Structural aspects of catalytic mechanisms of endonucleases and their binding to nucleic acids

Endonucleases (EC 3.1) are enzymes of the hydrolase class that catalyze the hydrolytic cleavage of deoxyribonucleic and ribonucleic acids at any region of the polynucleotide chain. Endonucleases are widely used both in biotechnological processes and in veterinary medicine as antiviral agents. Medical applications of endonucleases in human cancer therapy hold promise. The results of X-ray diffraction studies of the spatial organization of endonucleases and their complexes and the mechanism of their action are analyzed and generalized. An analysis of the structural studies of this class of enzymes showed that the specific binding of enzymes to nucleic acids is characterized by interactions with nitrogen bases and the nucleotide backbone, whereas the nonspecific binding of enzymes is generally characterized by interactions only with the nucleic-acid backbone. It should be taken into account that the specificity can be modulated by metal ions and certain low-molecular-weight organic compounds. To test the hypotheses about specific and nonspecific nucleic-acid-binding proteins, it is necessary to perform additional studies of atomic-resolution three-dimensional structures of enzyme-nucleic-acid complexes by methods of structural biology.     

Electrical and magnetic properties of nanodiamond and pyrocarbon composites

The electrical and magnetic properties of the nanodiamond composites comprising nanodiamond, pyrolytic carbon, and nanosized pores were studied. The composites are p-type semiconductors and their resistance decreases by 12 orders of magnitude as the pyrocarbon-to-diamond ratio γ increases from 0 to 80 wt %. Evidence for paramagnetic properties of the nanodiamond composites was obtained. The observed properties are explained by increased concentration of surface Tamm states. The paramagnetic properties are explained in terms of the electron spins localized on the nanodiamond surface in the composite.     

Magnetization Anisotropy in the Textured Bi-2223 HTS in Strong Magnetic Fields

Physics of the Solid State - The origin of the low magnetization anisotropy of the textured bulk samples consisting of highly anisotropic (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) high-temperature...     

Mechanism of erythrocyte aggregation enhancement by ultrasonic field

Effect of a standing ultrasonic wave on the spontaneous and induced (specific, immune) processes of erythrocyte aggregation is studied in vitro on the basis of the data obtained from the elastic scattering of light. The effect of the time of ultrasonic action and the concentration of the initial reagents on the enhancement of these processes is analyzed. An approximate theoretical model is developed to describe the mechanism of the enhancement of erythrocyte aggregation by an ultrasonic field and the observation of the process of interest by the turbidimetric optical method. The model provides a good agreement between theory and experiment. The results of the study are used to derive recommendations as to how to increase the resolving power of the turbidimetric method of immunoanalysis with the aid of ultrasound.     

Andreev reflection and experimental temperature dependences of the critical current in heterogeneous high-temperature superconductors (polycrystals and related composites)

The temperature dependences of the critical current of Y_3/4Lu_1/4Ba₂Cu₃O₇ polycrystalline high-temperature superconductors subjected to annealing for different times and those of Y_3/4Lu_1/4Ba₂Cu₃O₇ + BaPbO₃ composites were measured. The results obtained were analyzed in terms of the Gunsenheimer-Schüssler-Kümmler theory considering the Andreev reflection of carriers in a “superconductor-normal metal-superconductor” (S-N-S) junction. Good agreement between the experimental and theoretical temperature dependences of the critical current over a wide temperature range for polycrystals with both natural and artificially created boundaries (composites) made it possible to estimate the effective length of grain boundaries in the high-temperature superconductors. It was revealed that the critical current density measured at 4.2 K is an exponential function of the length of grain boundaries in samples of both types.     

On the two-phase magnetic state in a CuxZn1−x Cr2Se4 cation-substituted chalcogenide spinel

The region of the concentration magnetic phase transition in a Cu_xZn_1?x Cr₂Se₄ chalcogenide spinel in which the substituted ion concentration x smoothly varies from 0.1 to 0.2 with a step of 0.02 is thoroughly investigated. An anomalous behavior of the Curie temperature is observed. This anomaly is associated with the nucleation of ferromagnetically ordered microregions in the vicinity of Cr ions with an intermediate valence and subsequent long-range magnetic ordering at a critical Cu concentration in the range 0.12<x _c <0.14. The possible coexistence of ferro-and antiferromagnetism in the same temperature range is revealed.     

Low-temperature metal-insuslator transition and magnetic properties in the VxMn1−x S disordered system

A study of the structure and electrical and magnetic properties of the V_xMn_1−x S disordered system is reported. The existence of a low-temperature metal-insulator transition for Fermi-glass 0.4<x<0.5 compositions in paramagnetic phase, which is accompanied by a change in the structure and magnetic properties, has been established. An analysis of the magnetic properties permits a conjecture that current carriers become delocalized in these solid solutions at the metal-insulator transition temperature to form small ferromagnetically ordered regions (ferrons). Fiz. Tverd. Tela (St. Petersburg) 39, 1428–1431 (August 1997)