Scattering properties of carbon nanotube antennas

The boundary problem of diffraction and excitation of system of nanotubes-vibrators was reduced to solution of the integral equation (IE) with logarithmic kernel. After regularization the IEs were solved by means of collocation method considering th current’s behaviour at the vibrator's endings. The existence of resonances in the frequency range 0.1-1.0 THz was shown

Puromycin reaction for the A site-bound peptidyl-tRNA

AbstractAcPhe2-tRNAPhe synthesized in 70S ribosomes after consecutive binding of AcPhe-tRNAPhe at the P sites and EF-Tu-directed binding of Phe-tRNAPhe at the A sites is able to react quantitatively with puromycin in the absence of EF-G. A detailed study of the kinetics of the puromycin reaction, its comparison with that of spontaneous translocation, the use of antibiotic viomycin as an effective inhibitor of spontaneous translocation revealed that, besides spontaneous translocation, this peptidyl-tRNA could react with puromycin being located at the A site. This leads to the conclusion that the transpeptidation reaction per se triggers conformational changes in the ribosomal complex bringing the 3′-end of a newly synthesized peptidyl-tRNA nearer to the peptidyl-site of the peptidyltransferase center. This is detected functionally as the ability of such an A site bound peptidyl-tRNA to react with puromycin. This reaction is highly pronounced at elevated (25°C) temperature but can be hardly detected at 0°C

Mechanism of codon-anticodon interaction in ribosomes. Direct functional evidence that isolated 30S subunits contain two codon-specific binding sites for transfer RNA.

30S subunits were isolated capable to bind simultaneously two molecules of Phe-tRNAPhe (or N-Acetyl-Phe-tRNAPhe), both poly(U) dependent. The site with higher affinity to tRNA was identified as P site. tRNA binding to this site was not inhibited by low concentrations of tetracycline (2 x 10(-5)M) and, on the other hand, N-Acetyl-Phe-tRNAPhe, initially prebound to the 30S.poly(U) complex in the presence of tetracycline, reacted with puromycin quantitatively after addition of 50S subunits. The site with lower affinity to tRNA revealed features of the A site: tetracycline fully inhibited the binding of both Phe-tRNAPhe and N-Acetyl-Phe-tRNAPhe. Binding of two molecules of Phe-tRNAPhe to the 30S.poly(U) complex followed by the addition of 50S subunits resulted in the formation of (Phe)2-tRNAPhe in 75-90% of the reassociated 70S ribosomes. These results prove that isolated 30S subunits contain two physically distinct centers for the binding of specific aminoacyl- (or peptidyl-) tRNA. Addition of 50S subunits results in the formation of whole 70S ribosomes with usual donor and acceptor sites

Comparative study of the interaction of polyuridylic acid with 30S subunits and 70S ribosomes of Escherichia coli.

Fractionated polyuridylic acid with an average chain length of 55 nucleotides forms binary complexes with 30S subunits with a stoichiometry of I:I. These complexes are heterogeneous in stability. The more stable one is characterized by an association constant K2 - 5.5xI09 M-I, and the less stable-by KI = I06xM-I, at 20 mM Mg2+, 200 mM NH4(+) and 0 degrees C. The main reason for this heterogeneity is the presence or absence of the ribosomal protein SI in the presence or absence of the ribosomal protein SI in the subunits. Decrease of Mg2+ concentration down to 5 mM hardly changes the K2 values but reduction of the NH4(+) concentration to 50 mM results in a 25-fold increase of K2. Association constants K2 for the stable complex, i.e. in the presence of SI protein, were measured at different temperatures (0 - 30 degrees C) and the thermodynamic parameters of binding (delta H degrees, delta S degrees, delta G degrees) were determined. Analogous experiments were made with 70S ribosomes. K2 values as well as delta H degrees, delta S degrees, delta G degrees appeared the same both for 30S and 70S ribosomes in all conditions examined. This is strong evidence that the 50S subunits do not contribute to the interaction of poly(U) with the complete 70S ribosomes

Electrodynamic analysis of nanoscale antennas of millimeter and optical bands

Electrodynamic models and radiophysical properties of carbon nanotubes – vibrators (isolated on the substrate lattices), metallic optical antennas and optical antennas, formed from ZnO nanorods coated with metal films were developed and investigated. The models are based on numerically-analytical solution of integro-differential equations describing the diffraction of electromagnetic waves on impedance and dielectric bodies. Using the integral representations of the kernels of integro-differential equations allowed to overcome the difficulties of solution, associated with the singularity of kernels and to reduce the computation time for an order

Synthesis, Electrical and Magnetic Properties of Composites Copper Iodide/Magnetite-Polychlorotrifluoroethylene

The structural, magnetic and electrophysical properties of composites based on nanosized magnetite chemically modified of copper iodide and polychlortrifluoroethylene have been studied at temperatures 298 – 450 K and CuI concentrations of from 0 to 0,58 volume. It has been found the optimal volume content of copper iodide ( 0,4) in the composites CuI/Fe3O4, when the interfacial interaction shows most intensively and maximum values electrical parameters take place. The value of the coercive force of nanocomposites CuI/Fe3O4 increases with increasing content copper iodide. It was shown that polymer composites containing CuI/Fe3O4, have higher values of real and imaginary components of complex permittivity and conductivity compared with a system that contains only copper iodide. Keywords: magnetite, copper iodide, nanocomposites, specific magnetization, interfacial interaction.</span

Purpuromycin: a new inhibitor of tRNA aminoacylation

Purpuromycin, an antibiotic produced by Actinoplanes ianthinogenes, had been reported previously to inhibit protein synthesis. In the present report, we demonstrate that the mechanism of action of this antibiotic is quite novel in that it binds with fairly high affinity to all tRNAs, inhibiting their acceptor capacity. Although more than one molecule of purpuromycin is bound to each tRNA molecule, the inhibitory activity of this antibiotic was found to be selective for the tRNA acceptor function; in fact, after the aminoacylation step, purpuromycin was found to affect none of the other tested functions of tRNA (interaction with the ribosomal P- and A-sites and interaction with translation factors). Accordingly, purpuromycin was found to inhibit protein synthesis only when translation depended on the aminoacylation of tRNA and not when the system was supplemented with pre-formed aminoacyl-tRNAs. Because purpuromycin did not interfere with the ATP-PPi exchange reaction of the synthetase or with the initial interaction of the enzyme with its tRNA substrate, the basis for the inhibition of aminoacylation is presumably the formation of a nonproductive synthetase-tRNA complex in the presence of purpuromycin in which the tRNA is unable to be charged with the corresponding amino acid