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At least 127 records · Page 7Linked to original sources
PubMed2000

Amylin compared with calcitonin: competitive binding studies in rat brain and antinociceptive activity.

Binding studies for rat amylin (AMY) and salmon calcitonin (sCT) were performed on rat membranes prepared from pons and medulla oblongata of rats. The aim was to see whether specific binding sites for AMY and/or for sCT present in these areas could be relevant to some of the biological activities of the two peptides. Binding sites specific for [125I]AMY are present in the pons-medulla of rat brain as AMY, but not sCT, was able to displace radiolabeled AMY binding with an IC50 = 3.7+/-0.5x10(-10) M. In contrast, binding of [125I]sCT was displaced by both sCT and AMY, although with different potencies, the IC50 for sCT being 1+/-0.1x10(-11) M, and for AMY, 1.8+/-0.08x10(-7) M. The functional significance of the presence of these binding sites was evaluated in two different nociceptive tests, hot-plate and tail-flick. In the tail-flick test neither AMY (5-10 microg/rat, i.c.v.) nor sCT (10 microg/rat i.c.v.) showed antinociceptive activity, whereas in the hot-plate test AMY (10 microg/rat, i.c.v.) significantly increased the response latencies as did sCT (250 ng/rat, i.c.v.). These results demonstrated that a 40-fold greater dose of AMY is necessary to produce a comparable antinociceptive effect to that exerted by sCT. These findings are in accordance with the low affinity of AMY for sCT binding sites in rat pons-medulla. It is therefore suggested that the central inhibitory activity of AMY on pain perception involves interaction with sCT receptors whereas the selective AMY binding sites subserve other (as yet unknown) functions.

Amyloid↗
PubMed2002

QSAR study on competition binding of rodenticides (PATs) to H(1) receptor in rat and guinea pig brain.

A quantitative structure-activity relationship (QSAR) study on binding activity for a series of rodenticides (PAT analogues) to the [(3)H]-mepyramine-labeled H(1) receptor in rat and guinea pig brain is attempted topologically. From the pool of molecular descriptors we, observed that the most significant descriptor is the molecular redundancy index (MRI). Multiple regression analysis gave excellent results with MRI upon introduction of some dummy parameters (indicator parameters). Predictive ability of the proposed models is discussed using cross-validation parameters.

Aniline Compounds↗
PubMed1999

Competitive binding of acetate and chloride in photosystem II.

The binding of chloride and acetate to photosystem II (PSII) was examined to elucidate the mechanism of acetate inhibition. The mode of inhibition was studied, and individual binding sites were assigned by steady-state O2 evolution measurements in correlation with electron paramagnetic resonance (EPR) results. Two binding sites were found for acetate, one chloride-sensitive on the electron donor side and one chloride-insensitive on the electron acceptor side. The respective binding constants were as follows: KCl = 0.5 +/- 0.2 mM (chloride binding to the donor side), KI = 16 +/- 5 mM (acetate binding to the donor side), and KI' = 130 +/- 40 mM (acetate binding to the acceptor side). When acetate was bound to the acceptor side of PSII, 200 K illumination induced a narrowed form of the QA-FeII EPR signal, the yield of which was independent of the chloride concentration. When acetate was bound to the donor side, room-temperature illumination produced the S2YZ* state. EPR measurements showed that both the yield and formation rate of this state increased with acetate concentration. Increasing chloride concentrations slowed the rate of formation of the S2YZ* state, but did not affect the steady-state yield of the S2YZ* state. These findings indicate that the light-induced reactions in acetate-inhibited PSII are modulated by both donor side and acceptor side binding of acetate, while the steady-state yield of the S2YZ* state at the high PSII concentrations used for EPR measurements depends primarily on acceptor side turnover. Our data further support a close proximity of chloride to YZ*, indicating a possible role for chloride in the electron-transfer mechanism at the O2-evolving complex.

Acetates↗
PubMed2004

Tuning porphyrin/DNA supramolecular assemblies by competitive binding.

Addition of an intercalating but nonaggregating porphyrin, AuT4, to a preformed adduct between DNA and a strongly aggregating porphyrin, t-H2Pagg, permits control of the extent of aggregation of the latter. The size and the intensity of the ICD and RLS signals depend linearly on the concentration of the intercalating dye and decrease markedly on increasing the concentration of the available binding sites on the biopolymer template.

Binding, Competitive↗
PubMed2001

Competitive binding of aroma compounds by beta-cyclodextrin.

Retention of six aroma compounds has been studied after dehydration of ternary mixtures of aroma water and beta-cyclodextrin. A maximal retention of a mole of aroma per mole of beta-cyclodextrin has been observed for five of the aroma compounds, whereas retention of benzyl alcohol can be twice as high. Retention of a mixture of aroma compounds has also been studied. It has been noted that when volatile compounds compete for the same binding sites on beta-cyclodextrin, ethyl hexanoate, 2-methylbutyric acid, and benzyl alcohol are, respectively, better retained than ethyl propionate, hexanoic acid, and hexanol. Preferential retention observed with esters can be simply explained by their difference of physicochemical properties, but for the acids and alcohols a study at the molecular scale has been necessary. The better retention of 2-methylbutyric acid can be explained by differences in the nature of interaction between the acids and their carrier. At least selectivity of retention noted for the alcohol could be due to a difference in the location of the guest and also a difference in the number of aroma molecules that can be bound per polysaccharide molecule.

Alcohols↗
PubMed2005

Molecular modeling of wild-type and D816V c-Kit inhibition based on ATP-competitive binding of ellipticine derivatives to tyrosine kinases.

The D816V activating mutation of the c-Kit kinase domain often causes human mastocytosis. Although inhibitors of wild-type c-Kit are known (e.g. STI-571), they are at least 10 times less active against the c-Kit mutant. Several derivatives of ellipticine (5,11-dimethyl-6H-pyrido[3,4-b]carbazole), substituted at positions 1, 2, 9, and 11, were found to inhibit purified D816V and wild-type c-Kit kinase domains with comparable potencies by competing with ATP binding. We investigated the difference between these inhibitors by modeling the D816V mutation in crystal structures of inactive and active c-Kit. Molecular dynamics simulations strongly suggested that the D816V point mutation shifts the conformational equilibrium of c-Kit kinase domain toward the active conformation. All ellipticine compounds were subsequently docked to the D816V mutant c-Kit model. The model provides possible explanations for the structure-activity relationships observed among ellipticine compounds, resulting in new insights into D816V c-Kit mutant inhibition.

Adenosine Triphosphate↗
PubMed1997

Competitive binding of alpha-actinin and calmodulin to the NMDA receptor.

The mechanisms by which neurotransmitter receptors are immobilized at postsynaptic sites in neurons are largely unknown. The activity of NMDA (N-methyl-D-aspartate) receptors is mechanosensitive and dependent on the integrity of actin, suggesting a functionally important interaction between NMDA receptors and the postsynaptic cytoskeleton. alpha-Actinin-2, a member of the spectrin/dystrophin family of actin-binding proteins, is identified here as a brain postsynaptic density protein that colocalizes in dendritic spines with NMDA receptors and the putative NMDA receptor-clustering molecule PSD-95. alpha-Actinin-2 binds by its central rod domain to the cytoplasmic tail of both NR1 and NR2B subunits of the NMDA receptor, and can be immunoprecipitated with NMDA receptors and PSD-95 from rat brain. Intriguingly, NR1-alpha-actinin binding is directly antagonized by Ca2+/calmodulin. Thus alpha-actinin may play a role in both the localization of NMDA receptors and their modulation by Ca2+.

Actins↗
PubMed2004

Statistical mechanical approach to competitive binding of metal ions to multi-center receptors.

A microscopic site binding model to treat binding of several metal ions to multi-center receptors is proposed. The model introduces the appropriate parameterization in terms of microscopic complexation constants and metal-metal pair interaction energies. The model is solved with statistical mechanical techniques, including direct enumeration or transfer matrices. We obtain microscopic and macroscopic complexation constants, microstate probabilities, and binding isotherms for chain-like receptors, including the long-chain limit. Various examples to illustrate the usefulness of the model are given.

Binding Sites↗
PubMed1978

Measurement of adenosine 3':5'-cyclic monophosphate by competitive binding to salt-dissociated protein kinase.

An assay for cyclic AMP is described which takes advantage of the high affinity of the dissociated receptor moiety of cyclic AMP-dependent protein kinase I for the nucleotide. The kinase is kept dissociated by salt (800 mM-NaCl/30mM-EDTA). In the presence of a simply prepared heat-stable protein fraction the binding reagent is stable for the time needed to reach equilibrium of binding. A simple procedure [precipitation with poly-(ethylene glycol) followed by DEAE-cellulose chromatography] is described for the separation of protein kinase I from other binding proteins for cyclic AMP in rabbit skeletal muscle. The sensitivity, precision, reproducibility and specificity of the assay compared favourably with those of other cyclic AMP assays. The main advantage of the present assay is its resistance towards non-specific interference from a number of salts, tissue-culture media and substances found in crude tissue extracts. The reliability of cyclic AMP measurement directly in crude tissue extracts was ensured by removal of the assayable cyclic AMP with cyclic nucleotide phosphodiesterase digestion or adsorption with antibody against cyclic AMP, by comparison with measurement in tissue extracts purified by chromatography on QAE-Sephadex or sequentially on Dowex 50, and aluminium oxide as well as by dilution and recovery experiments.

Binding, Competitive↗
PubMed1994

Competitive binding of low molecular mass heparin-tyramine fluorescein-5-isothiocyanate and unlabeled glycosaminoglycans to leukocytes.

Antithrombotic, antiarteriosclerotic, and anti-inflammatory actions of heparins may be mediated by binding of heparin to leukocytes. To get the first information on this hypothesis, fluorescein-labeled LMMH-tyramine has been used (LMMH-tyramine-FITC) to analyze the binding of GAGs to lymphocytes, monocytes, or granulocytes. The fluorescence intensity on leukocytes was quantified by flow cytometry analysis. LMMH-tyramine-FITC bound dose dependently to lymphocytes, monocytes, and granulocytes. PE-labeled CD 11c antibodies identified the specificity of the binding of LMMH-tyramine-FITC to granulocytes. UFH and LMMH displaced LMMH-tyramine-FITC dose dependently from leukocytes. Equimolar ratios of LMMH and LMMH-tyramine-FITC revealed a 50% displacement of the labeled compound, indicating the specific binding by the polysaccharide chain. The synthetic pentasaccharide was 10-fold and dermatan sulfate 100-fold less effective than UFH in displacing LMMH-tyramine-FITC from leukocytes. The data indicate that negatively charged GAGs bind to the surface of lymphocytes, monocytes, and granulocytes. By decreasing the number of negatively charged groups of GAGs, the binding to the surface of leukocytes is decreased. The data obtained with the synthetic pentasaccharide indicate a binding of GAGs to the surface of leukocytes, independently of AT III. The cellular binding of heparins may significantly contribute to its antithrombotic and other biologic activities.

Antigen-Antibody Reactions↗
PubMed1995

Interaction of d-tubocurarine analogs with the Torpedo nicotinic acetylcholine receptor. Methylation and stereoisomerization affect site-selective competitive binding and binding to the noncompetitive site.

Analogs of d-tubocurarine were used to determine the individual effects of methylation, stereoisomerization, and halogenation of d-tubocurarine on the affinity for each of the two acetylcholine (ACh) binding sites of the Torpedo nicotinic acetylcholine receptor (AChR) and for the noncompetitive antagonist site. Eight analogs were synthesized, including three new compounds: 7'-O-methyl-chondocurarine, 12'-O-methyl-chondocurarine, and 13'-bromo-d-tubocurarine. The two ACh sites differ in their affinities for d-tubocurarine by 400-fold, as shown by inhibition of [3H]ACh binding, whereas the affinity ratio for metocurine, the trimethylated derivative of d-tubocurarine, is reduced to 30 due to a decreased affinity for the high affinity site. Binding analysis of five d-tubocurarine analogs demonstrates that methylation of the phenols alone is responsible for the observed changes in affinity. Substitution with bromine or iodine at the 13'-position affected affinity at both sites with a net increase in site selectivity. Stereoisomers of d-tubocurare had decreased affinity for only the high affinity ACh site. Thus, the ring systems, including the 12'- and 13'-positions and the 1-position stereocenter, appear to be important in discriminating between the two ACh binding sites. Desensitization of the AChR was measured by increased affinity for [3H]phencyclidine. Binding to only the single, high affinity acetylcholine binding site, comprised by the alpha gamma-subunits, was required for partial desensitization of the AChR by d-tubocurarine and its analogs. Stronger desensitization, to the same extent observed in the presence of the agonist carbamylcholine, occurred upon binding by iodonated or brominated d-tubocurarine. Interaction of the analogs at the noncompetitive antagonist site of the AChR was also measured by [3H]phencyclidine binding. The bis-tertiary ammonium analogs of either the d- or l-stereoisomers bound to the noncompetitive antagonist binding site of the AChR with 100-fold higher affinity than the corresponding quaternary ammonium analogs.

Animals↗
PubMed1992

Localized conformational changes in the N-terminal domain of CD4 identified in competitive binding assay of monoclonal antibodies and HIV-1 envelope glycoprotein.

The CD4 antigen is established as a major cellular receptor for the human immunodeficiency virus (HIV). Previous studies have suggested that certain anti-CD4 monoclonal antibodies (MAbs) can inhibit or enhance the binding of the viral envelope glycoprotein gp120 to CD4 by allosteric effects. In the study reported here, 17 anti-CD4 MAbs were tested for their ability to influence the binding of each other to recombinant soluble CD4 in a solid-phase radioimmunoassay. Marked enhancement of binding between specific pairs of MAbs was seen, as well as inhibition or lack of interaction. Enhancement was seen less often when CD4+ cells were used as the target antigen. Information on patterns of enhancement and inhibition permitted grouping of MAbs on the basis of epitope specificity, and this grouping was in agreement with published findings based on X-ray crystallographic studies. These results demonstrate connectivity between epitopes in the first domain of recombinant CD4 and suggest a high degree of flexibility of surface structure. These findings may be of physiological significance both in the normal function of CD4 and in the interaction of CD4 with HIV. The data have implications for research or therapeutic strategies based on recombinant CD4 or CD4 mutants and highlight the problems of interpreting experimental findings based on abrogation of MAb binding.

Antibodies, Monoclonal↗