Use of specific angiotensin inhibitors in the study of hormone-receptor interaction]

The specificity of receptors participating in the interaction with angiotensin II (AT 1--8) fragments, e. g. N-terminal tri-(AT 1--3), C-terminal penta-(AT 4--8), and middle tetrapeptide (at 3--6), was studied in experiments on rat ascending colon which were performed to investigate the influence of a specific angiotensin antagonist, /1-hydantoic acid, 5-valine, 8-alanine/-angiotensin (HAAT 1--8), on myotropic effects of these fragments as well as the influence of the fragments on the myotropic activity of the whole hormone molecule. Competitive antagonism was found between HAAT 1--8 and AT 4--8 and AT 3--6 and between these fragments and AT 1--8. No antagonisma was revealed between AT 1--3 and HAAT 1--8, and between AT 1--3 and AT 1--8. It is assumed that the fragments AT 4--8 and AT 3--6 interact at the level of angiotensin receptors, and that of AT 1--3 at the level of non-specific receptors. A new model for the structural and functional organization of angiotensin is proposed.     

Electron microscopic study of the I, II phases and R-forms of Sh. sonnei]

Electron microscopic study of the microbial cells of the I, II phases and the R-form was carried out. Intact cells were examined by negative contrasting, and morphological differences of various bacterial phases were shown: cells of the I phase had a relatively smooth surface, bacteria of the II phase had a smooth surface, but many cell wall fragments were split from them; the surface of the R-form cells was coarse, folded, and cell wall fragments were split from the majority of bacteria. Antigenic determinants responsible for phasic specificity in bacteria of the I and II phases were located at some distance from the external membrane of the cell wall; as to the R-form cells--they were localized on the wall.     

Electron microscopic study of the interaction between cytolytic T-lymphocytes and target cells]

Thymocytes stimulated in vitro in a mixed culture was sorbed by centrifugation on the surface of target cells for electron microscope study of cytology of immune T-lymphocytes and early cytolysis periods. A well developed Golgi apparatus was revealed in the cytoplasm of lymphocytes; there was also accumulation of tubular structures 50 to 60 nm in diameter which communicated with the cysterns of the granular endoplasmic reticulum, with "descended" vesiculi and plasmatic membrane of lymphocyte. This membrane formed numerous contacts with the membrane of target cells thus producing closed clefts. Taking into consideration these data and also current views on the intertransformation of membranes and intracellular transport a hypothetic scheme of the mechanism involved in the cytolysis of the target cell by immune T-lymphocyte was put forward.     

A study of the interaction of boraadamantane with liposomes

Changes in the surface potential of liposomes obtained from dipalmitoyl phospatidylcholine during their interaction with the new antiviral preparation boraadamantane (BG-12) have been studied. It has been concluded that the saturation of the lipid bilayer of liposomes by the BG-12 preparation occurs at its concentrations above 10 μg/mL.     

An ellipsometric study of the antigen-antibody interaction in the interphase solid/solution area]

Ellipsometric studies have proved that monoclonal immunoglobulin G(IgG) against gamma-interferon (gamma-INF) and immunoglobulin fraction (Ig-fraction) of rabbit blood serum against human serum albumin (HSA) are adsorbed according to the Langmuir model on the surfaces of mirror plates of covalently modified gamma-INF or HSA, respectively. The maximum surface concentrations (Tmax) and equilibrium adsorption constants (K) for IgG and Ig-fraction are equal to 2.57 pmol/cm2 and 2 x 10(7) M-1, 3.3 mg/m2 and 0.1 cm3/micrograms, respectively. The additional treatment of gamma-INF modified surfaces with Tween-20 leads to an increase of K IgG ut to 2.7 x 10(-7) M-1 while Tmax decreases up to 1.12 pmol/cm2 which is conditioned by the blocking of protein non-specific binding sites. The role of specific and non-specific interactions of IgG and Ig-fraction with covalently immobilized antigens was studied at antibody-antigen mixture adsorption. The necessity to apply this method to quantitative determination of gamma-IHF and HSA in solutions was proved.     

A thermodynamic study of sperm-egg interaction.

We have studied the binding of spermatozoa to the receptor sites on the vitelline coat (VC) of glycerol-treated eggs (ghost eggs) of the Ascidian, Ciona intestinalis (Protochordate). Glycerol treatment cytolyses the egg without affecting the ability of the VC to bind spermatozoa in a species-specific manner; however, in this system binding is not followed by the acrosome reaction. The ghost eggs are metabolically inert. As a base line for our analysis, we have studied the concentration-dependent heat evolved and oxygen consumption of spermatozoa when diluted in sea water. The process has been analyzed on the basis of equations derived by Liquori and Tripiciano to describe cell growth. Upon binding to the ghost eggs, the spermatozoa produce an explosive heat evolution (excess heat) which is not accompanied by oxygen consumption. The excess heat produced plotted against sperm concentration (at constant egg concentrations) gives an asymmetric bell-shaped curve. This is interpreted as being due to the competitive effect of sperm agglutination at a high sperm concentration. It is concluded that only spermatozoa that attach singly (monomeric spermatozoa) to the egg undergo metabolic activation.     

A fluorometric study of the interaction of bradykinin with lipids

The interaction of bradykinin (BK) with lipids has been followed by steady-state fluorescence measurements. Addition of either cerebroside sulfate (CS) or phosphatidylinositol (PI), solubilized with the nonionic surfactant C12E8, to BK or its analogue [Gly6]-BK enhances the relative fluorescence intensity of peptide emission at 288 nm. Fluorometric titration of the peptide with lipid has been used to quantitate the interactions in terms of stoichiometry and equilibrium constant. Job's method of continuous variation for the BK-CS interaction gave a stoichiometry of 1:2 for the complex. The value of the equilibrium constant, K, for the interaction of either BK or [Gly6]-BK with CS is 1.5.10(4) M-1. The BK-PI interaction is weaker; K = 5.0.10(3) M-1. Although electrostatic forces no doubt play a major role in these interactions, measurements on the model peptide Gly-Phe-Gly indicate that the phenylalanine residues of BK are disposed in the hydrophobic environment provided by the lipid-C12E8 mixed micelle. 13C-NMR measurements on [99% 13C alpha-Gly6]-BK show that there is no change in its cis/trans ratio upon interaction with CS. The increase in the relative fluorescence intensity of BK accompanying its cooperative interaction with sodium dodecyl sulfate (SDS) implicates the role of hydrophobic forces in this interaction as well. These results bear on the interpretation of the changes in circular dichroism (CD) of BK caused by SDS.     

Protein-ligand interaction. A calorimetric study of the interaction of oligosaccharides and hen ovalbumin glycopeptides with concanavalin A

A calorimetric study is reported concerning the interaction between concanavalin A (Con A) and some oligosaccharides and glycopeptides hydrolyzed from hen ovalbumin. The measurements were carried out in acetate buffer, pH 4.5, where, by far, the prevailing form of the protein is the dimeric one [Kalb, A.J., & Lustig, A. (1968) Biochim. Biophys. Acta 168, 366; Dani, M., Manca, F., & Rialdi, G. (1981) Biochim. Biophys. Acta 667, 108]. The calorimetric technique allows the direct determination of the binding enthalpy delta H, degrees B, the evaluation of the apparent association constant K'B, and then the evaluation of the apparent free energy and entropy, delta G degrees' B and delta S degrees' B. Three groups of data have been collected in the present study. The first one concerns the interaction between concanavalin A and some mono- and disaccharides [methyl alpha-glucopyranoside (alpha MGlup), methyl alpha-mannopyranoside (alpha MManp), D-maltose, D-trehalose, and D-cellobiose]. The analysis of the data indicates that in these cases there are small favorable entropic and enthalpic contributions to the affinity. The stoichiometry of the reaction is 2 mol of ligand/mol of Con A dimer, the sites resulting being equivalent and noninteracting. Melezitose, the only trisaccharide studied, shows a different behavior: its affinity for Con A is higher as compared to the other oligosaccharides containing alpha-glucosyl residues and closer to that of methyl alpha-mannopyranoside. However, the stoichiometry is different, namely, 1 mol of ligand/dimer of Con A.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of the fluorescent probe method to study the interaction of barbiturates with biological membranes]

The binding of the negatively charged fluorescence dye ANS and neutral dye NPN2 with lipid and erythrocyte membranes in the presence of barbiturates was studied. It was found that barbiturates decreased the amount of binding sites of ANS and NPN2 with membranes did not affect the quantum yield and the dissociation of the membrane-dye complex. It was shown that all barbiturates investigated were bound with the membranes in a neutral form.     

Phenological phases of the host plant shape plant–treehopper interaction networks

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An electron microscopic study of the interaction of bacterial intestinal microflora and rotavirus virions]

Transmission electron microscopy has revealed the capacity of rotaviruses for adsorption on Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis cells and the absence of such capacity with respect to Enterococcus faecalis, Lactobacillus casei and Edwardsiella tarda. Different degrees and a varying character of the adsorption of rotaviruses by the representatives of the opportunistic group of bacteria have been established, which may aggravate the course of rotavirus diarrhea due to the aggregation of viral particles. For the first time the phenomenon of the selective destructive adsorption of rotaviruses by E. coli indigenous strains M-17 and 33/29, typical representatives of normal enteric microflora, is described. This observation should be regarded as one of important biological mechanisms responsible for the protection of the body from rotavirus infection.