Fleas of the eastern Kyzyl Kum and their epizootic significance]

The fauna of fleas in the East Kisil-Kum includes 24 species. Different physicogeographic regions of sands are characterized by different spectra and number of species of fleas. The greatest share in collections is composed by Xenopsylla gerbilli caspica--the parasite of Rhombomys opimus. In autumn the other parasite of this rodent, Coptopsylla lamellifer, is a mass species. All the most significant and long changes in the number of these species are associated with changes in the density of their hosts' population. The most significant in epizootic respect is the flea X. gerbilli caspica from which about 50% of plague agent cultures were isolated.     

Optimization of the exposure of normal and transformed cell populations to phase-specific agents

Dynamic behavior of stem cells population of the "critical" tissue (normal population) and tumor cell population under periodic treatment with a phase-specific cytotoxic agent was considered. The results were used for optimization of anticancer chemotherapy. The schedules of treatment were found which provide a maximum rate of tumor-cell elimination for any given rate of the normal population size decrease. If the mean generation times of normal and tumor populations differ (which was stated for many tumors), usage of the optimal period markedly increases the selectivity of therapy, while application of other periods can result in selective elimination of the normal population. Problems concerned with practical realization of the proposed regimes are discussed.     

Effect of phosphorus on polymyxin B biosynthesis by B. polymyxa 1538 on media of varying makeup]

The effect of phosphorus on biosynthesis of polymyxin B by B. polymyxa 1538 was studied and its optimal concentration in the synthetic and two complex media was determined. Correlation between the culture growth and consumption of the main components, on the one hand, and concentration of phosphorus in the medium, on the other hand, was found. It was shown that the effect of phosphorus on biosynthesis of polymyxin B did not depend on the carbon source in the medium and aeration conditions.     

Three-dimensional structure of the nickel-containing hydrogenase from Thiocapsa roseopersicina.

The three-dimensional structure of the nickel-containing hydrogenase from Thiocapsa roseopersicina has been determined at a resolution of 2 nm in the plane and 4 nm in the vertical direction by electron microscopy and computerized image processing on microcrystals of the enzyme. The enzyme forms a large ring-shaped complex containing six each of the large (62-kDa) and small (26-kDa) subunits. The complex is very open, with six well-separated dumbbell-shaped masses surrounding a large cylindrical hole. Each dumbbell is interpreted as consisting of one large and one small subunit.     

Structural basis for the destabilization of F-actin by phosphate release following ATP hydrolysis.

The role of ATP hydrolysis in actin polymerization has been a puzzle, since it is known that polymer formation is possible without the ATPase activity and that the ATPase lags behind polymerization. We have used beryllium fluoride and G-ADP actin monomers to form F-ADP-BeF3- filaments that are a stable analog for either the ATP or the ADP-P(i) state. Electron microscopy and computed three-dimensional reconstruction have been used to compare this state to control actin, F-ADP, polymerized from G-ATP. We find, at a high degree of statistical significance, that subdomain-2 of the actin protomer in the ADP-BeF3- state is in a conformation very similar to that found in the atomic model for F-actin of Holmes and co-workers, but becomes disordered after the release of the phosphate. This breaks one of the longitudinal bonds in the filament, consistent with biochemical observations that phosphate release destabilizes F-actin. We have also found that lithium, which reduces the dissociation rate constant of actin filaments, induces a structural state indistinguishable from that of ADP-BeF3-. Further, in all states about ten C-terminal residues are displaced from the above mentioned model, but that the fit of the rest of the monomer is in excellent agreement, supporting the uniqueness of the solution they found and precluding a significantly different arrangement of the actin monomer in the filament.     

On the fine structure of rat liver ribosome small subunits

An optical averaging of rat liver ribosome small subunit images revealed seven strands with a mean diameter of about 50 Å. A tentative model of the 3D arrangement of the strands is suggested. An assumption is made that these strands are clusters of protein molecules arranged on the double-helical regions of RNA.     

Evaluation of the sanative action of rifampicin on the meningococcal carrier state]

The results of the epidemiological control experiment on the efficacy of rifampicin in sanation of meningococci carriers are presented. The preliminary study of rifampicin sensitivity of 41 freshly isolated nasopharyngeal meningococcal strains showed that the MIC of the drug for 63 per cent of the isolates was 0.04--0.1 gamma/ml. Sanation was performed for 2 days; 1.2 g of the drug was used during the treatment course. The results of examination of 91 meningococci carriers showed that 4 days after the sanation the specific weight of the persons isolating no meningococci was reliably higher in the experimental group than that in the control group. The coefficient of rifampicin efficiency was 70.8 per cent. 10 days after sanation the difference in the level of the carriers isolating no meningococci in the experimental and the control groups was statistically insignificant. Therefore, the carriers treated with the drug received temporary protection from the causative agent at an average for 1 week. Later on they could become carriers again. As a result of sanation no changes in the meningococcal sensitivity to rifampicin was observed.