How adsorption influences DNA denaturation.

The thermally induced denaturation of DNA in the presence of an attractive solid surface is studied. The two strands of DNA are modeled via two coupled flexible chains without volume interactions. If the two strands are adsorbed on the surface, the denaturation phase transition disappears. Instead, there is a smooth crossover to a weakly naturated state. Our second conclusion is that even when the interstrand attraction alone is too weak for creating a naturated state at the given temperature and also when the surface-strand attraction alone is too weak for creating an adsorbed state, the combined effect of the two attractions can lead to a naturated and adsorbed state.

Observation of resonant diffusive radiation in random multilayered systems.

Diffusive radiation is a new type of radiation predicted to occur in randomly inhomogeneous media due to the multiple scattering of pseudophotons. This theoretical effect is now observed experimentally. The radiation is generated by the passage of electrons of energy 200 KeV-2.2 MeV through a random stack of films in the visible light region. The radiation intensity increases resonantly provided the Cerenkov condition is satisfied for the average dielectric constant of the medium. The observed angular dependence and electron resonance energy are in agreement with the theoretical predictions. These observations open a road to application of diffusive radiation in particle detection, astrophysics, soft-x-ray generation, etc.

Adhesion-induced DNA naturation.

DNA adsorption and naturation is modeled via two interacting flexible homopolymers coupled to a solid surface. DNA denatures if the entropy gain for unbinding the two strands overcomes the loss of binding energy. When adsorbed to a surface, the entropy gain is smaller than in the bulk, leading to a stronger binding and, upon neglecting self-avoidance, absence of a denatured phase. Now consider conditions where the binding potentials are too weak for naturation, and the surface potential too weak to adsorb single strands. In a variational approach it is shown that their combined action may lead to a naturated adsorbed phase. Conditions for the absence of naturation and adsorption are derived too. The phase diagram is constructed qualitatively.

Unzipping of DNA with correlated base sequence.

We consider force-induced unzipping transition for a heterogeneous DNA model with a correlated base sequence. Both finite-range and long-range correlated situations are considered. It is shown that finite-range correlations increase stability of DNA with respect to the external unzipping force. Due to long-range correlations the number of unzipped base pairs displays two widely different scenarios depending on the details of the base sequence: either there is no unzipping phase transition at all, or the transition is realized via a sequence of jumps with magnitude comparable to the size of the system. Both scenarios are different from the behavior of the average number of unzipped base pairs (non-self-averaging). The results can be relevant for explaining the biological purpose of correlated structures in DNA.

[New antioxidant factors secreted by the gastrointestinal tract]. / Novye antioksidantnye faktory, sekretiruemye zheludochno-kishechnym traktom.

It is shown, that the cells of gastric and small intestinal tissues synthesize the unidentified compounds, which suppress the peroxidation of lipids in the renal, hepatic and brain tissues. The gastric factor is thermostabile, while the intestinal factor is partially thermolabile. In case of gastrointestinal pathology the activity of these factors is reduced. It is supposed that these factors protote the common antioxidant system of the organism, increase its immunoreactivity and prevent from the action of the destroying factors.

[Biochemical bases of the anti-ulcer action of GABA and sodium oxybate]. / Biokhimicheskie osnovy protivoiazvennogo deistviia GAMK i natriia oksibutirata.

It was found that GABA and sodium hydroxybutyrate are capable to prevent gastric ulcers. While protecting the animals from experimental ulcers both the substances display an ability to increase the content of ATP in the gastric wall. ATP that prevents the occurrence of experimental gastric ulcers enhances 14-leucine incorporation into proteins of gastric tissues. It was demonstrated in experiments ulcer prevention that under the effect of 32P-ATP the content of phosphorylated proteins in gastric tissues rises more than 2-fold. This circumstances ensures the increased resistance of the gastric mucosa to the action of proteolytic enzymes. Enhancement of oxygen consumption by the tissues should be also regarded as one of the factors determining high resistance of the mucosa to proteolysis.