Biocompatibility and applications of carbon nanotubes in medical nanorobots

The set of nanoelectromechanical systems (NEMS) based on relative motion of carbon nanotubes walls is proposed for use in medical nanorobots. This set includes electromechanical nanothermometer, jet nanoengine, nanosyringe (the last can be used simultaneously as nanoprobe for individual biological molecules and drug nanodeliver). Principal schemes of these NEMS are considered. Operational characteristics of nanothermometer are analyzed. The possible methods of these NEMS actuation are considered. The present-day progress in nanotechnology techniques which are necessary for assembling of NEMS under consideration is discussed. Biocompatibility of carbon nanotubes is analyzed in connection with perspectives of their application in nanomedicine.     

Changes in fatty acid composition of lipids in chloroplast membranes of tobacco plants during cold hardening

Changes in fatty acid composition of chloroplast membrane lipids were investigated using tobacco (Nicotiana tabacum L., cv. Samsun) plants subjected to cold hardening for 6 days at 8°C. Under optimal growing temperature (22°C), the lipids of thylakoid membranes were characterized by elevated content of 16:3n-3 and 18:3n-3 fatty acids (FA). Compared to the lipids of chloroplast envelope membranes, the thylakoid lipids were less rich in the content of saturated, mono- and diunsaturated FA. The relative content of unsaturated FA in chloroplast membranes increased substantially during cold hardening, which was mainly due to the accumulation of 18:3n-3 FA. It is concluded that the observed changes in FA composition of chloroplast lipids during cold hardening adjust the fluidity of these membranes to the level sufficient for functioning of tobacco photosynthetic apparatus, which is a prerequisite for accumulation of assimilates and allows the hardened tobacco plants to survive under conditions of hypothermia.     

Properties of bacterial and archaeal branched-chain amino acid aminotransferases

Branched-chain amino acid aminotransferases (BCATs) catalyze reversible stereoselective transamination of branched-chain amino acids (BCAAs) L-leucine, L-isoleucine, and L-valine. BCATs are the key enzymes of BCAA metab- olism in all organisms. The catalysis proceeds through the ping-pong mechanism with the assistance of the cofactor pyri- doxal 5′-phosphate (PLP). BCATs differ from other (S)-selective transaminases (TAs) in 3D-structure and organization of the PLP-binding domain. Unlike other (S)-selective TAs, BCATs belong to the PLP fold type IV and are characterized by the proton transfer on the re-face of PLP, in contrast to the si-specificity of proton transfer in fold type I (S)-selective TAs. Moreover, BCATs are the only (S)-selective enzymes within fold type IV TAs. Dual substrate recognition in BCATs is imple- mented via the “lock and key” mechanism without side-chain rearrangements of the active site residues. Another feature of the active site organization in BCATs is the binding of the substrate α-COOH group on the P-side of the active site near the PLP phosphate group. Close localization of two charged groups seems to increase the effectiveness of external aldimine for- mation in BCAT catalysis. In this review, the structure-function features and the substrate specificity of bacterial and archaeal BCATs are analyzed. These BCATs differ from eukaryotic ones in the wide substrate specificity, optimal tempera- ture, and reactivity toward pyruvate as the second substrate. The prospects of biotechnological application of BCATs in stereoselective synthesis are discussed.     

Plasma Decay in the Afterglow of High-Voltage Nanosecond Discharges in Unsaturated and Oxygenated Hydrocarbons

Results of experimental and theoretical study of plasma decay in the afterglow of high-voltage nanosecond discharges in gaseous ethylene and dimethyl ether at room temperature and pressures from 2 to 20 Torr are presented. Using a microwave interferometer, the time behavior of the electron density in the range from 2 × 10¹⁰ to 3 × 10¹² cm^–3 during plasma decay is investigated. By processing the experimental data, the effective coefficients of electron–ion recombination as functions of the gas pressure are obtained. It is found that these coefficients substantially exceed the recombination coefficients of simple hydrocarbon ions. This distinction, as well as the increase in the effective recombination coefficient with pressure, is explained by the formation of cluster ions in three-body collisions, which recombine with electrons more efficiently than simple molecular ions. The coefficients of three-body conversion of simple molecular ions into cluster ions in the plasmas of ethylene and dimethyl ether, as well as the coefficients of recombination of electrons with cluster ions in these gases, are determined by analyzing the experimental data.     

Overfishing in the Baltic Sea basin in Russia,its impact on the pearl mussel,and possibilities for the conservation of riverine ecosystems in conditions of high anthropogenic pressure

In recent studies nine populations of the freshwater pearl mussel have been described in the Baltic Sea basin in Russia. They are very scarce, although the condition of their habitats seems to be rather good. Overfishing of the host fish is a limiting factor for them. The number of salmon has decreased by at least 100 times over the past 200 years. Such a scale of decline tends to be hidden over time, and estimation of the normal conditions of the salmon–pearl mussel ecosystem becomes problematic. A significant increase in the number of salmon is necessary to prevent extinction of pearl mussels. Effective protected areas appear to be the only possibility for conservation of the pearl mussels and its host fish species.     

The isolation, preliminary structural studies, and physiological activity of water-soluble polysaccharides from the squeezed berries of the snowball treeViburnum opulus

Water-soluble polysaccharide fractions VO1–VO4 were isolated from the squeezed berries of the snowball tree (Viburnum opulus) by successive extraction with water at various temperatures and pH and with aqueous solutions of ammonium oxalate. These fractions were purified by ion-exchange chromatography on DEAE cellulose, and the homogeneity of the purified polysaccharides was determined by gel filtration on Sephacryl S-500. Acidic polysaccharides close to pectins in their sugar composition were found in all the extracts (fractions VO1-1, VO2-1, VO3-2, and VO4-2). Residues of galacturonic acid, galactose, arabinose, and (to a lesser extent) rhamnose are their main constituents. Neutral polysaccharides composed mainly of galactose and mannose residues were additionally found in fractions extracted with acidified water (pH 4.0) and with aqueous ammonium oxalate solutions. Partial acidic hydrolysis and digestion with pectinase of acidic polysaccharides indicated that their carbohydrate backbone consists of α-1,4-linked residues ofD-galacturonic acid. NMR spectra of acidic polysaccharides (fractions VO3-2 and VO3-3) confirmed this and demonstrated that their side oligosaccharide chains are composed of β-1,4-linked galactopyranose residues and of terminal and 2,5- and 3,5-substituted residues of α-arabinofuranose at a Gal : Ara ratio of 3 : 1. Some polysaccharides fromV. opulus were found to possess an immunostimulating activity: they enhance phagocytosis, in particular, the phagocytic index and the secretion of lysosomal enzymes with peritoneal macrophages. Calcium ions were found to be necessary for the appearance of the stimulating effect of acidic polysaccharides fromV. opulus.     

Subcellular localization and properties of glyoxylate cycle enzymes in the liver of rats with alloxan diabetes.

Key enzymes of the glyoxylate cycle (isocitrate lyase and malate synthetase) were found in the liver and kidney of rats suffering from alloxan diabetes. The activities of these enzymes in the liver were 0.080 and 0.0430 U/mg protein, respectively. Isocitrate lyase activity in the kidney was 0.030 U/mg protein, and that of the malate synthetase was 0.018 U/mg protein. Peroxisomal localization of the enzymes was shown. A novel malate dehydrogenase isoform was found in a liver of rats suffering from the alloxan diabetes. The isocitrate lyase was isolated by selective (NH4)2SO4 precipitation and DEAE-Toyopearl chromatography. The resulting enzyme preparation had specific activity 6.1 U/mg protein, corresponding to 76.25-fold purification with 32.6% yield. The isocitrate lyase was found to follow the Michaelis--Menten kinetic scheme (Km for isocitrate, 0.08 mM) and to be competitively inhibited by glucose 1-phosphate (Ki = 1. 25 mM), succinate (Ki = 1.75 mM), and citrate (Ki = 1.0 mM); the pH optimum of the enzyme was 7.5 in Tris-HCl buffer.     

Transposition of a DNA fragment flanked by two inverted Tn1 sequences

The 32 Md fragment (derived from plasmid RP4::Tn1) carrying the Km^r gene and flanked by two inverted Tn1 elements is capable of recA-independent translocation to other plasmids. We designated this new transposon Tn1755. In various crosses, frequencies of Tn1755 transposition to plasmids Co1B-R3, R15 and F′ColVBtrp varied from 2.5 to 90% of the frequencies of Tn1 transposition. Tn1755 can integrate into various sites of the recipient plasmids. We failed to observe transposition of another RP4::Tn1 fragment flanked by two opposingly oriented Tn1 transposons and harboring the Tc^r gene. Presumably, to form a new transposable structure, other features must also be of importance.     

Studies of the optical properties of laser plasmas produced by irradiating spherical targets

Results are presented from studies of the spectral characteristics of a glowing plasma object that forms behind a shock wave propagating in a background gas at a pressure of 1 Torr after laser irradiation of a spherical organic target in the MKV-4 device (a component of the Iskra-5 facility). The experimental data are compared to the results of calculations.