[Ion channels of various types induced in lipid membranes by gramicidin A derivatives carrying a cationic sequence at their C-termini].

The channel-forming activity of gramicidin A derivatives carrying positively charged amino acid sequences at their C-termini was studied on planar bilayer lipid membranes and liposomes. We showed previously that, at low concentrations, these peptides form classical cation-selective pores typical of gramicidin A, whereas, at high concentrations, they form large nonselective pores. The ability of the peptides to form nonselective pores, which was determined by the efflux of carboxyfluorescein, an organic dye, from liposomes, decreased substantially as the length of the gramicidin fragment in the series of cationic analogues was truncated. CD spectra showed that large pores are formed by peptides having both beta6.3 single-stranded and beta5.6 double-stranded helical conformations of the gramicidin fragment, with the C-terminal cationic sequence being extended. The dimerization of the peptides by the oxidation of the terminal cysteine promoted the formation of nonselective pores. It was shown that nonselective pores are not formed in membranes of erythrocytes, which may indicate a dependence of the channel-forming ability on the membrane type. The results may be of interest for the directed synthesis of peptides with antibacterial activity.

[The effect of the composition of phospholipid bilayer membranes on the steady state kinetic transfer of protons]. / Vliianie sostava bisloinoi fosfolipidnoi membrany na statsionarnuiu kinetiku perenosa protona.

When the hydrogen ion flux was induced by nigericin across the planar bilayer lipid membrane (BLM) with the bulk pHs being equal at the opposite sides of the BLM, the formation of the boundary potential difference (delta phi b) on the BLM was observed using the method of the inner membrane field compensation. The increase in the buffer (citrate, phosphate, MES) concentration caused a decrease in the delta phi b. The latter is generated in the presence of phosphatidylserine in membrane-forming solutions only. It was assumed that the steady state difference of the surface hydrogen ion concentration is created under conditions of equal pHs near the BLM surface. In another experimental series the monensin-mediated formation of the surface protein concentration difference gave rise to the formation of a potassium ion gradient induced by nigericin. Thus, a possibility of performing work due to the surface proton concentration gradient was demonstrated. The relevance of these findings to the processes of energy transduction during membrane phosphorylation in mitochondria and chloroplasts is discussed.

[Aperiodic oscillations of the lipid bilayer potential during enzymatic hydrolysis of the permeating substrate]. / Aperiodicheskie kolebaniia potentsiala na bisloinoi lipidnoi membrane pri fermentativnom gidrolize pronikaiushchego substrata.

The experimental system contained a solution with substrate ATEE-ether, a planar bilayer lipid membrane doped with a protonophore and solution with proteolytic enzyme. Oscillations of the electrical potential on the membrane were shown. The magnitude of the potential was proportional to the rate of the reaction under these conditions. This system may prove useful for the study of the peculiarities of enzyme kinetics complicated by the membrane.

[Controlled search for the producers of ionophore antibiotics among Streptomycetes]. / Naprablennyi poisk produtsentov antibiotikov-ionoforov iz streptomitsetov.

A procedure was developed for directed screening of cultures producing ionophore antibiotics among streptomycetes. The procedure is based on measuring the membrane potential generated in the presence of the Men+/nH+ = -expchanger-protonophore couple. It provided isolation of cultures producing ionophore antibiotics at the fermentation broth stage. It was possible to use the procedure in screening both electrogenic and nonelectrogenic ionophores and to rapidly differentiate them. 5 cultures producing ionophore antibiotics were detected with this procedure; 3 of them carry out nonelectrogenic transport of the cations. The cation transport in the other two cultures was electrogenic. Cation selectivity of the antibiotics produced by the cultures was determined with the procedure. An antibiotic identical to indanomycin was isolated from the culture fluid of Streptomyces chromogenes.

[Iodine-containing hormones--dipole modifiers of phospholipid membranes]. / Iodosoderzhashchie gormony--dipol'nye modifikatory fosfolipidnykh membran.

The hormones of thyroid gland thyroxine and triiodothyronine were shown to increase the permeability of bilayer lipid membrane (BLM) and inner mitochondrial membrane for hydrophobic positively charged complex K+-nonactine and to decrease the permeability of these membranes for hydrophobic anion FCCP-. These facts imply that the thyroid hormones affect the phospholipid membranes like the dipole modifyers decreasing the positive potential of hydrophobic region of the membranes in respect to the water phase.

[Transmembrane redox reactions, coupled with proton transfer in lipid bilayer membranes]. / Issledovanie transmembrannykh okislitel'no-vosstanovitel'nykh reaktsii, sviazannykh s perenosom protona na bisloinykh lipidnykh membranakh.

The transmembrane reaction of ferricyanide reduction by exogenous ascorbate in the liposomes in the presence of N,N,N',N'-tetramethylparaphenylenediamine (TMPD) or 2,3,5,6-tetramethylphenylenediamine (DAD) was investigated. The reaction equilibrium was shown to depend on the intraliposomal pH. At alkaline pH values under the experimental conditions used TMPD functions mainly as an electron carrier, while at acidic pH values TMPD effectuates a coupled transmembrane electron and proton transfer. This reaction is paralleled with local changes in the pH values in the unstirred layer near the membrane.

[A model of non-electrogenic cation transport through bilayer lipid membranes]. / Model' neélektrogennogo transporta kationov cherez bisloinye lipidnye membrany.

Quantitative relationship between the proton diffusion potential in the unstirred layers near BLM and NH4Cl was investigated. It has been found that in the range of low concentrations of NH4Cl the potential value depends on the difference of salt concentrations on different sides of the membrane. At higher concentrations the potential value is the function of the ratio of salt concentrations at different BLM sides. In the limiting case the potential value equals 58 mV with NH4Cl concentrations ratio equaling ten. A model is suggested which quantitatively describes the experimental data. It has been shown that the results obtained can be used in determining BLM permeability for weak acids and bases.

[Measurements of non-electrogenic fluxes through lipid bilayers induced by Men+/nH+-exchangers]. / Izmereniia neélektrogennykh potokov cherez bisloinye lipidnye membrany, indutsiruemye Men+/nH+-obmennikami.

In the presence of concentration gradient of metal ions on bilayer lipid membrane (BLM) the addition of non-electrogenic carriers results in a formation of concentration gradient of hydrogen ions in the unstirred layers near membrane. Addition of protonophore under these conditions brings about the formation of diffusion potential of hydrogen ions. This effect underlies the method of measuring non-electrogenic fluxes on BLM initiated in the presence of Men+/nH+ - exchangers. The proposed method was tested on the following Men+/nH+ - exchangers: nigericin, monensin and A23187. The order of cationic selectivity of the given carriers obtained by measuring the potentials on BLM in the presence of protonophores agrees with literature data, which were obtained by direct measurements of ionic fluxes.

[Generation of potential on bilayer lipid membrane in proton combination-separation reactions in the layers adjacent to the membranes]. / Generatsiia potentsiala na bisloinoi lipidnoi membrane pri reaktsii prisoedineniia--otshchepleniia protona v primembrannykh sloiakh.

Addition of uncoupler at the background of concentration gradient of the salts of weak acids and bases (sodium acetate and ammonium chloride) brought about formation of the positive potential on the BLM part with high sodium acetate concentration and of the negative potential on the BLM part with high ammonium chloride concentration. It was shown that the potential formation was conditioned by the initiation of pH gradient in unstirred layers. The effects observed are described by means of the earlier developed [7] model of the transfer of weak acids and bases through BLM. The results obtained show that with the existence of gradients of weak acids and bases potentials may appear on the membrane, biological ones included, in the presence of protonophor.