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At least 865 records · Page 48Linked to original sources
PubMed1996

Macromolecule-macromolecule interaction in drug distribution. IV. Molecular weight dependency in the interaction of fractionated [3H]heparin with plasma proteins.

Molecular weight dependency in the interaction of fractionated [3H]heparin (FH) with plasma proteins was evaluated by determining the protein binding of low molecular weight fractionated [3H]heparin (LMWFH: 7000 Da) and high molecular weight fractionated [3H]heparin (HMWFH: 16000 Da) by ultrafiltration and the effects of plasma proteins on the uptake in rat hepatocytes in primary culture. The unbound fractions of LMWFH were 0.5 and 0.8 in the presence of alpha-globulin and albumin, respectively, and were about 10 times larger than those of HMWFH, 0.04 and 0.1, suggesting a reduction in binding with a decrease in molecular weight. However, while the uptake of LMWFH was reduced by these proteins by the extents similar to bound fractions of LMWFH, the uptake of HMWFH was reduced by extents far smaller than bound fractions and comparable with those for LMWFH. Thus, it seemed that, while only unbound LMWFH is available for uptake, HMWFH bound to proteins is to some extent available for uptake (protein-mediated transport). The protein-mediated transport of heparin seemed to reduce with a decrease in molecular weight. It was also shown that the extended uptake of LMWFH was smaller than that of HMWFH not only in the absence of proteins but also in the presence of alpha-globulin, the major binding protein. The lower uptake of LMWFH is consistent with in vivo suggestion of lower hepatic accumulation.

Animals↗
PubMed1976

Interaction of radionuclides with organic matter dissolved in seawater. Interaction of radiocobalt with some amino acids.

The interaction of radiocobalt with glycine, alanine or aspartic acid dissolved in seawater was investigated by means of adsorption on Chelex 100, solvent extraction with dithizone or gel filtration chromatography. Although the distribution coefficients of Co on Chelex 100 decreased gradually with ageing even in the absence of organic matter, much more decreases were observed in the presence of the amino acids. The distribution coefficients on the resin reached equilibrium states in about 20 days. The extraction of cobalt with dithizone in carbon tetrachloride was also inhibited in the presence of the amino acids. Alanine and aspartic acid showed a similar interfering tendency in both adsorption on Chelex 100 and dithizone extraction, while glycine inhibited dithizone extraction more than adsorption on Chelex 100. From the fractionation of Co by Sephadex G-10 gel filtration chromatography, the higher molecular species of Co associated with the amino acids occurred after several days ageing and then increased together with decreasing in the lower molecular species.

Adsorption↗
PubMed1999

Probability description of ligand-receptor interactions. Evaluation of reliability of events with small and supersmall doses. I. Kinetics of ligand-receptor interactions.

We have developed mathematical methods for describing ligand-receptor interactions (LRI) using Markov chains. Under some conditions, the mean value of ligand-receptor complexes obtained using Markov chains coincides with that obtained from the law of mass action. Using the calculated ratio of standard deviation to mean number of ligand-receptor complexes, we show that with small concentrations of ligand-receptor complexes LRI must be described using probability methods. Using data from the literature, we show that LRI description using the mass-action law under these conditions can cause significant errors in interpretation of experimental data.

Binding Sites↗
PubMed1992

Disintegrins: RGD-containing proteins which inhibit cell/matrix interactions (adhesion) and cell/cell interactions (aggregation) via the integrin receptors.

Whereas many attempts have been made to generate synthetic, high affinity, linear RGD-peptides (Arginine-Glycine-Aspartic acid), by analogy with glycoprotein ligands to integrins, success has been limited. What has emerged is that the stereochemistry of the Arg-Gly-Asp-X (RGDX) recognition sequence is essential to ligand binding. This has led to the study of small, chemically synthesised, cyclic-RGD peptides. Another approach is to study the disintegrins. These high-affinity RGD-polypeptides (50-90 KDa) from viper venoms are "natural" ligands to integrins, presumably as inhibitors of physiological ligands such as fibrinogen. A study of the disintegrins may shed some light on the preferred conformation of the active form of RGD, as well as the contribution of other potential recognition motifs in these molecules to modulate RGD interactions with receptors (fig. 1).

Cell Adhesion↗
PubMedDate not supplied

[The intercellular interactions in the interphase death of irradiated thymocytes. A study of the nature of the mediator of the interaction of irradiated thymocytes].

A study was made of the influence of cytosol and conditioned medium, obtained at different times of incubation of irradiated thymocytes, on native thymocytes, as well as of the influence of mixing the suspension and changing the medium and the enzyme inhibitors, involved in metabolism of arachidonic acid, on the radiation injury to thymocytes. Cytosol of thymocytes, incubated for 60 min after irradiation, was shown to exert an insignificant toxic effect on native thymocytes. The conditioned medium of irradiated thymocytes is virtually ineffective. The mixing of the suspension upon incubation and the changing of the medium reduced the damage to exposed thymocytes while inhibitors of phospholipase A2 and lipoxygenase prevented completely the radiation-induced pyknosis of nuclei, whereas a inhibitor of cyclooxygenase did not influence it. It is inferred from the data obtained that unstable lipoxygenase products may serve as mediators of intercellular interactions of exposed thymocytes.

Acetophenones↗
PubMed1975

Steroid-protein interactions. Stopped flow fluorescence studies of the interaction between steroid hormones and progesterone-binding globulin.

Stopped flow fluorometry, measuring changes in the intrinsic fluorescence of progesterone-binding globulin (PBG), was used to determine the association and dissociation rates of the interaction of PBG with seven delta4-3-ketosteroids. The rates of formation and dissociation of the PBG-progesterone complex were measured as a function of concentration and temperature. At 20 degrees, kon = 8.7 X 10(7) M-1 S-1 and koff = 0.060 S-1. The association rate constants for progesterone, deoxycorticosterone, testosterone, testosterone acetate, and medrogestone were found to be the same within experimental error. The different affinities of PBG for these steroids result from the dissociation rate constants of the steroids which ranged from 0.43 S-1 for testosterone to 0.024 S-1 for medrogestone. Two corticosteroids, corticosterone and cortisol, were both bound somewhat more slowly (approximately 5 X 10(7) M-1 S-1). Reflecting their very low affinity for PBG both steroids dissociate very rapidly: corticosterone at 1.4 S-1 and cortisol at 90 S-1. The ratio of association to dissociation rate constants gave affinity constants in agreement with independently determined constants.

Animals↗
PubMed1990

Mechanism of MHC class II restriction in the interaction between specific suppressor and responder T cells in a proliferative response: Ia interaction with a putative anti-self receptor, expressed on pre-activated responder cells.

For the inhibition of T-lymphocyte proliferation in mixed lymphocyte culture (MLC) by in vivo alloantigen-induced specific T-suppressor cells (Ts), the Ts and responder cells must have major histocompatibility complex (MHC) class II identity, either in I-C or in I-A + I-E. In the case of I-C, the molecule is on the surface of the Ts and not on the surface of the stimulator or responder cells. This lack of I-C on the responder cells occurs even after pre-activation by antigen. I-J on the Ts is unimportant in the present system. By blocking the Ts surface molecules with antibody, it was shown that the two Ts genetic restrictions were due to distinct Ts subsets, bearing I-C in one case and I-A + I-E in the other. Pretreatment of the Ts with anti-I-C antibodies (without complement) did not prevent specific Ts binding to the alloantigen, as shown by absorption on monolayers. However, it blocked the ability of the Ts to cause suppression and this could be reversed by removal of the antibody with pronase. The responder population, when pre-activated, could be fractionated by absorbing on monolayers of syngeneic Ts. Under these conditions, the cells sensitive to suppression adhered to the monolayer, while the non-adherent cell could not be suppressed. It is proposed that a receptor, to an Ia molecule (I-C or I-A + I-E) of the Ts, appears on the surface of the pre-activated responder T cell and that this is required for the genetically restricted interaction between the responder cell and the Ts.

Animals↗
PubMed1978

Interaction of metal ions with nucleic acids. Interaction of copper(II) with guanosine and its derivatives.

Interaction of copper(II) with guanosine, 2'-deoxyguanosine, 1-methylguanosine, 7-methylguanosine and GMP was studied withe use of spectroscopic and magneto-chemical methods. The main site of copper(II) binding in guanosine is nitrogen N-7; participation of N-1 is not excluded. The involvement of carbonyl oxygen in copper binding or copper chelation to N-7 and 0-6 is rather unlikely. A crystalline complex of copper(II) with GMP [Cu(C10H12O8N5P) .(H2O)3] was obtained, and it was demonstrated that copper(II) is bound with N-7 and the phosphate group.

Binding Sites↗
PubMed1987

Glycoprotein-concanavalin A interaction: role of protein conformation in the specific interaction of glycoprotein with concanavalin A.

The specific binding of two glycoproteins, ovomucoid and ovalbumin to concanavalin A was studied in 0.01 M Tris-HCl buffer, pH 7.4, containing 0.2 M NaCl and 1 mM each of magnesium acetate, calcium acetate and manganese chloride at 30 degrees C. Native ovalbumin was a better ligand than ovomucoid in its reaction with concanavalin A-sepharose 4B; in the inhibition of the lectin binding to dextran and cross-linked dextran, Sephadex G-150, and in the rate of precipitin reaction. Reduction of disulphide bonds of the two glycoproteins with 2-mercaptoethanol and subsequent alkylation with iodoacetate produced significant conformational change as evidenced by the increase in the hydrodynamic volume measured by intrinsic viscosity. The native and modified glycoproteins were indistinguishable in inhibiting the binding of dextran and Sephadex G-150 to the lectin, however, their pronase digest (or glycopeptides) were most effective inhibitors. Substantial (4-fold) decrease in the rate of precipitin reaction of the lectin with glycoprotein which was noted with conformationally altered glycoproteins suggested the importance of native protein conformation in the specific interaction of the two glycoproteins with concanavalin A.

Alkylation↗
PubMed1986

Modelling the interaction of small organic molecules with biomacromolecules. II. A generalized concept for biological interactions.

In the first part of this series it was shown that, for interactions between substituted pyridines and anti-3-azopyridine antibody, the maximum biological activity is observed for an optimum electronic correspondence between the reactants. This particular result, together with data in the literature which points to the necessity for geometrical and lipophilic correspondence, supports a generalization for the nature of the biological action of chemical compounds. Accordingly in this paper it is proposed that the affinity towards a given biomacromolecule will be maximum only for those chemicals within a series of compounds which are characterized by optimum values of basic factors which condition the biological activity: geometric, electronic, and/or lipophilic. The practical aspects of the hypothesis should be valuable in molecular pharmacology, drug design, and theory of chemical reactivity.

Aminopyridines↗
PubMed1986

[Interactions between herbicides and various of the most frequently used drug groups. I. Interactions between chronically administered herbicides: carbendazyme, 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid and drugs affecting the circulatory system].

The influence of chronically administered (6 weeks) herbicides (KAR, 2,4-D and 2,4,5-T) on pharmacological effects of quinidine, reserpine and strophantin K in mice and rats was examined in vivo. The investigated herbicides produced in mice an increase in acute toxicity of strophantin K, the acute toxicity of either reserpine oro quinidine being unchanged. The herbicides alone, after 6 weeks administration, significantly increased mean arterial pressure of rats, however the hypotensive response to reserpine was not statistically influenced in these animals as compared with controls. The prolonged administration of investigated herbicides produced also the increased sensibility of heart to the arrhythmic effects of quinidine and ouabain as observed in the ecg pattern in rats treated with increasing doses of these agents. The studies indicate the significance of the possible pharmacological interactions between the drugs affecting cardiovascular system and commonly used herbicides in men.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMedDate not supplied

[Fiber interaction during impulse propagation in smooth muscle and myocardial tissues. Electrotonic interaction].

Electrotonic potential appearing in a single muscle fibre during excitation spread was calculated in the mathematical model of closely packed parallel fibres. Electrotonic depolarization values for heart and smooth muscle were shown to be 10--20 mV, that is comparable to the excitation threshold value. Tissue parameter values were estimated where the coupling coefficient was maximal. The parameter values proved to be similar to those measured in heart and smooth muscles. The data obtained indicate that the electrotonic interaction of muscle fibres should play a significant role in excitation conduction.

Cell Communication↗
PubMedDate not supplied

[Interaction of lambda bacteriophages with mammalian cells. II. Elucidation of the role of interacting components].

The study of 3H-thymidine labelled bacteriophage lambda C185757 uptake by HeLa, RH and Chinese hamster cell revealed the lack of cells or phage specificity in the phage interaction with cells. The phage uptake is shown to be an active process depending on the cell state. The mechanism of "protective" action of calcium chloride is found to be as follows: the calcium phosphate precipitate formed in phosphate-containing media absorbs the phage, thus increasing its concentration on the cell surface, which makes the pinocytosis more effective.

Animals↗
PubMed1984

Bridging the gap: parent-child play interaction and peer interactive competence.

A multimeasure, multicontext study of the relationship between father-child and mother-child play and children's competence with preschool peers was conducted. 13 boys and 14 girls, ages 3-4 years, and their parents participated. Children were videotaped while playing with each parent separately for 20 min in their homes. Children's social competence with their peers was independently evaluated by 3 measures: (1) rankings of preschool teachers of popularity with peers, (2) Q-sort ratings of children's competence by their teachers, and (3) assessments of social interaction with 3 different preschool peers on separate occasions. Differential patterns of maternal and paternal behavior were associated with the social competence of boys and girls. Paternal physical play, engagement, and maternal verbal behavior were positively related to children's peer relations, especially for boys. Paternal directiveness was negatively related to popularity for boys and girls, while maternal directiveness was positively linked with popularity for girls. Opportunities for learning to regulate affect are hypothesized to contribute to these relationships. The study illustrates the linkages between family and peer social systems.

Affect↗
PubMedDate not supplied

[Mechanism of codon-anticodon interaction in ribosomes. Interaction of aminoacyl-tRNA with 70S ribosomes in the absence of elongation factor EF-Tu and GTP].

Purified Phe-tRNAPhe revealed higher affinity to the donor (D) site of vacant 70S . poly(U) complex than to the acceptor (A) site, independent on Mg2+ concentration. As a result, in excess of ribosomes Phe-tRNAPhe binds exclusively to the D site. This was proved using the tests in the presence of tetracycline and puromycin. Preferential binding of Phe-tRNAPhe to the D site was used to measure equilibrium association constants of this interaction at different temperatures and Mg2+ concentrations. A large value of reaction enthalpy (ca. -26 Kcal/mole) was found.

Anticodon↗
PubMed1982

Nicotinic-catecholaminergic interactions in rat brain: evidence for cholinergic nicotinic and muscarinic interactions with hypothalamic epinephrine.

The i.p. injection of nicotine produced several changes in regional catecholamine concentrations in rat brain. These changes were blocked by the centrally active nicotinic antagonist mecamylamine, but not by the quaternary nicotinic antagonist hexamethonium. An examination of the effects of various cholinergic agents on hypothalamic epinephrine concentrations revealed several interesting findings. Central muscarinic antagonism or peripheral muscarinic agonism decreased hypothalamic epinephrine concentrations. The anticholinesterase physostigmine decreased hypothalamic epinephrine concentrations and this effect was blocked by the centrally acting nicotinic antagonist mecamylamine, but not by hexamethonium, scopolamine or methscopolamine. These findings indicate an interaction of cholinergic receptors, both nicotinic and muscarinic, with hypothalamic epinephrine.

Animals↗
PubMed1982

Kinetics of interaction of immune complexes with complement receptors on human blood cells: modification of complexes during interaction with red cells.

Antigen-antibody complexes, composed of 125I-BSA and guinea-pig or rabbit antibody, were incubated at 37 degrees C with human blood cells suspended in autologous serum and kinetics of binding analysed. When purified polymorphonuclear (PMN) or mononuclear cells (MNC) were studied, maximum binding was observed within 8 min, and immune complexes (IC) remained associated with cells even after 1 hr. When cells were studied unseparated (in the same amount of serum), maximum binding was observed slightly earlier (within 4 min), but within 15 min most of the IC were found in the serum. Separation of cell types at the time of maximal binding and studies with cell preparations depleted of different elements revealed that binding was principally to red blood cells (RBC). IC recovered in the serum 16 min after addition to unseparated cells bound very slowly to purified PMN or MNC; binding after 30 min was 10-15% of that observed with fresh IC at 8 min. Ultracentrifugal analysis revealed that reduction in binding efficiency correlated with decrease in the size of IC. RBC isolated after binding and release of IC bound newly-formed IC was identical rapidity and capacity as fresh RBC, indicating that receptors were not altered by IC. Kinetics studies with serum in the absence of cells suggested that interaction with RBC accelerated the rate of change in binding properties of IC. Rates of binding and release were independent of antigen/antibody ratio but were slowed and binding to RBC sustained when diluted or hypocomplementaemic (SLE) serum was substituted for neat serum. Our results suggest that competition for IC by RBC is associated with loss of ability of IC to bind to other blood cell types and reduction in size of IC, and that abnormalities of complement can lead to prolonged association of IC with RBC.

Antigen-Antibody Complex↗