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Thermodynamic parameters of melting process (DeltaHm, Tm, DeltaTm) of calf thymus DNA, poly(dA)poly(dT) and poly(d(A-C)).poly(d(G-T)) were determined in the presence of various concentrations of TOEPyP(4) and its Zn complex. The investigated porphyrins caused serious stabilization of calf thymus DNA and poly poly(dA)poly(dT), but not poly(d(A-C))poly(d(G-T)). It was shown that TOEpyp(4) revealed GC specificity, it increased Tm of satellite fraction by 24 degrees C, but ZnTOEpyp(4), on the contrary, predominantly bound with AT-rich sites and increased DNA main stage Tm by 18 degrees C, and Tm of poly(dA)poly(dT) increased by 40 degrees C, in comparison with the same polymers without porphyrin. ZnTOEpyp(4) binds with DNA and poly(dA)poly(dT) in two modes--strong and weak ones. In the range of r from 0.005 to 0.08 both modes were fulfilled, and in the range of r from 0.165 to 0.25 only one mode--strong binding--took place. The weak binding is characterized with shifting of Tm by some grades, and for the strong binding Tm shifts by approximately 30-40 degrees C. Invariability of DeltaHm of DNA and poly(dA)poly(dT), and sharp increase of Tm in the range of r from 0.08 to 0.25 for thymus DNA and 0.01-0.2 for poly(dA)poly(dT) we interpret as entropic character of these complexes melting. It was suggested that this entropic character of melting is connected with forcing out of H2O molecules from AT sites by ZnTOEpyp(4) and with formation of outside stacking at the sites of binding. Four-fold decrease of calf thymus DNA melting range width DeltaTm caused by increase of added ZnTOEpyp(4) concentration is explained by rapprochement of AT and GC pairs thermal stability, and it is in agreement with a well-known dependence, according to which DeltaT approximately TGC-TAT for DNA obtained from higher organisms (L. V. Berestetskaya, M. D. Frank-Kamenetskii, and Yu. S. Lazurkin. Biopolymers 13, 193-205 (1974)). Poly (d(A-C))poly(d(G-T)) in the presence of ZnTOEpyp(4) gives only one mode of weak binding. The conclusion is that binding of ZnTOEpyp(4) with DNA depends on its nucleotide sequence.

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CD spectra of (DNA-TOEPyP4) + ZnTOEPyP4, (DNA-ZnTOEPyP4) + TOEPyP4, and DNA + (TOEPyP4-ZnTOEPyP4) complexes have been studied. It is shown that CD spectra of these triple complexes significantly differ from the DNA-TOEPyP4 and DNA-ZnTOEPyP4 double complex spectra, and they are not sum of these double complexes. Especially some strong differences in CD spectra of the triple and double complexes were observed when both porphyrins were added simultaneously into the DNA solution. In this case, ZnTOEPyP4 revealed a dominant influence on CD spectrum form. Zn-porphyrin also caused a strong intensity of positive band at 416 nm and a negative band at 437 nm when it was added into solution containing the DNA-TOEPyP4 complex. On the basis of obtained data, it was supposed that the observed significant changes in CD spectra of triple complexes were connected to an altered DNA conformation initiated by intercalation of porphyrin TOEPyP4 into GC-rich sites. The melting process analysis of the double complexes was carried out. The mechanisms of individual and joint influence of the porphyrins on DNA, and influence of binding modes on stability of these complexes are also discussed.

Conformation changes of calf thymus DNA induced by nanomole concentrations of Co(+2) and TOEPyP4 and influence of this ion on porphyrin binding mode with DNA duplex were studied at two NaCl concentrations (10 and 100 mM) using circular dichroism spectroscopy and absorption data. It was shown that addition of 85 nM Co(+2) into TOEPyP4/DNAb.p. = .015 solution caused an immediate change of the intercalative binding mode of porphyrin to external binding modes at low ionic strengths (10 mM NaCl). Increase of Co(+2) concentration from 165 to 650 nM caused a cooperative transition of DNA from B form to C-like conformation. Similar changes in binding mode and DNA conformation were observed at 100 mM NaCl, but they took place at higher concentrations of Co(+2) ions. Incubation of TOEPyP4/DNAb.p. = .015 in the presence of nanomole concentrations of Co(+2) ions at 36.6 °C showed a transition of DNA-B form into Z-like conformation. Maximal percent of Z-like DNA was observed when the incubation time was from 6 to 8 h. Longer incubation times of [DNA-TOEPyP4]+Co(+2) complexes caused a considerable recovery of CD spectra in UV region and a strong decrease in absorption at 260 nm. Here, we discuss some mechanisms of transition from B-DNA to C- and Z-like conformations.

Gerontology research carried out in different scientific centers of Georgia follows the basic directions of most work in this field: epidemiology, investigation of the mechanisms of aging, and finding ways to prevent senile pathologies and to prolong life. The genealogy and epidemiology of long-living peaple have been studied in areas with high occurrence of these people by considering the sex ratio and social status of the long-living, the influence of environmental factors, and the development of senile pathologies. According to the centrosome (centriole) model of aging, the centrosomes and the cytoskeleton, important structures in cellular differentiation and morphogenesis, may be involved in the initiation of the replication senescence mechanism. Our analysis of genetic studies shows that progressive chromosome heterochromatinization (condensation of eu- and heterochromatin regions) occurs in aging. Decreases in the repair processes and increases in the frequency of chromosome aberrations during aging are secondary to this progressive chromosome heterochromatinization. Chromosome heterochromatinization is a key factor in aging but may be reversible under the influence of bioregulators, some chemical substances, and heavy metal salts. The study of chromosome heterochromatinization may provide clues to the potential for prolonging the human lifespan.

It is known that at low concentrations of TMPyP4, this porphyrin predominantly intercalates between GC pairs at GC-rich sites of duplex DNA and G-quadruplexes of various constructions, and stabilizes these structures. However, there are still some arguable suggestions about the exact binding sites and modes of TMPyP4 to GC-rich regions of DNA in case of helation of divalent ions with help of the porphrin, which makes porphyrin structure asymmetric. We examined TOEPyP4-analogue of TMPyP4-and studied interaction of TOEPyP4 into the calf thymus DNA at presence of nanomole concentrations of one of the most important microelements in cell vital function-Zn ion. On the basis of CD and absorption spectra of the DNA-TOEPyP4 mixture, it was determined that nanomole concentrations of Zn ions changed porphyrin intercalative binding mode to some external binding modes, which initiated transition of the canonic B conformation of DNA into C-like conformation, and incubation of the (DNA-TOEP4) + Zn mixture at 37˚C caused B-Z-like transition, but no transition was observed for the DNA-TOEPyP4 mixture. In particular, at 10 mM·NaCl, TOEPyP4/DNA = 0.02, the binding mode change was observed in the concentration range from 150 to 300 nM·Zn, and the B-C-like transition occurred from 150 to 600 nM·Zn. The B-Z transition at TOEPyP4/DNA = 0.015, Zn/DNA = 0.015, NaCI 10 mM, T = 37˚C was observed within incubation time interval from 0.3 to 20 hours, and maximal percents of Z-like form was seen when incubation time interval was from 5 to 6 hours.

ЭНЕРГЕТИКА ПЕРЕХОДОВ В-Z-И Z-КЛУБОК В ВОДНЫХ РАСТВОРАХ ПОЛИ(dG-dC)* С использованием методов дифференциальной сканирующей калориметрии (ДСК), кругового дихроизма (КД) и У Φ-спектро фотометрии исследовали переходы В-Z-и Zспираль-клубок в поли (dG-dC). При 76 °С наблюдался обратимый переход, идентифицированный как В-Z-nepexod. При 97 °С был зафиксирован гораздо более интенсивный по теплопоглощению переход Z-спираль-клубок. Рассчитаны термодинамические параметры этих переходов.