epsilon b and the UVD spectrum of protonated IMP leads to the conclusion that N(7) of inosine-5'-monophosphate (IMP) is a coordinating site for Ca2+ and Cu2+ ions on the polymer bases. The binding of Ca2+ and Cu2+ ions causes differently directed displacements of the four absorption bands of poly I, which are observed in the wavenumber range (50-34) X 10(3) cm-1. The calculation of concentration dependencies for the association constants (K") of Ca2+ and Cu2+ ions binding to poly I bases shows that the binding is cooperative. The K" values for the poly I + Ca2+ complex are two orders of magnitude lower than those for the poly I + Cu2+ complex. At low ion concentrations, binding to the poly I phosphates predominates and increases the degree of the polynucleotide helicity. At higher concentrations the spectra are mainly affected by the ion binding to bases, which results in melting of the helical parts of poly I. At Ca2+ concentrations exceeding 10(-3) M light-scattering aggregates are formed. The degree of monomer order in them is close to that observed in multistranded helices of poly I.

Calcium↗
PubMed1983

Studies of calcium ion binding to poly A.

Ultraviolet differential spectra of poly A we studied in the presence of Ca2+ ions with 10(-3)M Na+ in the solution. At concentrations lower than 10(-3)M Ca2+, the ions bind to phosphate groups of the single helical polymer, thus increasing its degree of helicity. At higher concentrations, the ions start binding to the bases of poly A, producing aggregates whose effective radius, as found with an electric microscope, is not more than 10(2) A. These particles stack to form aggregates of an order-of-magnitude higher size. The mutual orientation of bases in the poly A aggregates is of a high degree of order. The calculation of concentration dependences of Ca2+-poly A binding constants shows that this process is cooperative.

Calcium↗