Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “DISSOCIATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources
PubMed1992

Characteristics of the non-exchangeable nucleotide binding sites of mitochondrial F1 revealed by dissociation and reconstitution with 2-azido-ATP.

The dissociation of mitochondrial F1-ATPase with 3 M LiCl at 0 degrees C, followed by reconstitution, has been analysed. FPLC over a gel filtration column in the dissociation buffer revealed the presence of two protein moieties, an alpha 3 gamma delta epsilon complex and single beta-subunits. When the dissociation and chromatography is performed at pH 6.2, the former protein moiety still contains some adenine nucleotides. Reconstitution of the dissociated complex is not possible any more after FPLC, probably due to the loss of residual adenine nucleotides. After a single column centrifugation step one nucleotide per F1 still remains bound. For reconstitution, additional ATP, or a suitable analog, is required. 2-Azido-ATP, but not 8-azido-ATP or ITP, can replace ATP during the reconstitution. F1, reconstituted in the presence of 2-azido-ATP, contains three tightly bound nucleotides, similar to freshly isolated F1, of which in this case one is an adenine nucleotide and two are azido-adenine nucleotides. One of the latter can be rapidly exchanged and is bound to a catalytic site. Covalent binding (at a beta-subunit) of the other tightly bound 2-azido-ATP by ultraviolet illumination does not result in inhibition of the enzyme. Digestion of F1 with trypsin, followed by HPLC, showed that the label is not bound to the fragment containing Tyr-368, nor to the fragment containing Tyr-345. This result was confirmed by CNBr digestion, followed by SDS-urea PAGE. We conclude that during dissociation of F1 one tightly bound nucleotide (ADP) remains bound at an alpha/beta interface site and that for reconstitution binding of ATP to a (non-catalytic) beta-site is required. The conformation of this site differs from that of the two catalytic beta-sites.

Adenosine Triphosphate↗
PubMed1983

Binding of monoclonal antibodies inhibits dissociation but not exchange of HLA and beta 2-microglobulin.

Hyafil and Strominger (Proc Nat Acad Sci USA 76:5834, 1979) showed that the complex of papain-solubilized HLA heavy chain and beta 2-microglobulin (beta 2-m) will measurably dissociate and exchange with free beta 2-m at 37 degrees C but not at 4 degrees C. We have investigated the affects of monoclonal antibodies on these processes. The dissociation reaction at 37 degrees C is inhibited by the presence of HLA-A,B,C specific monoclonal antibodies. Monomorphic antibodies such as BB7.7 against combinatorial determinants are most potent though antibodies against many different determinants of the HLA heavy chain are effective. This suggests that dissociation of beta 2-m from HLA involves a conformational change of the HLA heavy chain which is prevented by antibody binding. BB7.7 also increased the rate of association of HLA heavy chain and beta 2-m. This affect was significantly greater at 37 degrees C and 25 degrees C than at 4 degrees C. Monoclonal antibodies that inhibited dissociation did not inhibit the beta 2-m exchange reaction. If beta 2-m exchange proceeds through a simple dissociation/association reaction then the affect of antibody inhibition on dissociation is almost exactly compensated by its enhancement of association. Alternatively B 2-m exchange may not proceed via a simple dissociation/association reaction.

Antibodies, Monoclonal↗
PubMed1987

Stopped-flow kinetic studies of Ca(II) and Mg(II) dissociation in cod parvalbumin and bovine alpha-lactalbumin.

The dissociation kinetics of complexes of bovine alpha-lactalbumin and cod parvalbumin with Ca(II) and Mg(II) ions induced by mixing of a Ca(II)- or MG(II)-loaded protein with a chelator of divalent cations (EDTA or EGTA) have been studied by means of the stopped-flow method with intrinsic protein fluorescence registration. Within the temperature interval from 10 to approx. 37 degrees C kinetic curves for Ca(II) removal from alpha-lactalbumin are monoexponential with a rate constant ranging from 0.006 to 1 s. Taking into account the rather low rate of fluorescence changes, one can assume that the limiting stage in this case is the dissociation of the single bound Ca(II) ion from the protein and not a conformational transition which occurs after Ca(II) dissociation. At temperatures above 37 degrees C the kinetic curves require at least two exponential terms for a satisfactory fit. The second exponential seems to be due to denaturation of the apo form of alpha-lactalbumin which takes place at these temperatures. The values of the dissociation rate constants for Mg(II) bound to alpha-lactalbumin practically coincide with those for Ca(II). Within the temperature interval 10-30 degrees C the kinetic curves for Ca(II) and Mg(II) removal from parvalbumin are best fitted by a sum of two exponential terms identified as arising from the dissociation of cations from the two binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

A kinetic study of erythrocyte-DNA/anti-DNA immune complex association and dissociation reactions in systemic lupus erythematosus.

Decreased binding capacity of the erythrocyte complement receptor (RBC CR1) in systemic lupus erythematosus (SLE) may contribute to abnormal handling of circulating immune complexes in these patients. Decreased numbers of RBC CR1 have been reported in SLE, but, since binding is a function of both receptor number and receptor binding kinetics, we measured kinetic parameters for the interaction of complement (C) containing [3H]DNA:anti-DNA immune complexes (IC) with normal control (NC) and SLE RBC. Experiments were performed at five temperatures ranging from 7-37 degrees C. The parameters measured included: (1) the maximum quantity of DNA:anti-DNA:C which could bind per RBC, S; (2) the association rate constant, ka, for the binding of DNA:anti-DNA:C to RBC; (3) the dissociation rate constant, kd, for the dissociation of bound DNA:anti-DNA:C IC from RBC; (4) the steady-state constant, Kss (ka/kd); and (5) the energies of activation for association, Eaa, and dissociation, Ead. Although the relative amount of bound DNA:anti-DNA:C per RBC was significantly decreased in SLE patients compared to NC (P less than 0.001), the mean values for Kss, ka, kd, Eaa and Ead did not differ significantly between the two groups. These data suggest the following: (1) RBC CR1 binding and dissociation of DNA:anti-DNA:C are consecutive reactions resulting in steady-state concentrations of free and RBC-bound IC; (2) at steady-state times, the ratio of RBC bound to unbound DNA:anti-DNA:C are governed by kinetic factors; (3) since the binding kinetics of SLE and NC RBC are not significantly different, the decreased binding activity described by other investigators can only be due to a decreased number of CR1 per RBC; and (4) values for Eaa and Ead suggest that the rate-determining steps in IC association with and dissociation from RBC involves making and breaking of hydrogen bonds.

Antibodies, Antinuclear↗
PubMed1988

Recent aspects of the subunit organization and dissociation of hemocyanins.

1. The hemocyanins of the arthropod phylum are built of multiples of hexamers consisting of 1,2,4,6 and 8 of such basic assemblies. Their molecular weights range from about 0.45 x 10(6) to 3.9 x 10(6) daltons. The basic hexameric unit consists of bean-shaped monomers organized in the form of two layers of trimers placed on top of one another. The subunits are heterogeneous, in most cases consisting of four or more electrophoretically different polypeptide chains. 2. Molluscan hemocyanins have an entirely different structure and pattern of assembly from the arthropodan hemocyanins. The basic assembly of the molluscan hemocyanins are decamers organized in the form of right-handed cylinders approximately 300 A in diameter and 140-190 A in height. Different species have one, two and sometimes more than two such assemblies forming correspondingly longer cylindrical particles with molecular weights ranging from about 3.3 x 10(6) to 13 x 10(6) daltons. Cephalopod and chiton hemocyanins consist of single decameric particles, while gastropods have hemocyanins organized of di-decamers or higher assemblies. The subunits of these hemocyanins are elongated protein chains with seven or eight folded globular domains, each housing a binuclear copper center capable of binding and delivering oxygen. 3. The dissociation behavior of the arthropod hemocyanin hexamers and di-hexamers with the hydrophobic urea series of reagents suggest polar and ionic interactions as the main sources of stabilization of the hexamers and the hexamer to hexamer contacts within the di-hexamers. 4. Dissociation studies with the same urea probes with the molluscan hemocyanins, however, suggest a different pattern of stabilization. The stabilization of the decamer to decamer contacts within the gastropod di-decamers appear to be predominantly polar and ionic with relatively few hydrophobic interaction sites. The dimer contacts within the decamers and the monomer to monomer contacts within the dimers observed in the octopus and chiton hemocyanins appear to be predominantly hydrophobic in nature. 5. The urea and the pH dissociation profiles of the single decameric assemblies of some of the octopus and chiton hemocyanins investigated by light-scattering molecular weight methods, have been fitted using either a two-species, decamer to dimer and decamer to monomer scheme of subunit dissociation or a three-species, decamer to dimer to monomer scheme of dissociation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Growth and surface properties of dispase dissociated human fibroblasts.

The dissociation of human fibroblast cultures with the bacterial neutral protease (Dispase II) was monitored by viability and growth measurement and was compared to the effect of trypsin and EDTA. Cell suspensions with high viability and excellent growth were obtained after 10 min incubation at 37 degrees C in 4 U/ml dispase in 0.02% EDTA. A two to three-fold increase in mitotic index occurred in the cultures within 48 h after dispase dissociation. The initial rate of aggregation was comparable to that of trypsin or EDTA dissociated cells, but attachment to a substratum and agglutination by Wheat Germ Agglutinin were markedly enhanced. The results indicate that dispase-EDTA provides a valuable alternative to the enzymatic dissociation with trypsin. Moreover, it is an additional tool for the dissociation of cultured cells and for the study of the surface properties of single cells.

Cell Adhesion↗
PubMed1992

Dissociation of gadolinium chelates in mice: relationship to chemical characteristics.

Tissue distributions of seven 153Gd-labeled Gd chelates were determined at five residence intervals (5 min to 14 days) following intravenous administration of 0.4 mmol/kg to mice. Relationships were sought among physicochemical parameters: thermodynamic and conditional (pH 7.4) equilibrium stability constants (log K and log K'), acid dissociation rate constants (k(obs)), lipophilicity (log P), overall charge, and size (molecular weight). Size and lipophilicity did not correlate with tissue distributions. There were possible correlations between anionic charge and rapid, early renal excretion and between stability constants and long-term residual Gd deposition. Strong correlations (r greater than 0.99) were found between acid dissociation rates and long-term deposition of Gd in the whole body, liver, and femur. This is attributed to dissociation of Gd from the chelates in vivo. Acid dissociation rates may be useful in predicting dissociation of Gd from chelates in vivo.

Animals↗
PubMedDate not supplied

Neonatal seizures: electroclinical dissociation.

Electroclinical dissociation is a phenomenon in which the clinical component of a seizure occurs at times with or without an electrical correlate. The epidemiology of this observation was studied in a neonatal intensive care unit from July, 1983 to December, 1988. Infants demonstrating electroclinical dissociation were compared to those having exclusively electroclinical seizures. Sixteen percent of infants with electrographically-confirmed seizures and 19% of 243 analyzed seizures demonstrated electroclinical dissociation. The two groups revealed very few differences with respect to perinatal factors, etiology, and outcome. The subsequent electroencephalographic background was more disturbed in the electroclinical dissociation group, but did not correlate with clinical outcome. Extremity movements occurred at a statistically significant higher rate during electroclinical seizures. Electroclinical dissociation seizures arise from foci not consistently reflected in surface electrodes.

Brain Diseases↗
PubMed1989

A role of DNA topoisomerases in the active dissociation of DNA minor groove-ligand complexes. A flow cytometric study of inhibitor effects.

The biological effects of a number of DNA ligands which interact with the minor groove of B-form DNA (e.g. netropsin, distamycin and Hoechst 33258) are thought to arise from the direct disturbance of the processes of DNA replication and transcription. Although ligand binding appears to be an important factor in cytotoxicity, the pathways by which drug molecules can be actively dissociated from nuclear DNA are unknown. Recent evidence suggests that minor groove ligands can distort the manner in which DNA associates with nucleosomal core particles and we have hypothesized that in an intact cell such imposed torsional stress could be subject to the action of cellular topoisomerases. We have used flow cytometry to study the effects of various inhibitors (including topoisomerase-interactive drugs) on the responses of a mutant cell line (HoeR415) to Hoechst 33342, given that the mutant shows resistance to the cytotoxicity of this DNA-specific dye due to an enhanced capacity to dissociate nuclear DNA-dye complexes. Ligand-DNA dissociation in the mutant was found to be energy-dependent but not specifically, affected by the drug-efflux blocker verapamil or by inhibitors of DNA synthesis. The topoisomerase II inhibitors novobiocin, VP16, nalidixic acid and the topoisomerase I-interactive drug camptothecin inhibited ligand-DNA dissociation to various extents with novobiocin being the most effective (100% inhibition at 1 mM). Both novobiocin and camptothecin were without effect on the nuclear loss of a DNA intercalator, adriamycin. We conclude that efficient topoisomerase activity is required for the active dissociation of DNA minor groove-ligand complexes.

Animals↗
PubMed2006

Giant extracellular Glossoscolex paulistus Hemoglobin (HbGp) upon interaction with cethyltrimethylammonium chloride (CTAC) and sodium dodecyl sulphate (SDS) surfactants: Dissociation of oligomeric structure and autoxidation.

The effects of two ionic surfactants on the oligomeric structure of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy - form have been studied through the use of several spectroscopic techniques such as electronic optical absorption, fluorescence emission, light scattering, and circular dichroism. The use of anionic sodium dodecyl sulphate (SDS) and cationic cethyltrimethyl ammonium chloride (CTAC) has allowed to differentiate the effects of opposite headgroup charges on the oligomeric structure dissociation and hemoglobin autoxidation. At pH 7.0, both surfactants induce the protein dissociation and a significant oxidation. Spectral changes occur at very low CTAC concentrations suggesting a significant electrostatic contribution to the protein-surfactant interaction. At low protein concentration, 0.08 mg/ml, some light scattering within a narrow CTAC concentration range occurs due to protein-surfactant precipitation. Light scattering experiments showed the dissociation of the oligomeric structure by SDS and CTAC, and the effect of precipitation induced by CTAC. At higher protein concentrations, 3.0 mg/ml, a precipitation was observed due to the intense charge neutralization upon formation of ion pair in the protein-surfactant precipitate. The spectral changes are spread over a much wider SDS concentration range, implying a smaller electrostatic contribution to the protein-surfactant interactions. The observed effects are consistent with the acid isoelectric point (pI) of this class of hemoglobins, which favors the intense interaction of HbGp with the cationic surfactant due to the existence of excess acid anionic residues at the protein surface. Protein secondary structure changes are significant for CTAC at low concentrations while they occur at significantly higher concentrations for SDS. In summary, the cationic surfactant seems to interact more strongly with the protein producing more dramatic spectral changes as compared to the anionic one. This is opposite as observed for several other hemoproteins. The surfactants at low concentrations produce the oligomeric dissociation, which facilitates the iron oxidation, an important factor modulating further oligomeric protein dissociation.

Animals↗
PubMed2003

Small heat shock protein Hsp16.3 modulates its chaperone activity by adjusting the rate of oligomeric dissociation.

Small heat shock proteins usually exist as oligomers and appear to undergo dynamic dissociation/reassociation, with oligomeric dissociation being a prerequisite for their chaperone activities. However, contradictory cases were also reported that chaperone activities could be enhanced with no change or even increase in oligomeric sizes. Using Hsp16.3 as a model system, our studies show the following: (1) Although a preheat (over 60 degrees C) treatment or the presence of low concentrations of urea (around 0.8M) hardly caused any change in the oligomeric size of Hsp16.3 proteins when examined by size exclusion chromatography, its chaperone activities were increased significantly. (2) Further analysis using the unique pore-gradient polyacrylamide gel electrophoresis revealed a dramatic increase in the tendency of oligomeric dissociation for both the preheated and urea-containing Hsp16.3. (3) Meanwhile, for both cases, an apparent increase in the rate constants of oligomeric dissociation was also observed, as determined by utilizing conjugated fluorescence probes whose quantum yield increases accompanying oligomeric dissociation. (4) Moreover, the fluorescence anisotropy analysis also demonstrated that the oligomeric structures for the preheated or urea-containing Hsp16.3 proteins seem to be more dynamic and variable. In light of these observations, we propose that the small heat shock proteins like Hsp16.3 can modulate their chaperone activities by adjusting the rate of oligomeric dissociation in responding to environmental changes. Results obtained here also suggest that small heat shock proteins might be able to "remember" their stress experiences via certain structural alterations which will allow them to act as better chaperones when the stress conditions reappear.

Acetates↗
PubMed2006

pH dependence of the dissociation of multimeric hemoglobin probed by high hydrostatic pressure.

We investigated the thermodynamic features of the classic alkaline dissociation of multimeric hemoglobin (3.1 MDa) from Glossoscolex paulistus (Annelidea) using high hydrostatic pressure. Light scattering measurements up to microscopic thermodynamic equilibrium indicated a high pH dependency of dissociation and association. Electron microscopy and gel filtration corroborated these findings. The volume change of dissociation decreased in absolute values from -48.0 mL/mol of subunit at pH 6.0 to -19.2 mL/mol at pH 9.0, suggesting a lack of protein interactions under alkaline conditions. Concomitantly, an increase in pH reduced the Gibbs free energy of dissociation from 37.7 to 27.5 kJ/mol of subunit. The stoichiometry of proton release calculated from the pressure-induced dissociation curves was +0.602 mol of H(+)/mol of subunit. These results provide a direct quantification of proton participation in stabilizing the aggregated state of the hemoglobin, and contribute to our understanding of protein-protein interactions and of the surrounding conditions that modulate the process of aggregation.

Dimerization↗
PubMed2006

Spermidine inhibits transient and stable ribosome subunit dissociation.

Recent light-scattering experiments and sucrose density gradient centrifugational analyses suggested that the 70S ribosome undergoes RRF- and EF-G-triggered transient subunit dissociation that is followed by IF3-induced stable dissociation. However, the experimental conditions did not include the ubiquitous cellular polyamine spermidine, which is required for efficient translation. We found that when spermidine was present, the transient dissociation was inhibited. Moreover, the published experiments used ribosome concentrations that were far lower than the physiological concentration. We found that when spermidine and higher ribosome concentrations were included in the experimental conditions, only very limited stable subunit dissociation was observed. These results suggest that neither transient nor stable dissociation occurs under physiological conditions applied here.

Dose-Response Relationship, Drug↗
PubMed2005

Fundamental studies on the intermediate layer of a bipolar membrane part IV. Effect of polyvinyl alcohol (PVA) on water dissociation at the interface of a bipolar membrane.

This paper investigates the effect of polyvinyl alcohol (PVA) as the intermediate layer of bipolar membranes on water dissociation. The bipolar membranes are prepared by coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers, which had been immersed in PVA aqueous solutions with different concentrations in advance. The experimental results show that the effect of PVA on water dissociation is significantly affected by its concentration: at low concentration range PVA solution catalyzes water dissociation and at high concentration range PVA solution shows a retardant effect. The phenomenon is different from the situation where polyethylene glycol (PEG) is used as the intermediate layer. Based on the adsorption data and the measurements of X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy, it is found that (1) the effect of PVA concentration on water dissociation can be explained by the competition and compromise of two effects--the catalytic and hydrophilic effect of the PVA molecule and the steric effect of the enlargement of junction thickness; (2) the reason that at high concentration range PVA and PEG show different effects on water dissociation is that the junction thickness is enlarged excessively by PVA, which is based on the intrinsic characteristics of PVA molecules.

Journal Article↗
PubMed2005

Pressure-jump NMR study of dissociation and association of amyloid protofibrils.

The dissociation and reassociation processes of amyloid protofibrils initiated by pressure-jump have been monitored with real-time (1)H NMR spectroscopy using an intrinsically denatured disulfide-deficient variant of hen lysozyme. Upon pressure-jump up to 2 kbar, the matured protofibrils grown over several months become fully dissociated into monomers within a few days. Upon pressure-jump down to 30 bar, the dissociated monomers immediately start reassociating. The association and dissociation cycle can be repeated reproducibly by alternating pressure, establishing a notion that the protofibril formation is simply a slow kinetic process toward thermodynamic equilibrium. The outstanding simplicity and effectiveness of pressure in controlling the protofibril formation opens a new route for investigating mechanisms of amyloid fibril-forming reactions. The noted variation in the pressure-induced dissociation rate with the progress of the association reaction suggests multiple mechanisms for the elongation of the protofibril. The disulfide-deficient hen lysozyme offers a particularly simple model system for thermodynamic and kinetic studies of protofibril formation as well as for screening drugs for amyloidosis.

Amyloid↗
PubMed2003

Monitoring hydrate formation and dissociation in sandstone and bulk with magnetic resonance imaging.

Magnetic resonance imaging (MRI) has been shown to be a very effective tool for monitoring the formation and dissociation of hydrates because of the large intensity contrast between the images of the liquid components and the solid hydrate. Tetrahydrofuran/water hydrate was used because the two liquid components are miscible and form hydrate at ambient pressure. These properties made this feasibility study proceed much faster than using methane/water, which requires high pressure to form the hydrate. The formation and dissociation was monitored first in a THF/water-saturated Berea sandstone plug and second in the bulk. In both cases it appeared that nucleation was needed to begin the formation process, i.e., the presence of surfaces in the sandstone and shaking of the bulk solution. Dissociation appeared to be dominated by the rate of thermal energy transfer. The dissociation temperature of hydrate formed in the sandstone plug was not significantly different from the dissociation temperature in bulk.

Chemical Phenomena↗
PubMed2005

Enhanced excitability of dissociated primary sensory neurons after chronic compression of the dorsal root ganglion in the rat.

A chronic compression of the dorsal root ganglion (CCD) produces ipsilateral cutaneous hyperalgesia and allodynia in rats. Intracellular electrophysiological recordings from formerly compressed neurons in the intact dorsal root ganglion (DRG) reveal lower than normal current thresholds (CTs) and abnormal spontaneous activity (SA) (Zhang JM, Song XJ, LaMotte RH. Enhanced excitability of sensory neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion. J Neurophysiol 1999;82:3359-66). To determine if the neuronal hyperexcitability is intrinsic to the soma, L4 and L5 DRG neurons from rats that had prior CCD surgery or those that did not (controls) were dissociated, and intracellular recordings obtained 3-8 h (acute) or 24-30 h (1d) after culture. The CTs of large- (>45 microm diameter) and medium- (30 approximately 45 microm) sized neurons from control rats after acute or 1d culture were similar to those formerly recorded from the intact DRG and significantly lower for CCD than for control rats. However, the CTs of small- (<or=30 microm) sized neurons from control rats were significantly lower in acute or 1d culture groups than they were in the intact DRG and not significantly different from those of dissociated small neurons from CCD rats. The overall incidence of SA was higher for CCD than for control neurons after 1d culture (10.3 vs. 1.8%) and similar to that obtained in the intact DRG. We conclude that the CCD-induced hyperexcitability of medium- and large-sized neurons remains after dissociation and is intrinsic to the soma. For small-sized neurons, the effects of CCD observed in the intact DRG are less apparent after dissociation possibly due to the hyperexcitability produced by the dissociation process itself.

Action Potentials↗
PubMed1983

pH dependence of dissociation of the ovine prolactin rabbit mammary receptor complex.

Ovine prolactin specifically bound to rabbit mammary membrane prolactin receptor was rapidly dissociated in a pH dependent manner with 0.1M ammonium acetate. Up to 75% of the bound hormone was dissociated at pH 4.0 or lower in less than 5 minutes. The pK of the dissociation was 4.7, implicating one or more critical carboxyl groups. Exposure of the membrane bound receptor to the dissociating buffer for up to one hour did not reduce its ability to bind hormone. The dissociated hormone was characterized as intact ovine prolactin by Bio-Gel P-150 gel chromatography and by its ability to bind to fresh rabbit prolactin receptor with the same binding affinity as native hormone.

Animals↗