Denaturation of mouse satellite DNA upon melting of chromatin in solution

The denaturation of mouse satellite DNA upon melting of chromatin in solution of low ionic strength has been studied. A procedure for preparation of partially denaturated chromatin was developed which enabled the isolation of double-stranded (non-denatured) DNA sequences according to their thermal stability in chromatin. The content of mouse satellite DNA in these DNA sequences was determined by hybridization with RNA, complementary to satellite DNA in order to find the temperature interval of denaturation of satellite DNA. It was found that the melting temperature of satellite DNA in chromatin was lower than that of the total DNA. The results are discussed in relation to previously reported anomalous behaviour of satellite DNA upon melting of chromatin on hydroxyapatite.     

Denaturation of mouse satellite and ribosomal DNA during hydroxyapatite thermal chromatography of chromatin

Mouse DNA and chromatin were melted on hydroxyapatite and the denaturation profiles of ribosomal and satellite DNAs were followed by hybridization with their complementary RNAs. Neither ribosomal nor bulk DNA had significantly different melting profiles in chromatin as compared to DNA. However, most of satellite DNA eluted at higher temperature from chromatin than from purified DNA. One explanation for the higher melting temperature of mouse satellite DNA in chromatin suggests that the complex between this particular DNA component and at least some proteins in chromatin is more stable than the average DNA-protein interaction.     

New Pyrimidine Cyclonucleosides with Hydrogenated Aglycones: Synthesis and X-Ray Structures

Abstract

Acid catalysed transformations of (6S)-6,5′-anhydro-6-hydroxy-1-(2′,3′-O-isopropylidene-β-D-ribofuranosyl)hexahydropyrimidine-2-thione are studied. (6R)-6,2′-anhydro-6-hydroxy-1-(α-D-ribofuranosyl)hexahydropyrimidine-2-thione was formed as a thermodynamically stable product. Two intermediates, (6S)-6,5′-anhydro-6-hydroxy-1-(β-D-ribofuranosyl)hexahydropyrimidine-2-thione and 6-hydroxy-1-(D-ribosyl)hexahydropyrimidine-2-thione and products of cleavage of glycosidic bond were identified in the reaction mixtures. Results of X-ray structural determination of the synthesised nucleosides are presented.     

Effect of ethanol on functional properties of the human hemoglobin molecule

The effect of ethanol on the oxygenation of hemoglobin was studied by kinetic absorption spectroscopy. It was found that the efficiency of oxygen geminate rebinding decreased upon ethanol addition. At ethanol concentrations up to 4.5 M, its influence on the structure and functional properties of the hemoglobin molecule is determined by changes in the bulk dielectric constant of solution. The decrease in the rate constant of the bimolecular stage of rebinding k'4 was caused by an increase in the viscosity of solution, with k'4 being approximately 1/eta 0.5. Upon oxidation of hemoglobin to hemichrome initiated by ethanol, dramatic conformational changes in the region of the heme pocket took place. They lead to a more than twofold increase in the efficiency of exit of oxygen molecules from the protein matrix to the solution after photodissociation.     

Stilbenoids from the stem of Gnetum latifolium (Gnetaceae)

An acetone extract of the stem of Gnetum latifolium Blume afforded the stilbene trimer (latifolol) together with five known stilbenoids (gnetin E, gnetin D, gnetin C, (-)epsilon -viniferin and resveratrol). Their structures were elucidated on the basis of spectral evidence, in particular by using 2D NMR methods.     

Isoflavone genistein-8-c-glycoside prevents the oxidative damages in structure and function of rat liver microsomal membranes

Bioflavonoids (polyhydroxyphenols) are ubiquitous components of plants, fruits and vegetables; these compounds are efficient scavengers of free oxygen radicals and peroxides. The aim of this study was to investigate the antioxidant and radioprotective effects of genistein-8-C-glicoside (G8CG), an isoflavone, isolated from the flowers of Lipinus luteusl L. G8CG prevents dose-dependently the destruction of the cytochrome P-450 and its conversion to an inactive form cytochrome P-420, inhibits membrane lipid peroxidation and membrane SH-group oxidation in isolated rat liver microsomal membranes under tert-butylhydroperoxide-induced oxidative stress. Single whole-body gamma-irradiation (1 Gy) of rats results in blood plasma and liver microsomal membrane lipid peroxidation, impairments of microsomal membrane structure and function. Rat treatment with G8CG (75 mg/kg) developed the clear protective effect, stabilized membrane structure and improved the parameters of the monooxygenase function. We can conclude that G8CG can be used as antioxidant and radioprotective agent.     

Parameters of interaction of sodium dodecyl sulfate with human hemoglobin

It was shown that sodium dodecyl sulfate at concentrations not exceeding the critical micelle concentrations (0-1.9 mM) induced the conversion of oxy- and methemoglobin but not deoxyhemoglobin to hemichrome. The concentration dependences of hemichrome formation were represented as Hill plots, and the parameters of detergent binding were estimated. OxyHb in 20 mM potassium-phosphate buffer, pH 6.8, has two groups of binding sites: the first group is characterized by the Hill constant n1 = 2 and the concentration of half saturation [SDS]50 = 0.8 mM, and the second group is characterized by the Hill constant n2 = 8 and [SDS]50 = 0.9 mM. In the case of metHb one group of binding sites with the Hill constant n = 2 and half saturation concentration [SDS]50 = 0.2 mM was observed. An increase in environmental pH to 7.9 decreased the affinity of Hb for SDS. It is suggested that primary binding sites for SDS in oxyHb coincide with the anion-binding center of the Hb molecule. The interaction of the detergent with these binding sites induced a structural transition of the hemoprotein molecule. As a result of this transition, secondary binding sites were exposed. In a model system (hemin--imidazole in ethanol solution), the enthalpy of the transition of hemin from a high-spin to a low-spin state was estimated to be 47 +/- 7 kJ/mol.     

Native HMGB1 protein inhibits repair of cisplatin-damaged nucleosomes in vitro

The high mobility group box (HMGB) 1 protein, one of the most abundant nuclear non-histone proteins has been known for its inhibitory effect on repair of DNA damaged by the antitumor drug cisplatin. Here, we report the first results that link HMGB1 to repair of cisplatin-treated DNA at nucleosome level. Experiments were carried out with three types of reconstituted nucleosomes strongly positioned on the damaged DNA: linker DNA containing nucleosomes (centrally and end-positioned) and core particles. The highest repair synthesis was registered with end-positioned nucleosomes, two and three times more efficient than that with centrally positioned nucleosomes and core particles, respectively. HMGB1 inhibited repair of linker DNA containing nucleosomes more efficiently than that of core particles. Just the opposite was the effect of the in vivo acetylated HMGB1: stronger repair inhibition was obtained with core particles. No inhibition was observed with HMGB1 lacking the acidic tail. Binding of HMGB1 proteins to different nucleosomes was also analysed. HMGB1 bound preferentially to damage nucleosomes containing linker DNA, while the binding of the acetylated protein was linker independent. We show that both the repair of cisplatin-damaged nucleosomes and its inhibition by HMGB1 are nucleosome position-dependent events which are accomplished via the acidic tail and modulated by acetylation.     

2,3-Butanedione monoxime does not protect cardiomyocytes under oxidative stress

Heart muscle ischemia-reperfusion provokes a pronounced cardiomyocyte oxidative stress. In the present study, we examined a possible protective effect of the cardioprotective drug, 2,3-butanedione monoxime (BDM), on the cultured neonatal cardiac myocytes exposed to oxidative stress induced by hypochlorous acid (HOCl), that may be formed by activated polymorphonuclear neutrophils in myocardium ischemic-reperfusion areas, and a useful model oxidant, tert-butyl hydroperoxide (tBHP). Using isolated rat cardiomyocytes substantial cytotoxicity of HOCl and tBHP was demonstrated: The concentrations of HOCl and tBHP causing a 50% decrease of cardiomyocyte cell viability were estimated to be 55 +/- 5 microM and 36 +/- 6 microM, respectively. The cell viability measured immediately after the tBHP oxidative treatment was significantly higher than that measured after 22 h of cell post-incubation in a fresh culture medium. This showed delayed cell death after removing tBHP. Hypochlorous acid treatment of cardiomyocytes did not change cellular viability during the cellular post-incubation in a fresh medium. Even a long-term (22 h) incubation of oxidatively damaged cardiomyocytes with BDM (5 mM) added after the HOCl removal did not recover the viability of the HOCl-exposed cells. In the presence of BDM, the cytotoxicity of HOCl significantly increased probably due to a direct reaction of both compounds and toxic chlorinated derivative formation. 2,3-Butanedione monoxime (5 mM) did not reduce cytotoxicity of tBHP, either. Such well-known antioxidative agents as melatonin or glutathione considerably prevented oxidant-induced cell death in a concentration-dependent manner.