Formation of the left-handed helix during simultaneous treatment of poly[d(GC)] with bis-netropsin and Zn(II) ions

It has been found that the effect of AT-specific ligand and Zn2+ on GC-alternating polymer brings about transfer of the latter into Z-conformation.     

DNA and RNA strand scission by copper, zinc and manganese superoxide dismutases

Copper/zinc (Cu/ZnSOD) and manganese (MnSOD) superoxide dismutases which catalyze the dismutation of toxic superoxide anion, O _inf2 ^sup– , to O₂ and H₂O₂, play a major role in protecting cells from toxicity of oxidative stress. However, cells overexpressing either form of the enzyme show signs of toxicity, suggesting that too much SOD may he injurious to the cell. To elucidate the possible mechanism of this cytotoxicity, the effect of SOD on DNA and RNA strand scission was studied. High purity preparations of Cu/ZnSOD and MnSOD were tested in an in vitro assay in which DNA cleavage was measured by conversion of phage X174 supercoiled double-stranded DNA to open circular and linear forms. Both types of SOD were able to induce DNA strand scission generating single- and double-strand breaks in a process that required oxygen and the presence of fully active enzyme. The DNA strand scission could be prevented by specific anti-SOD antibodies added directly or used for immunodepletion of SOD. Requirement for oxygen and the effect of Fe(II) and Fe(III) ions suggest that cleavage of DNA may be in part mediated by hydroxyl radicals formed in Fenton-type reactions where enzyme-bound transition metals serve as a catalyst by first being reduced by superoxide and then oxidized by H₂O₂. Another mechanism was probably operative in this system, since in the presence of magnesium DNA cleavage by SOD was oxygen independent and not affected by sodium cyanide. It is postulated that SOD, by having a similar structure to the active center of zinc-containing nucleases, is capable of exhibiting non-specific nuclease activity causing hydrolysis of the phosphodiester bonds of DNA and RNA. Both types of SOD were shown to effectively cleave RNA. These findings may help explain the origin of pathology of certain hereditary diseases genetically linked to Cu/ZnSOD gene.     

Results of irradiating chick embryos during incubation with very low doses of penetrating radiation

The weight of chick embryos and their organs increases and the mortality rate of embryos decreases under chronic gamma-irradiation during incubation with very low doses the dose-rate being 7.5 times as high as that of natural radiation background.     

Spectral manifestations of the effect of Zn2+ ions on DNA complexes with distmycin

Effect of low concentrations of metal bivalent ions on DNA-distamycin complexes was studied. It has been found that when adding small quantity of Zn2- ions the DNA-distamycin complex changes its cooperative properties. A small amount of heavy metal ions incorporated in DNA changes the DNA property to form complexes capable of stimulating the formation of structures of high organization. Thus under the effect of metal small additions both the structure of cellular processes and their regulation are irreversibly simplified, the phase of rest characterized by the maximal number of organization levels of the nuclear apparatus not being reached.     

Stimulating effect of very low doses of chronic gamma irradiation on the development of chick embryos

A study was made of the influence of chronic gamma-irradiation, with very low doses, of chick embryos during incubation on the dynamics of changes in the parameters characterizing the proliferative activity of cells. The original method is proposed for the analysis of these parameters and the results obtained by this method are discussed.