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At least 739 records · Page 41Linked to original sources
PubMed1986

Thermodynamic and kinetic studies on saccharide binding to soya-bean agglutinin.

The fluorescence of N-dansylgalactosamine [N-(5-dimethylaminonaphthalene-1-sulphonyl)galactosamine] was enhanced 11-fold with a 25 nm blue-shift in the emission maximum upon binding to soya-bean agglutinin (SBA). This change was used to determine the association constants and thermodynamic parameters for this interaction. The association constant of 1.51 X 10(6) M-1 at 20 degrees C indicated a very strong binding, which is mainly due to a relatively small entropy value, as revealed by the thermodynamic parameters: delta G = -34.7 kJ X mol-1, delta H = -37.9 kJ X mol-1 and delta S = -10.9 J X mol-1 X K-1. The specific binding of this sugar to SBA shows that the lectin can accommodate a large hydrophobic substituent on the C-2 of galactose. Binding of non-fluorescent ligands, studied by monitoring the fluorescence changes when they are added to a mixture of SBA and N-dansylgalactosamine, indicates that a hydrophobic substituent at the anomeric position increases the affinity of the interaction. The C-6 hydroxy group also stabilizes the binding considerably. Kinetics of binding of N-dansylgalactosamine to SBA studied by stopped-flow spectrofluorimetry are consistent with a single-step mechanism and yielded k+1 = 2.4 X 10(5) M-1 X s-1 and k-1 = 0.2 s-1 at 20 degrees C. The activation parameters indicate an enthalpicly controlled association process.

Acetylgalactosamine↗
PubMed1984

Kinetics of binding to opiate receptors in vivo predicted from in vitro parameters.

In order to determine the relationship between in vitro and in vivo binding of opiates in the CNS, the in vitro and in vivo binding properties of 9 opiates, including agonists and antagonists, were studied in mouse brain. Equilibrium dissociation constants (KD) were measured in the presence and absence of 100 mM NaCl and 100 microM 5-guanylylimidodiphosphate (GMP-PNP) at 37 degrees C in mouse brain homogenates. The rate constants describing the exponential clearance of the specifically-bound (i.e. receptor-bound) fraction of ligand in vivo were measured in the striatum, thalamus and cortex. A mathematical model was formulated which relates the in vivo clearance rate for the specifically-bound fraction to the association and dissociation rate constants, the local density of receptors and a parameter which determines the rate at which ligand can diffuse out of the local receptor compartment. The diffusion parameter takes on two forms depending on whether ligand is transported out of the local receptor compartment by simple diffusion or by permeation of a non-polar membrane barrier. In the case of membrane permeation, the model is dependent on the diffusion constant and the lipophilicity of the ligand. A correlation between the in vitro and in vivo measurements is obtained only when KD is measured in the presence of 100 mM NaCl and 100 microM GMP-PNP and when the lipophilicity of the ligand is incorporated into the model. The model corresponds to the physical situation where continuous rebinding of ligand to receptors takes place in the vicinity of a high local density of receptors (possibly at a synapse), thereby retarding the clearance of the specifically-bound ligand from the brain. The rebinding effect is accentuated by: (1) a high local density of receptors; (2) a small KD (measured in the presence of 100 mM NaCl and 100 microM GMP-PNP); (3) a low lipophilicity; and (4) a high molecular weight.

Animals↗
PubMed1996

[3H]2-(2-benzofuranyl)-2-imidazoline: a new selective high affinity radioligand for the study of rabbit brain imidazoline I2 receptors.

This is the first study characterising the binding of the new imidazoline I2 receptor selective radioligand [3H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) to rabbit brain membranes. [3H]2-BFI binding was found to be saturable and of high affinity identifying two binding sites with KD1 = 0.27 nM, Bmax = 111.2 fmol mg-1 protein and KD2 = 8.97 nM, Bmax = 268 fmol mg-1 protein. Specific binding represented greater than 90% of total binding. Kinetic studies revealed that the binding was rapid and reversible and also showed [3H]2-BFI interacted with these two sites or two affinity states. In competition binding studies against [3H]2-BFI (0.3-InM) idazoxan, 2-BFI, cirazoline, guanabenz, naphazoline, amiloride and BU224 (2-(4,5-dihydroimidaz-2-yl-quinoline) displaced with high affinity. In contrast the alpha 2-adrenoceptor antagonists efaroxan and rauwolscine, the I1 site selective drug moxonidine, the monoamine oxidase-A inhibitor clorgyline and the proposed endogenous imidazoline receptor ligand, agmatine, were weak at displacing [3H]2-BFI binding. These findings are consistent with [3H]2-BFI recognising imidazoline receptors of the I2 subtype in rabbit brain.

Affinity Labels↗
PubMed1986

Effect of amiodarone on Na+-, K+-ATPase and Mg2+-ATPase activities in rat brain synaptosomes.

Amiodarone hydrochloride is a diiodinated antiarrhythmic agent widely used in the treatment of cardiac disorders. With the increasing use of amiodarone, several untoward effects have been recognized and neuropathy following amiodarone therapy has recently been reported. The present studies were carried out to study the effect of amiodarone on rat brain synaptosomal ATPases in an effort to understand its mechanism of action. Na+, K+-ATPase and oligomycin sensitive Mg2+ ATPase activities were inhibited by amiodarone in a concentration dependent manner with IC50 values of 50 microM and 10 microM respectively. [3H]ouabain binding was also decreased in a concentration dependent manner with an IC50 value of 12 microM, and 50 microM amiodarone totally inhibited [3H]ouabain binding. Kinetics of [3H]ouabain binding studies revealed that amiodarone inhibition of [3H]ouabain binding is competitive. K+-activated p-nitrophenyl phosphatase activity showed a maximum inhibition of 32 per cent at 200 microM amiodarone. Synaptosomal ATPase activities did not show any change in rats treated with amiodarone (20 mg kg-1 day-1) for 6 weeks, when compared to controls. The treatment period may be short, since the reported neurological abnormalities in patients were observed during 3-5 years of treatment. The present results suggest that amiodarone induced neuropathy may be due to its interference with sodium dependent phosphorylation of Na+, K+-ATPase reaction, thereby affecting active ion transport phenomenon and oxidative phosphorylation resulting in low turnover of ATP in the nervous system.

4-Nitrophenylphosphatase↗
PubMed1995

Kinetics of nucleotide binding to pyruvate carboxylase.

The kinetics of nucleotide binding to pyruvate carboxylase have been studied by measuring the fluorescence changes that occur on the binding and release of FTP and FDP, which are fluorescent formycin analogues of ATP and ADP. The rate constants and equilibrium binding constants for both MgFTP and MgFDP binding to pyruvate carboxylase have been determined. From the kinetics of displacement of MgFTP by MgATP and binding of MgFTP in the presence of MgATP, the rate constants of MgATP binding were estimated. A slow component to the fluorescence changes was seen to occur after the initial rapid, bimolecular binding step, when formycin nucleotides were mixed with the enzyme. HCO3- and pyruvate were shown to quench the fluorescence of enzyme-bound MgFTP, but did not affect the affinity of the enzyme for the nucleotide. Acetyl CoA reduced the affinity of the enzyme for both MgFDP and MgFTP by about 3-fold by decreasing the association rate constants (by 25%) and increasing the dissociation rate constants (by 2-fold). In the absence of Mg2+ a very rapid component to FTP binding was observed that was complete within about 3 ms, but no fast component was observed comparable to that seen in the presence of 4.5 mM MgCl2. Increasing the [Mg2+] gradually abolished this very fast component of the binding, while the amplitude of the fast component increased, although the rate constant for this component did not appear to be strongly dependent on [Mg2+]. The rate constants of the slow component of Mg.formycin nucleotide binding did not appear to be dependent on nucleotide concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyl Coenzyme A↗
PubMedDate not supplied

Application of competition kinetics to investigate rat brain muscarinic receptors.

We have recently developed a method for obtaining kinetic parameters of unlabeled ligands that is based on analyzing the effect of their competition on the binding kinetics of a labeled ligand. We employed this method to investigate the kinetics of muscarinic agonist binding to rat brain medulla-pons homogenates. The agonists studied were acetylcholine, carbamylcholine and oxotremorine, with N-methyl-4-[3H]-piperidyl benzilate employed as the radiolabeled ligand. Our results suggest that the binding of muscarinic agonists to high-affinity sites is characterized by dissociation rate constants higher by two orders of magnitude than those of antagonists and by similar association rate constants. In contrast, the major differences between the kinetic binding parameters of agonists and antagonists to the low-affinity agonist binding sites are in the association rate constants, which were 2 to 5 orders of magnitude lower for agonists. The data demonstrate that isomerization of the muscarinic receptors following ligand binding is insignificant in the case of agonists, unlike that of antagonists. Moreover, as is shown in the medulla-pons preparation, agonist-induced interconversion between high- and low-affinity binding sites does not occur to an appreciable extent.

Acetylcholine↗
PubMed2003

Development of a bisphenol A-adsorbing yeast by surface display of the Kluyveromyces yellow enzyme on Pichia pastoris.

A novel surface-engineered strain of yeast Pichia pastoris was constructed that displays at its surface Kluyveromyces lactis Yellow Enzyme (KYE) fused to the C-terminal half of Saccharomyces cerevisiae alpha-agglutinin. The expression of the fusion protein was controlled by the AOX1-promoter. The new strain showed an increased sorption of the xenoestrogen Bisphenol A (BPA). It was shown that sorption of BPA depended on the presence of methanol in the growth medium and on the pH of the binding assays. The binding kinetics were typical for binding at a surface. The present results demonstrate that the alpha-agglutinin surface display system can be used in the yeast P. pastoris.

Adsorption↗
PubMed1986

Parameter estimation for ligand binding systems kinetics applied to 1,25-dihydroxycholecalciferol.

A mathematical analysis of the kinetics of the hormone-receptor interaction was applied to the 1,25-dihydroxycholecalciferol-intestinal receptor system. The exact analytical solution and the numerical integration of the kinetic equation were installed in a Statistical Analysis System (SAS) computer program to estimate the rate constants of the reaction. Estimates of the parameters obtained by these two methods are similar, demonstrating that the numerical integration can be combined with the nonlinear regression procedure for least-squares parameter fitting using a simple SAS program. This enables estimation of kinetics rate constants when the kinetic equation cannot be solved analytically. The ratio of the rate constants (ka/kd) found by the nonlinear procedure is close to the independently determined equilibrium (Scatchard) constant in the nonlinear analysis.

Animals↗
PubMed1995

1,25-Dihydroxyvitamin D3-induced HL-60 macrophages: regulation of cholesterol and LDL metabolism.

Differentiation of human promyelocytic leukemic HL-60 cells with 1,25-dihydroxyvitamin D3 (D3) results in macrophages which exhibit specific and saturable receptor-mediated processing of both native and modified low density lipoprotein (LDL). Analysis of binding kinetics demonstrated that macrophages bind LDL and acetyl-LDL with similar affinities, yet possess significantly different numbers of receptors (55 +/- 6 x 10(3) LDL receptors/cell vs 79 +/- 7 x 10(3) acetyl-LDL receptors/cell). D3-induced HL-60 macrophages challenged with LDL or acetyl-LDL exhibited suppression of HMG-CoA reductase activity as well as a significant induction in the incorporation of [14C]oleate into cholesteryl ester compared with macrophages incubated with lipoprotein depleted serum. Maximum increases in ACAT activity were obtained in macrophages incubated with 25-hydroxycholesterol plus LDL or acetyl-LDL. The increase in ACAT activity in macrophages challenged with acetyl-LDL paralleled the increase in cellular cholesterol content and the increase of oil red O lipid stainable material, imparting the macrophages with a foamy appearance. The data indicate that D3-induced HL-60 macrophages are a useful model for the study of lipoprotein--macrophage interactions as related to foam cell development and atherogenesis.

Acyl Coenzyme A↗
PubMed1992

HepG2 cells predominantly express the type II interleukin 1 receptor (biochemical and molecular characterization of the IL-1 receptor).

In this study we have characterized the cell surface interleukin 1 (IL-1) receptor in HepG2 hepatoma cells. We found that HepG2 cells bind both IL-1 alpha and beta with high affinity, KDs of 136 and 180 pM and receptor densities of 16,000 and 8500 binding sites/cell respectively. The binding sites appeared to be predominantly type II since phorbol ester treatment of the cells, which selectively downregulates type II IL-1 receptors, reduced binding by 68% while treatment of the cells with an inhibitory monoclonal antibody specific for the type I receptor had no significant effect on IL-1 binding. Competition studies with a modified IL-1 beta analog (Glu4) also revealed binding kinetics more consistent with binding to type II receptors than to type I. Crosslinking and ligand blotting with human 125I-IL-1 demonstrated the presence of two bands, a 78 kDa band typical of crosslinking to type II (p60) receptor, and a 98 kDa band, typical of crosslinking to the type I (p80) receptor. Low level expression of the type I receptor was consistent with molecular biological studies employing polymerase chain reaction (PCR) amplification which indicated that mRNA for the type I receptor was produced by the HepG2 cells. Functional receptors were demonstrated by the induction of IL-8 by IL-1 stimulated cells.

Animals↗
PubMed1996

Effects of Ro 47-0203 and PD155080 on the plasma kinetics, receptor binding and vascular effects of endothelin in the pig.

The effects of the mixed endothelin ET(A)/endothelin ET(B) receptor antagonist Ro 47-0203 (bosentan, 4-tert-butyl-N-[6-(2-hydroxy-ethoxy)-5-( 2-methoxy -phenoxy)-2,2'-bipyrimidin-4-yl] -benzenesulfonamide) and the selective endothelin ET(A) receptor antagonist PD155080 (sodium 2-benzo[1,3]dioxol-5-yl-3-benzyl-4-(4-me thoxy-phenyl)-4-oxobut+ ++-2-enoate) on plasma half-life and regional extraction of exogenous endothelin-1 as well as on the regional vascular effects of endothelin-1 were investigated in the pig in vivo. Bosentan but not PD155080 (5 mg/kg, i.v. bolus, both drugs) increased the arterial plasma levels of endothelin-1-like immunoreactivity. Neither of the drugs affected the plasma half-life of infused endothelin-1. In the spleen, both the extraction and vascular effects of exogenous endothelin-1 were attenuated by both bosentan and PD155080 whereas renal extraction and vascular effects in the kidney were unaffected by both drugs. In the lung, only bosentan decreased pulmonary extraction of endothelin-1. In conclusion, the bosentan-induced increase of circulating endothelin-1 seems to be related to blockade of endothelin-1 binding to endothelin ET(B) receptors. Blockade of these receptors does not influence the overall elimination of endothelin-1, however.

Animals↗
PubMed1991

Interaction of hsp70 with unfolded proteins: effects of temperature and nucleotides on the kinetics of binding.

Circular dichroism and HPLC gel filtration were used to show that cytosolic hsp70 is thermally stable but undergoes a conformational transition (midpoint, 43 degrees C; 57 degrees C in the presence of ATP or ADP) leading to oligomerization. hsp70 binds to unfolded, but not to folded, proteins in a temperature-dependent manner; complex formation is significant only at physiologically relevant temperatures. hsp70 binds ADP more tightly than ATP to form a binary complex, which binds to the unfolded protein more rapidly than free hsp70. ADP also inhibits the ATP-induced dissociation of the hsp70-protein complex. A regulatory role for the hsp70-nucleotide binary complexes is proposed.

Adenosine Diphosphate↗
PubMed2005

Spectroscopic characterization of the isolated heme-bound PAS-B domain of neuronal PAS domain protein 2 associated with circadian rhythms.

Neuronal PAS domain protein 2 (NPAS2) is an important transcription factor associated with circadian rhythms. This protein forms a heterodimer with BMAL1, which binds to the E-box sequence to mediate circadian rhythm-regulated transcription. NPAS2 has two PAS domains with heme-binding sites in the N-terminal portion. In this study, we overexpressed wild-type and His mutants of the PAS-B domain (residues 241-416) of mouse NPAS2 and then purified and characterized the isolated heme-bound proteins. Optical absorption spectra of the wild-type protein showed that the Fe(III), Fe(II) and Fe(II)-CO complexes are 6-co-ordinated low-spin complexes. On the other hand, resonance Raman spectra indicated that both the Fe(III) and Fe(II) complexes contain mixtures of 5-co-ordinated high-spin and 6-co-ordinated low-spin complexes. Based on inverse correlation between nu(Fe-CO) and nu(C-O) of the resonance Raman spectra, it appeared that the axial ligand trans to CO of the heme-bound PAS-B is His. Six His mutants (His266Ala, His289Ala, His300Ala, His302Ala, His329Ala, and His335Ala) were generated, and their optical absorption spectra were compared. The spectrum of the His335Ala mutant indicated that its Fe(III) complex is the 5-co-ordinated high-spin complex, whereas, like the wild-type, the complexes for the five other His mutants were 6-co-ordinated low-spin complexes. Thus, our results suggest that one of the axial ligands of Fe(III) in PAS-B is His335. Also, binding kinetics suggest that heme binding to the PAS-B domain of NPAS2 is relatively weak compared with that of sperm whale myoglobin.

Animals↗
PubMed1984

A 1H nmr study of the amide-bond conformational equilibrium in pirenzepine.

The hindered rotation about the exocyclic amide bond of pirenzepine has been studied using 1H nuclear magnetic resonance spectroscopy. The ratios of the two slowly interconverting conformations (1:1.76 at 2 degrees C and 1:2.37 at 30 degrees C) and the rate of interconversion (1 +/- 0.5 s-1 at 20 degrees C and 247 +/- 20 s-1 at 80 degrees C with delta g ++80 = 71 KJ mol-1) have been measured at various temperatures. The observed rapid rates of interconversion allow us to eliminate the rate of conformational selection of forms II and III as a major contributor to the slow phase of the binding kinetics observed when pirenzepine binds to muscarinic receptors from rat brain (Stockton, Birdsall, Hulme and Burgen, unpublished results).

Amides↗
PubMed1976

A specific FSH receptor in rat granulosa cells: properties of binding in vitro.

The specific binding of [125I]iodoFSH to granulosa cells collected from immature, hypophysectomized, DES-treated rats, was studied in vitro. Specific binding occurred after 5 min and reached maximum after 3 h of incubation at 37 C. Non specific binding was very low (less than 10% of the total binding). The [25I]iodoFSH remained tightly associated with the receptor at pH 7.5, but was rapidly dissociated at pH 5. Unlabeled hFSH competitively inhibited [125I]iodoFSH binding. Kinetic analyses of equilibrium binding experiments gave an apparent association constant (Ka) of 1.34 (+/- 0.31) x 10(10)M-1 [mean (+/- SE)] and a number of binding sites per cell of (NB) 1, 130 +/- 70 (mean +/- SE). Rat prolactin, wheat germ agglutinin, and concanavalin-A did not compete with [125I]iodoFSH, but hLH, hCG, and rTSH competed at doses 300- to 900-fold higher than those of hFSH. Granulosa cells isolated from adult DES-treated rats, as well as cells collected from medium and preovulatory follicles of proestrous rats, gave Ka and NB values similar to those described above. A comparative study of rabbit granulosa cells indicated a much lower binding affinity compared with those from the rat.

Animals↗
PubMedDate not supplied

[3H]-BIBP3226 and [3H]-NPY binding to intact SK-N-MC cells and CHO cells expressing the human Y1 receptor.

We have studied the binding of [3H]-NPY and the newly developed non-peptide Y1 receptor antagonist [3H]-BIBP3226 to intact SK-N-MC cells and CHO-K1 cells transfected with the human NPY Y1 receptor gene i.e. CHO-Y1 cells. Whereas the association and dissociation of the specific [3H]-NPY binding was slow, the binding kinetics of [3H]-BIBP3226 binding was very rapid. Saturation binding of both radioligands reveal the presence of an apparently homogeneous population of high affinity binding sites in both cell lines. The corresponding equilibrium dissociation constants are similar for the two cell lines and are close to those obtained from previous competition binding experiments. The specific binding of both radioligands was completely and with high affinity displaced by BIBP3226 and its inactive (S)-enantiomer BIBP3435 was much less potent. Whilst the NPY Y1 agonists NPY, PYY and [Leu31-Pro34]-NPY completely and potently displaced [3H]-NPY binding, they could only displace 70 to 80% of the [3H]-BIBP3226 binding sites in CHO-Y1 and SK-N-MC cells. A possible explanation can be that only part of the receptors are G-protein coupled. In agreement pertussis toxin was found to reduce high affinity [3H]-NPY binding sites in CHO-Y1 cells whereas [3H]-BIBP3226 binding parameters remained unchanged.

Animals↗