Subterahertz chaos generation by coupling a superlattice to a linear resonator.

We investigate the effects of a linear resonator on the high-frequency dynamics of electrons in devices exhibiting negative differential conductance. We show that the resonator strongly affects both the dc and ac transport characteristics of the device, inducing quasiperiodic and high-frequency chaotic current oscillations. The theoretical findings are confirmed by experimental measurements of a GaAs/AlAs miniband semiconductor superlattice coupled to a linear microstrip resonator. Our results are applicable to other active solid state devices and provide a generic approach for developing modern chaos-based high-frequency technologies including broadband chaotic wireless communication and superfast random-number generation.

[Sodium specificity of the effect of cyclic nucleotides on the conductance of cytoplasmic membranes of the photoreceptor]. / Natrievaia spetsifichnost' vliianiia tsiklicheskikh nukleotidov na provodimost' tsitoplazmaticheskoi membrany fotoretseptora.

The effect of cyclic nucleotides (3',5'-cAMP and 3',5'-cGMP) on the membrane of the retina rod outer segment under intracellular dialysis conditions was shown to possess sodium specificity, its value in the medium with normal Na+ content being 4-20 times above that in sodium free solution. The results obtained permit a conclusion that the effect observed is due to the increased conductance of the cytoplasmic membrane of the outer segment and support the assumption concerning the mediator role of cyclic nucleotides in the photoreceptor act.

[Conductance of cytoplasmic membrane of photoreceptors by the method of intracellular dialysis]. / Izuchenie provodimosti tsitoplazmaticheskoi membrany fotoretseptora metodom vnutrikletochnogo dializa.

To clear up the effect of agents proposed as a mediator in the phototransduction process on the rod outer segment cytoplasmic membrane a technique based on the intracellular dialysis method was developed. It was shown that in the presence of nucleoside-triphosphates 3',5'-cGMP increased cytoplasmic membrane sodium conductance of dialyzed rod outer segment by 1-4 nS. The dependence of the effect amplitude on the cyclic nucleotides concentrations was obtained. It is suggested that the conductance changes observed are due to the action of cyclic nucleotide dependent protein kinase on the rod outer segment plasma membrane.

Use of a reverse micelle system for study of oligomeric structure of NAD+-reducing hydrogenase from Ralstonia eutropha H16.

Inclusion of an oligomeric enzyme, NAD+-dependent hydrogenase from the hydrogen-oxidizing bacterium Ralstonia eutropha, into a system of reverse micelles of different sizes resulted in its dissociation into catalytically active heterodimers and subunits, which were characterized in reactions with various substrates. It was found that: 1) the native tetrameric form of this enzyme catalyzes all types of studied reactions; 2) hydrogenase dimer, HoxHY, is a minimal structural unit catalyzing hydrogenase reaction with an artificial electron donor, reduced methyl viologen; 3) all structural fragments containing FMN and NAD+/NADH-binding sites exhibit catalytic activity in diaphorase reactions with one- and two-electron acceptors; 4) small subunits, HoxY and HoxU also exhibit activity in diaphorase reactions with artificial acceptors. These results can be considered as indirect evidence that the second FMN molecule may be associated with one of the small subunits (HoxY or HoxU) of the hydrogenase from R. eutropha.