The influence of cytotoxins from Central Asian cobra venom and melittin from bee venom on the thermodynamic properties of phospholipid bilayer

The interaction of cytotoxin Vc1 and Vc5 from Central Asian cobra and melittin from the bee venom with multilayer liposomes prepared from dimiristoylphosphatidylcholine with an addition of phosphatidic acid have been studied by the method of differential scanning calorimetry. Incorporation of Vc1, Vc5 and melittin into the lipid resulted in pronounced changes in the thermodynamic properties of the lipid. Polypeptides studied induced lateral phase separation in the lipid. Interaction between molecules of the toxins and the lipid resulted in the formation of a new lipid phase characterized by a higher melting temperature and lower phase transition enthalpy.     

Cooperative binding of primycin and gramicidin on erythrocyte membranes. A cation transport study

In this paper the authors present a comparative study of the actions of the antibiotics primycin and gramicidin on the erythrocyte membrane permeability. It has been found that both antibiotics have a nonlinear effect on the membrane permeability. Above a threshold antibiotic concentration, which is characteristic of the type of the antibiotic, the cation permeability of the erythrocyte membranes increases sharply. In the range of nonlinearity the transport-kinetic curves level off before achieving the equilibrium radioactive ion distribution between the extra- and intracellular spaces. A stochastic model of the cooperative and aspecific incorporation of antibiotic molecules into the membrane explains the experimental findings. The authors conclude that membrane permeability increases at the places where two or more antibiotic molecules form aggregates in the membrane.     

TGF-beta 1-induced inhibition of mouse mammary ductal growth: developmental specificity and characterization

TGF-beta 1, implanted into growing mouse mammary glands, was previously shown to inhibit ductal growth in an apparently normal and fully reversible manner. In this report we extend these findings to show that TGF-beta 1 inhibition is highly specific. In pregnant or hormone-treated mice, doses of TGF-beta 1 that were capable of fully inhibiting ductal elongation had little effect on the proliferation of lobuloalveolar structures. Additionally, the inhibitory action of TGF-beta 1 on ducts is epithelium-specific, resulting in cessation of DNA synthesis in the rapidly proliferating epithelium of mammary end buds, but does not inhibit DNA synthesis in the stroma surrounding the end buds. At the cellular level, transplant studies showed that TGF-beta 1 inhibited the regeneration of mammary ductal cells when implanted into mammary gland-free fat pads by suppressing the formation of new end buds, without inhibiting maintenance DNA synthesis in ductal lumenal epithelium; this observation indicates the potential of TGF-beta 1 to maintain patterning by suppressing adventitious lateral branching. The time-course of TGF-beta 1 inhibition of end buds was rapid, with cessation of DNA synthesis by 12 hr, followed by loss of the stem cell (cap cell) layer. The question of glandular exposure to TGF-beta 1 administered in EVAc implants was also investigated. Incorporation of TGF-beta 1 into EVAc was found not to degrade the hormone, while the release kinetics of the ligand from implants, its retention in the gland, and the demonstrable zone of exposure were consistent with observed inhibitory effects. These results support the hypothesis that TGF-beta 1 is a natural regulator of mammary ductal growth.     

Cholesterol-dependent gramicidin A channel inactivation in red blood cell membranes and lipid bilayer membranes

The exchange diffusions of tracer cations (22Na+, 86Rb+) are studied on gramicidin-A-treated red blood cell (RBC) membranes. A time-dependent decrease in cation permeability has been observed and has been considered to be the result of a channel inactivation process. The channel inactivation appears at 20 and 30 degrees C but not at a temperature as low as 6 degrees C. The gramicidin A channel inactivation can be monitored by a conductivity decay of molecular lipid membranes (BLM) prepared either from cholesterol or from a mixture of cholesterol and phospholipids but not of pure phosphatidylethanolamine. The role of cholesterol in the channel inactivation is discussed.     

Quantitative determination of Coomassie R bound to proteins in polyacrylamide gel. A facilitated method for multi-spot analysis of electrograms

Dimethylsulfoxide (DMSO) was found to be an efficient solvent for extraction of Coomassie Blue R 250 (Coomassie R) from stained proteins on polyacrylamide gels. Kinetic measurements show that the extraction of the dye from a 2-D gel reached equilibrium in 48 h. Staining of E. coli ribosomal proteins by Coomassie R dissolved in trichloroacetic acid exhibited two types of dye-protein complexes, the majority of them yield a blue-purple colour, while the rest are stained with a light-blue tone and fluorescent appearance as well. The absorbance spectra of the complexes in the gel matrix differ significantly from each other. However, the DMSO-extracted Coomassie show identical absorbance profiles with lambda max at 602 nm, thus the amount of the bound dye can easily be measured spectrophotometrically.     

On the Theory of Speciation Induced by Transposable Elements

A simple methematical model describes the invasion of panmictic, sexually reproducing populations by a newly introduced transposon. The model places important constraints on the properties that transposons must have to successfully invade a population and describes the kinetics with which such an invasion will occur. Invasibility conditions serve as a basis for new, detailed scenarios whereby transposon-mediated depression in fitness produces reproductive isolation of populations. These scenarios, in turn, lead to several speculations concerning the role of transposons in evolution.     

Mobilization of the transposable element mdg4 by hybrid dysgenesis generates a family of unstable cut mutations in Drosophila melanogaster

Summary A family of unstable mutations at the cut locus in Drosophila melanogaster was obtained under the conditions of hybrid dysgenesis (Gerasimova 1981, 1982). The in situ hybridization experiments have shown that, in the original unstable ct ^MR2 mutation, the 7B region of the X chromosome (where cut is located) contains a mobile dispersed genetic element, mdg4. All other unstable ct mutations derived from ct ^MR2 including visible and lethal alleles and unstable ct ⁺ reversions, also contain mdg4 in the 7B region. The X chromosomes of the parent strain (wild type) do not contain mdg4 at all. All stable revertants derived from ct ^MR2, from other unstable ct mutations, or from ct lethals lost mdg4 from the 7B region. The ct ^MR2 X chromosome does not contain P-elements, although a few copies are present in the autosomes. The instability of the ct ^MR2./ct ^MR2 strain remained at a high level for 50 generations (1.5 years) and then rapidly decreased. A new cross with an MRh12/Cy strain (originally used for dysgenesis induction and containing a number of P-elements) increased the instability to a level exceeding the original one. The data strongly suggest that unstable ct mutations in our system are induced by transpositions of mdg4, possibly activated by P-elements.