[Kinetics of ligand binding to nucleic acids at random fillings].

Ligand binding with nucleic acids is described in frames of the theory of random processes. It is shown that the probabilistic description of binding of a ligand to nucleic acid allows one to describe not only the kinetics of changes in the number of bound ligands at arbitrary fillings but also to calculate stationary values of the number of bound ligands and its dispersion. A general analysis of absorption isotherms and the kinetics of ligand binding with nucleic acids allows one to determine the rate constants of formation and decomposition of the ligand-nucleic acid complex. A comparison of the results obtained with the case of low fillings is conducted.

[Modifying action of Mn(II) chelate with ethyl ester of salicylydene tyrosine on some biophysical parameters of erythrocyte membranes of the irradiated organism]. / Modifitsiruiushchee deistvie khelata Mn(II) s étilovym éfirom salitsiliden-tirozina na nekotorye biofizicheskie parametry éritrotsitarnykh membran obluchennogo organizma.

The presentation summarizes the results of studies on radioprotective activity of newly synthesized Mn(II) chelate with ethyl ester of salicylydene D,L-tyrosine, basing on the evaluation of its membrane-protective effects, revealed at different periods post the exposure of the organism to ionizing radiation. It was revealed that the administration of the compound into the animal organism before the radiation exposure (gamma-irradiation of 60Co at a dose level of 4.8 Gy) produced correcting action on structure-functional properties of erythrocyte membrane of irradiated rats: the excessive activation of lipid peroxidation of erythrocyte membranes was inhibited, the passive permeability of erythrocytes for K+ ions was normalized, the deformity and membrane potential of erythrocytes according to hydrogen-chlorine gradient were recovered.

[Membrane potential before and after deep freezing of Escherichia coli in the presence of dimethyl sulfoxide and diethyl sulfoxide]. / Membrannyi potentsial do i posle glubokogo zamorazhivaniia Escherichia coli v prisutstvii dimetilsul'foksida i diétilsul'foksida.

It was shown by the method of penetrating tetraphenylphosphonium cations that low-temperature freezing (-196 degrees C) of Escherichia coli leads to a sharp decrease (from 198 to 85 mV) in membrane potential. Incubation of bacteria in a medium containing dimethyl sulfoxide and diethyl sulfoxide as cryoprotectors results in a reduction of the potential by 16 and 27 mV, respectively. It was also shown that diethyl sulfoxide is more effective in maintaining the membrane potential after freezing--thawing than dimethyl sulfoxide.

The influence of external environment fluctuations on the signal formation of microbiosensors.

This part of theoretical analysis describes the fluctuations of output signal of microbiosensors when the number of accessible molecular recognition elements (enzymes, receptors, antibodies, etc.) fluctuated under external environmental influences. The mean electric current, dispersion correlating function, as well as spectral density of output current fluctuation are analyzed, and it is shown that a comparison of theoretically calculated mean current and correlation function with experimental data allow a determination of the kinetic parameters of substrate binding reaction with the molecular recognition element of biosensor.

[A novel method of analysis of ligand-polynucleotide adsorption isotherms]. / Novyi metod analiza izoterm adsorbtsii ligandov s polinukleotidami.

The adsorption of ethidium bromide on the synthetic double-stranded polyribonucleotide poly(G)poly(C) was investigated by adsorption spectroscopy. The adsorption isotherms were analyzed in the framework of the Crothers-Gursky model. It was shown that adsorption parameters (e.g., binding constant) may also be determined from the analysis of dispersion of some bound molecules. In some cases this method may be more convenient.

[The surface membrane potential in a fluctuating medium]. / Poverkhnostnyi potentsial membrany v fluktuiruiushchei srede.

Fluctuations of the surface membrane potential due to adsorbtion and desorbtion of ions when environmental fluctuations generate a fluctuation in the number of adsorbtion sites were investigated. The correlation functions of surface charge density, surface potential and the spectral density of surface potential fluctuations were calculated. The characteristic features of these fluctuations were determined.

[Stochastic model of localized adsorption of particles on membranes]. / Stokhasticheskaia model' lokalizovannoi adsorbtsii chastits na membranakh.

A stochastic model of localized adsorption of particles on the membrane was constructed. In the model, the transitional processes were neglected, and adsorption was represented as a stationary Markov process. In the framework of this approach, stationary values of average numbers of particles, there dispersion, correlation function, and spectral density were estimated. It was shown that the comparison of theoretical and experimental correlation functions (or spectral density) enables one to obtain new information about the adsorption parameters, namely: formation and decomposition rate constants for a complex of an adsorbed particle with the absorption center.

Electromechanical stability of planar lipid membranes from bipolar lipids of the thermoacidophilic archebacterium Sulfolobus acidocaldarius.

Stable planar membranes have been obtained from the bipolar lipid glycerol dialkyl nonitol tetraether (GDNT) extracted from the thermoacidophilic archebacterium Sulfolobus acidocaldarius. The electric capacity Cm, the resistance Rm and tension sigma of these membranes were measured. The dependence of the bipolar lipid membranes mean life time tau 1 on voltage was investigated. It was shown that the irreversible electric breakdown of membranes from GDNT and usual phospholipids is due to the same mechanism, viz., due to formation of a hydrophilic pore with an overcritical radius. Under electric field the GDNT molecules take U-shape, and the polar headgroups of such molecules cover the pore's interior.

The influence of gangliosides on the hydrophilic pore edge line tension and monolayer fusion of lipid membranes.

It is shown that inclusion of gangliosides into planar phospholipid bilayers leads to an essential suppression of their monolayer fusion. In contrast to phospholipid lysoforms, the gangliosides do not cause an associative decrease of the specific energy of the hydrophilic pore edge determined in the experiments on the electrical breakdown of membranes. This phenomenon depends on the effective size of the polar headgroup of the gangliosides. It is supposed that the effect of gangliosides on the parameters mentioned is based on the fact that they have large hydrated polar headgroups which create steric hindrances, which prevent (i) the membranes to come into contact during monolayer fusion; (ii) the gangliosides to take part in hydrophilic pore formation.

[Effect of exposure to "stress" on the electrical properties of BLM]. / Vliianie "stressovykh" vozdeistvii na élektricheskie svoistva BLM.

The influence of high potential and hydrostatic pressure gradients on BLM has been studied. It has been found that short exposures of BLM to the above factors, which are nearly as strong as those rupturing BLM, often induce in the membrane unusual states characterized by drastic increase in the current fluctuations with simultaneous increase of its average value. The level of fluctuations and the average current on individual membranes subjected to intermittent exposures vary appreciably. Of greatest interest are the membranes for which the average current value is not much higher than the background level. Such membranes can fluctuate steadily for several hours without any appreciable change in their behavior. In these cases the minimum current value during fluctuations often corresponds to the background current. Usually the current fluctuations on membranes excited by potential or hydrostatic pressure gradients cease abruptly. The electrical properties of such membranes are virtually the same as those of the unstressed membranes. The qualitative studies of the influence of the solution composition and temperature showed that in the range 25--40 degrees C in different solutions the excitation effects of BLM from general lipids of brain and a lecithin-cholesterol mixture are qualitatively similar and resemble those due to some biologically active substances diminishing the mechanical stability of BLM. Some possible mechanisms of excitation of BLM exposed to stress factors are discussed.