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Dissociation and childhood trauma in psychologically disturbed adolescents.

OBJECTIVE: To test the hypothesis that dissociation in adolescence is positively correlated with stress or abuse experienced earlier, the authors assessed dissociation in a heterogeneous group of disturbed adolescents and examined the relationship between the degree of dissociation and the degree of reported childhood stress, abuse, or trauma. METHOD: The subjects were 47 adolescents, 13-17 years old, who were institutionalized for periods of 1-13 weeks in a private mental hospital; 35 were girls and 12 were boys. Participants completed the Dissociative Experiences Scale and a child abuse and trauma questionnaire. The hospital records of 40 of the 47 adolescents were also available. RESULTS: Scores on the Dissociative Experiences Scale correlated significantly with self-reported physical abuse or punishment, sexual abuse, psychological abuse, neglect, and negative home atmosphere but not with abuse ratings made from hospital records. CONCLUSIONS: Together with the authors' previous work showing a relation between childhood stress and later dissociation in normal college students, these findings support the view that dissociation represents a reaction to early negative experience and places multiple personality disorder at the extreme end of a continuum of dissociative sequelae of childhood trauma. Researchers should continue to try to identify psychiatric patients with prominent dissociative characteristics or symptoms and attempt to correlate this phenomenology with negative earlier experiences.

Adolescent↗

Dissociative disorders in psychiatric inpatients.

OBJECTIVE: This study attempted to determine 1) the prevalence of dissociative disorders in psychiatric inpatients, 2) the degree of reported childhood trauma in patients with dissociative disorders, and 3) the degree to which dissociative experiences are recognized in psychiatric patients. METHOD: A total of 110 patients consecutively admitted to a state psychiatric hospital were given the Dissociative Experiences Scale. Patients who scored above 25 were matched for age and gender with a group of patients who scored below 5 on the scale. All patients in the two groups were then interviewed in a blind manner, and the Dissociative Disorders Interview Schedule, the Traumatic Antecedent Questionnaire, and the posttraumatic stress disorder (PTSD) module of the Structured Clinical Interview for DSM-III-R, Nonpatient Version, were administered. Chart reviews were also conducted on all patients. RESULTS: Fifteen percent of the psychiatric patients scored above 25 on the Dissociative Experiences Scale; 100% of these patients met DSM-III criteria for a dissociative disorder. These patients had significantly higher rates of major depression, PTSD, substance abuse, and borderline personality than did the comparison patients, and they also reported significantly higher rates of childhood trauma. Chart review data revealed that dissociative symptoms were largely unrecognized. CONCLUSIONS: A high proportion of psychiatric inpatients have significant dissociative pathology, and these symptoms are underrecognized by clinicians. The proper diagnosis of these patients has important implications for their clinical course.

Adolescent↗

Dissociation in aging Holocaust survivors.

OBJECTIVE: This study explored relationships among dissociation, trauma, and posttraumatic stress disorder (PTSD) in elderly Holocaust survivors with and without PTSD and in a demographically comparable group of nontraumatized subjects. METHOD: Holocaust survivors with PTSD (N = 35) and without PTSD (N = 25) who had been recruited from the community and a comparison group (N = 16) were studied. Dissociation was evaluated with the Dissociative Experiences Scale. Past cumulative trauma and recent stress were evaluated with the Antonovsky Life Crises Scale and the Elderly Care Research Center Recent Life Events Scale, respectively. PTSD symptoms were assessed with the Clinician-Administered PTSD Scale. RESULTS: The Holocaust survivors with PTSD showed significantly higher levels of current dissociative experiences than did the other groups. However, the extent of dissociation was substantially less than that which has been observed in other trauma survivors with PTSD. Dissociative Experiences Scale scores were significantly associated with PTSD symptom severity, but the relation between Dissociative Experiences Scale scores and exposure to trauma was not significant. CONCLUSIONS: Possible explanations for this finding include the age of the survivors, the length of time since the traumatic event, and possible unique features of the Holocaust survivor population. Nevertheless, the findings call into question the current notion that PTSD and dissociative experiences represent the same phenomenon. The findings suggest that the relationships among dissociation, trauma, and PTSD can be further clarified by longitudinal studies of trauma survivors.

Age Factors↗

Dissociation as a mediator of psychopathology among sexually abused children and adolescents.

OBJECTIVE: This study investigated the role of dissociation as a mediator of mental health outcomes in children with a history of sexual abuse. METHOD: The study group consisted of 114 children and adolescents (ages 10-18 years) who were wards of the Illinois Department of Children and Family Services and were living in residential treatment centers. Interviews, provider ratings, and chart reviews were used to assess the relationship of childhood abuse history, dissociative responses, and psychopathology. RESULTS: Sexual abuse history was significantly associated with dissociation, whereas a history of physical abuse was not. Both sexual abuse and dissociation were independently associated with several indicators of mental health disturbance, including risk-taking behavior (suicidality, self-mutilation, and sexual aggression). Severity of sexual abuse was not associated with dissociation or psychopathology. Analysis of covariance indicated that dissociation had an important mediating role between sexual abuse and psychiatric disturbance. These results were replicated across several assessment sources and varied perspectives. CONCLUSIONS: The findings suggest a unique relationship between sexual abuse and dissociation. Dissociation may be a critical mediator of psychiatric symptoms and risk-taking behavior among sexually abused children. The assessment of dissociation among children may be an important aspect of treatment.

Adolescent↗

The role of panic in acute dissociative reactions following trauma.

OBJECTIVE: 'Peritraumatic dissociation' refers to alterations in awareness and memory for events that occur during and shortly after a traumatic experience. Despite the prevalence of reported peritraumatic dissociation, little is known about the mechanisms that mediate dissociative responses in the initial period after trauma. One theory suggests that peritraumatic dissociation may be a response to elevated arousal and panic symptoms during trauma. This study investigated panic symptoms that occurs at the time of the trauma and their relationship to ongoing dissociation in acute stress disorder. DESIGN: A sample of traumatized people with acute stress disorder or controls were administered a range of psychopathology measures within one month of their trauma. METHOD: Fifty-one civilian trauma survivors with either acute stress disorder or no acute stress disorder were administered the acute stress disorder interview, the Impact of Event Scale, the Beck Anxiety Inventory, the Peritraumatic Dissociative Experiences Questionnaire, and the Physical Reactions Scale to index panic reactions during the trauma. RESULTS: Hierarchical regression analysis found that panic reactions during the trauma accounted for nearly half of the variance (47%) of peritraumatic dissociation, and subsequent stress reactions accounted for an additional 3% of the variance. CONCLUSIONS: These findings are consistent with proposals that acute dissociation is associated with panic symptoms that occur during the traumatic experience. Possible mechanisms for the association of panic and dissociation are discussed.

Adult↗

Psychometric validation of the State Scale of Dissociation (SSD).

Although dissociative phenomena are often transient features of mental states, existing measures of dissociation are designed to measure enduring traits. A new present-state self-report measure, sensitive to changes in dissociative states, was therefore developed and psychometrically validated. Fifty-six items were formulated to measure state features, and sorted according to seven subscales: derealization, depersonalization, identity confusion, identity alteration, conversion, amnesia and hypermnesia. The State Scale of Dissociation (SSD) was administered with other psychiatric scales (DES, BDI, BAI, SCI-PANSS) to 130 participants with DSM-IV major depressive disorder schizophrenia, alcohol withdrawal, dissociative disorders and controls. In these sample populations, the SSD was demonstrated as a valid and reliable measure of changes in and the severity of dissociative states. Discriminant validity, content, concurrent, predictive, internal criterion-related, internal construct and convergent validities, and internal consistency and split-half reliability were confirmed statistically. Clinical observations of dissociative states, and their comorbidity with symptoms of depression and psychotic illness, were confirmed empirically. The SSD, an acceptable, valid and reliable scale measuring state features of dissociation at the time of completion, was obtained. This is a prerequisite for further investigation of correlations between changes in dissociative states and concurrent physiological parameters.

Adult↗

Evaluating the neuropsychological dissociation evidence for multiple memory systems.

This article presents a critical evaluation of the logic and nature of the neuropsychological dissociation evidence that has provided one of the essential lines of support for claims of multiple memory systems--specifically, suggesting that amnesia selectively compromises, and an intact hippocampal system selectively supports, a particular form of memory. An analysis of the existing neuropsychological dissociation evidence is offered in which different classes of evidence--different dissociation approaches-are identified and characterized. The logic of these neuropsychological dissociation approaches is evaluated critically in terms of their ability to distinguish among alternative theoretical views. We conclude that although they support a multiple memory systems account, the findings from these types of neuropsychological dissociation, taken individually and without support from other converging lines of cognitive neuroscience evidence, cannot definitively rule out alternative formulations. A more powerful neuropsychological dissociation approach is then outlined, involving dissociation within condition, that, by more effectively limiting the critical domains of difference between the dissociated performances, can successfully rule out alternative accounts. Its application in Ryan, Althoff, Whitlow, and Cohen (2000) is described, providing strong support for the power of the dissociation within condition approach.

Cognitive Science↗

A DFT study of the adsorption and dissociation of CO on Fe(100): influence of surface coverage on the nature of accessible adsorption states.

In the present article, we report adsorption energies, structures, and vibrational frequencies of CO on Fe(100) for several adsorption states and at three surface coverages. We have performed a full analysis of the vibrational frequencies of CO, thus determining what structures are stable adsorption states and characterizing the transition-state structure for CO dissociation. We have calculated the activation energy of dissociation of CO at 0.25 ML (ML = monolayers) as well as at 0.5 ML; we have studied the dissociation at 0.5 ML to quantify the destabilization effect on the CO(alpha3) molecules when a neighboring CO molecule dissociates. In addition, it is shown that the number and nature of likely adsorption states is coverage dependent. Evidence is presented that shows that the CO molecule adsorbs on Fe(100) at fourfold hollow sites with the molecular axis tilted away from the surface normal by 51.0 degrees. The asorprton energy of the CO molecule is -2.54 eV and the C-O stretching frequency is 1156 cm(-1). This adsorption state corresponds to the alpha3 molecular desorption state reported in temperature programmed desorption (TPD) experiments. However, the activation energy of dissociation of CO(alpha3) molecules at 0.25 ML is only 1.11 eV (approximately 25.60 kcal mol(-1)) and the gain in energy is -1.17 eV; thus, the dissociation of CO is largely favored at low coverages. The activation energy of dissociation of CO at 0.5 ML is 1.18 eV (approximately 27.21 kcal mol(-1)), very similar to that calculated at 0.25 ML. However, the dissociation reaction at 0.5 ML is slightly endothermic, with a total change in energy of 0.10 eV Consequently, molecular adsorption is stabilized with respect to CO dissociation when the CO coverage is increased from 0.25 to 0.5 ML.

Journal Article↗

BIRD (blackbody infrared radiative dissociation): evolution, principles, and applications.

Blackbody infrared radiative dissociation (BIRD) describes the observation of ion-dissociation reactions at essentially zero pressure by the ambient blackbody radiation field, which is usually studied in the ion-trapping ion cyclotron resonance (ICR) mass spectrometer. A brief summary of the historical context and evolution is provided. Focussing on the quantitative observation of the temperature dependence of BIRD rates, methods are developed for connecting BIRD observations with activation parameters and dissociation thermochemistry. Three regimes are differentiated and described, comprising large molecules, small molecules, and intermediate-sized molecules. The different approaches to interpreting BIRD kinetics in those three regimes are discussed. In less than a decade since its inception, this approach to studying gas-phase ions has spread over a wide variety of applications, which are surveyed. Some major areas of activity are: the characterization of solvent-molecule detachment from solvated ions; dissociation reactions of biomolecules (polypeptides, oligonucleotides, complexes involving polysaccharides) and the structural information to be deduced from them; and dissociations of proton-bound and metal-ion-containing complexes. Studies of blackbody-radiation-driven evaporation of water molecules from large water-cluster ions are surveyed briefly. Several techniques related to BIRD are noted, including collisional dissociation in the FT-ICR ion trap; high-pressure thermal dissociation in quadrupole ion traps and in heated inlet capillary regions; hot-filament-assisted dissociation; and infrared multiphoton dissociation (IRMPD).

Kinetics↗

A comparison of solid intraventricular and dissociated intraparenchymal fetal substantia nigra grafts in a rat model of Parkinson's disease: impaired graft survival is associated with high baseline rotational behavior.

It has been established that substantia nigra (SN) grafts can produce a behavioral effect in animal models of Parkinson's disease when transplanted either into the lateral ventricles as solid tissue fragments or directly into the striatum as dissociated cells. These two transplantation methods (solid-intraventricular and dissociated-intraparenchymal) were directly compared in the present study. Adult male rats received unilateral SN lesions by stereotaxic injection of 6-hydroxydopamine. Fetal ventral mesencephalon, containing the SN, was harvested from 15-day gestational rat fetuses. Equal weights of tissue were transplanted, either as solid-intraventricular or dissociated-intraparenchymal grafts. In the animals with surviving grafts, similar decreases in apomorphine-induced rotational behavior were seen in both dissociated (40.2% at 6 weeks, 29.6% at 12 weeks, N = 12) and solid (31.8% at 6 weeks, 51.0% at 12 weeks, N = 11) graft groups. Control animals receiving tectal grafts showed smaller decreases (dissociated: 12.6% at 6 weeks, 18.8% at 12 weeks, N = 20; solid: 4.1% at 6 weeks, 8.0% at 12 weeks, N = 20). There were no significant overall differences between the effects of the solid and dissociated grafts; however, in the subgroup of animals with high baseline levels of rotational behavior, the solid-intraventricular grafts produced a significantly larger effect then did the dissociated-intraparenchymal SN grafts. There was also a tendency for the effect of the solid-intraventricular grafts to increase gradually over the 12-week testing period, whereas the effects of the dissociated-intraparenchymal grafts were maximal by 6 weeks after transplantation. For both SN graft groups, there were significant correlations between decreases in rotation and numbers of surviving tyrosine hydroxylase-immunoreactive neurons in the grafts. It was also found that animals with no surviving transplanted tyrosine hydroxylase-positive neurons had higher baseline levels of rotational behavior. Therefore, in the present model, solid-intraventricular and dissociated-intraparenchymal SN grafts have similar effects on apomorphine-induced rotational behavior, except that the solid-intraventricular grafts tended to produce a larger effect in animals with high baseline levels of rotational behavior.

Animals↗

A Predictive Approach Using Fractal Analysis for Analyte-Receptor Binding and Dissociation Kinetics for Surface Plasmon Resonance Biosensor Applications.

A predictive approach using fractal analysis is presented for analyte-receptor binding and dissociation kinetics for biosensor applications. Data taken from the literature may be modeled, in the case of binding using a single-fractal analysis or a dual-fractal analysis. The dual-fractal analysis represents a change in the binding mechanism as the reaction progresses on the surface. A single-fractal analysis is adequate to model the dissociation kinetics in the examples presented. Predictive relationships developed for the binding and the affinity (k(diss)/k(bind)) as a function of the analyte concentration are of particular value since they provide a means by which the binding and the affinity rate coefficients may be manipulated. Relationships are also presented for the binding and the dissociation rate coefficients and for the affinity as a function of their corresponding fractal dimension, D(f), or the degree of heterogeneity that exists on the surface. When analyte-receptor binding or dissociation is involved, an increase in the heterogeneity on the surface (increase in D(f)) leads to an increase in the binding and in the dissociation rate coefficient. It is suggested that an increase in the degree of heterogeneity on the surface leads to an increase in the turbulence on the surface owing to the irregularities on the surface. This turbulence promotes mixing, minimizes diffusional limitations, and leads subsequently to an increase in the binding and in the dissociation rate coefficient. The binding and the dissociation rate coefficients are rather sensitive to the degree of heterogeneity, D(f,bind) (or D(f1)) and D(f,diss), respectively, that exists on the biosensor surface. For example, the order of dependence on D(f,bind) (or D(f1)) and D(f2) is 6.69 and 6.96 for k(bind,1) (or k(1)) and k(2), respectively, for the binding of 0.085 to 0.339 µM Fab fragment 48G7(L)48G7(H) in solution to p-nitrophenyl phosphonate (PNP) transition state analogue immobilized on a surface plasmon resonance (SPR) biosensor. The order of dependence on D(f,diss) (or D(f,d)) is 3.26 for the dissociation rate coefficient, k(diss), for the dissociation of the 48G7(L)48G7(H)-PNP complex from the SPR surface to the solution. The predictive relationships presented for the binding and the affinity as a function of the analyte concentration in solution provide further physical insights into the reactions on the surface and should assist in enhancing SPR biosensor performance. In general, the technique is applicable to other reactions occurring on different types of biosensor surfaces and other surfaces such as cell-surface reactions. Copyright 2000 Academic Press.

Journal Article↗

[Comparison between dissociated and associated heterophoria].

BACKGROUND: Since Ogle (1949) dissociated heterophoria is distinguished from associated heterophoria. Dissociated heterophoria is defined as a deviation from the orthovergence position that occurs when no fusional contours are provided. Associated heterophoria is a deviation that occurs under prism correction of fixation disparity, i.e. under a viewing condition in which fusional contours are absent only in the centre of the visual field. Both dissociated and associated heterophoria have been used as indications for prismatic correction. It has been controversially discussed to what extent dissociated and associated heterophoria are comparable. METHODS: A total of 43 subjects were investigated using the white Maddox rod test for horizontal dissociated heterophoria and the cross test of Hans-Joachim Haase (a test similar to the fixation disparity test described by Ogle 1949) for horizontal associated heterophoria. In both tests subjects were asked to continually correct any deviation using Herschel prisms. Readings were taken after 1 min. RESULTS: The correlation between the results obtained with the white Maddox rod test and the cross test was r = 0.89 (p < 0.0001) and the slope of the regression line was 0.92 (95% confidence interval from 0.77 to 1.07). One subject was unable to reach a match in the cross test because she had an "obligate" fixation disparity due to a staphyloma posticum. CONCLUSIONS: Our study revealed a high correlation between dissociated and associated heterophoria. This result appears plausible since the feedback loop for fusion is disconnected in both cases, although in a different manner: When dissociated heterophoria is measured, fusionable contours are absent. When associated heterophoria is measured, any disparity of peripheral contours that could serve as an error signal is nullified by instantaneous prism correction. The high concordance of dissociated and associated heterophoria suggests that both measures are of equal value as an indication for prismatic spectacle correction. In rare cases of an "obligate" fixation disparity, however, associated heterophoria cannot be determined so that dissociated heterophoria remains as the only indication.

Adult↗

The dissociation of the extracellular hemoglobin of Tubifex tubifex at extremes of pH and its reassociation upon return to neutrality.

The dissociation of the extracellular hemoglobin of Tubifex tubifex at alkaline and acid pH, and its reassociation upon return to neutral pH, was investigated using gel filtration, ultracentrifugation, and polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE). Tubifex hemoglobin dissociated at pH above 8 and below 6; both dissociations appeared to be equilibrium processes. The extent of dissociation increased as the pH moved away from neutrality; although dissociation was virtually complete at pH 11, its extent at acid pH did not exceed 50-60% at pH 4. Ca(II), Mg(II), and Sr(II) cations over the range 1-100 mM decreased the extent of the dissociation only at alkaline pH. The visible absorption spectrum of the oxyhemoglobin remained unaltered in the pH range 4-9. At more extreme pH, it changed with time, altering irreversibly to that of the aquo ferri form. Gel filtration of the hemoglobin at both extremes of pH showed that it dissociated into two heme-containing fragments; one consisting of subunit 1 (Mr approximately 17,000) and the other containing subunits 2, 3, and 4 of the hemoglobin (Mr approximately 60,000). Upon return to neutral pH, the dissociated fragment reassociated to the extent of 50 to 80% to whole hemoglobin molecules. The reassociation decreased with increase in alkaline pH, and with decrease in acid pH to which the hemoglobin had been exposed; it increased in the presence of Ca(II), Sr(II), and Mg(II) only subsequent to dissociation at alkaline pH. The SDS-PAGE patterns, gel-filtration elution volumes, and alpha-helical contents, determined from circular dichroism at 222 nm, of the reassociated whole molecules were identical to those of the native hemoglobin.

Animals↗

The effect of alkaline earth cations and of ionic strength on the dissociation of earthworm hemoglobin at alkaline pH.

1. The effect of alkaline earth cations on the dissociation of the extracellular hemoglobin of Lumbricus terrestris and the effect of ionic strength on the dissociation of the hemoglobins of L. terrestris and Tubifex tubifex at concentrations of ca 2.5 mg/ml, over the pH range 9.0-10.5 was investigated using ultracentrifugation to separate the dissociated from the undissociated molecules. 2. Mg(II), Ca(II) and Sr(II) at concentrations of up to 0.2 M, decreased the dissociation of Lumbricus oxyhemoglobin from 70% at pH 9.0 and 100% at pH 9.5 and higher, to 20-30% at 0.05 M. The three cations were equally effective in decreasing the extent of dissociation of L. terrestris oxyhemoglobin over the pH range 9.0-10.5, with a K1/2 of ca 10 mM. 3. The dissociation of L. terrestris oxyhemoglobin over the pH range 9.0-10.5 was decreased only to 50-60% in the presence of up to 0.5 M NaCl or KCl; there was no further decrease in dissociation at concentrations of the two salts up to 1.5 M. 4. The dissociation of T. tubifex oxyhemoglobin over the pH range 9.0-10.0 was decreased from 100% to ca 40-50% in the presence of 0.5 M NaCl or KCl with little or no change at higher concentrations. At pH 10.5 and 11.0 the decrease in dissociation was more gradual, reaching ca 50% at 1.5 M NaCl.

Animals↗

The dissociation rate of estrogen receptor-ligand complexes is increased by high concentrations of steroids and antiestrogens.

The first-order dissociation rate constant, k-, of estradiol from uterine estrogen receptor, measured kin the presence of micromolar concentrations of diethylstilbestrol, increased linearly over a large concentration range (0-300 microM) of diethylstilbestrol. The experimental K- measured appears to be the sum of a basal dissociation rate constant corresponding to the spontaneous dissociation in the absence of diethylstilbestrol, and a diethylstilbestrol-induced dissociation rate constant, which is proportional to both the diethylstilbestrol concentration and the inverse of the cytosol concentration. Diethylstilbestrol induced the dissociation of estradiol in all species studied (lamb, calf and rat) and of estrone and 2 antiestrogens in lamb uterus. Various steroids and triphenylethylene antiestrogens also efficiently induced the dissociation of estradiol from the estrogen receptor. However, the potency of these inducers, which varied greatly, was not correlated with the binding affinity for the estrogen receptor. Structural characteristics and the hydrophobicity of the inducers, however, did appear to be important parameters. The relative efficiency of inducers varied depending on the ligand that was bound to the receptor. This induced dissociation allows the complete dissociation of estrogen receptor-[3H]-ligand complexes in a short time (less than 24 h) at low temperatures without alteration of the level of [3H] ligand bound non-specifically and can therefore be used to measure the [3H] ligand bound to the receptor by exchange at 0-4 degree C. From the specificity and the high doses of inducers required to make possible the observation of a significant effect, we conclude that the induced dissociation probably does not have a biological role.

Animals↗

pH-dependent receptor/ligand dissociation as a determining factor for intracellular sorting of ligands for epidermal growth factor receptors in rat hepatocytes.

Both epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) bind to EGF receptors and TGF alpha has been reported to be more potent than EGF as far as many biological effects are concerned. One possible reason for this is thought to be the difference in their dissociation from the receptors in intracellular acidic compartments, which may affect the final pathway (lysosomal degradation or recycling to cell-surface) of endocytosed ligands. This study was aimed at clarifying the relationship between intracellular dissociation from the receptors and the fate of the endocytosed ligands. First, (125)I-human EGF (hEGF), mouse EGF (mEGF), or human TGF alpha (hTGF alpha) was prebound to cell-surface receptors or intracellularly preloaded, followed by further incubation at 37 degrees C in primary cultured rat hepatocytes. In these experiments, the magnitude of the dissociation rate constant (k(off)) of each ligand at pH 6.0, which is similar to that inside early endosomes, was found to be in the following order: hTGF alpha>mEGF>hEGF. The recycled portion of endocytosed ligands was also in the order: hTGF alpha>mEGF>hEGF. Digitonin treatment of preloaded cells revealed that the intracellular dissociation of hTGF alpha was more rapid than that of hEGF. Moreover, several histidine-inserted or -deleted hEGF mutants were prebound to rat liver sinusoidal membrane vesicle, followed by further incubation at 37 degrees C. The dissociation rate of histidine-deleted hEGF mutants was less rapid than that of hEGF itself. These results suggested that efficient dissociation in the earlier intracellular compartment leads the endocytosed ligands to be recycled to the cell surface whereas late dissociation results in intracellular degradation in hepatocytes. Thus, one possible strategy to improve their stability in the circulation may be a change in intracellular ligand/receptor dissociation with a minimal effect on the affinity for receptors on the cell-surface and histidine residues may partly contribute to the pH-sensitive dissociation.

Animals↗

The dissociation rate of estrogen receptor alpha from the consensus estrogen response element.

The rate of dissociation of recombinant, purified human estrogen receptor alpha (ERalpha) from a fluorescein-labeled DNA containing the consensus vitellogenin ERE sequence (F-vitERE) was determined in real time using fluorescence anisotropy. The complex of estradiol-occupied ERalpha with F-vitERE had an apparent dissociation rate of 1.48+/-0.06x10(-2) s(-1) and a half-life of 46.6 s at room temperature. The dissociation rate was characterized by a single exponential decay, suggesting that ER dissociates from the DNA as a preformed dimer, rather than as two individual monomers. The association rate of estradiol-occupied ERalpha for the F-vitERE was calculated as 7x10(6) M(-1) s(-1) based on the dissociation rate measured and previous determinations of the equilibrium dissociation constant (Kd) in similar assay conditions (Ozers et al., 1997). In buffer containing various concentrations of salt, the rate of dissociation of estradiol-occupied ERalpha from F-vitERE was accelerated by increasing salt concentrations. Compared to estradiol-occupied ERalpha, the rate of dissociation of unoccupied ERalpha from the F-vitERE was very similar, indicating that estradiol occupancy does not affect the dissociation rate of ERalpha from the ERE.

Binding, Competitive↗

Kinetics of the dissociation of indium-(p-substituted-benzyl)ethylenediaminetetraacetic acid hapten analogues from the monoclonal anti-hapten antibody CHA255.

Half-lives were measured for the dissociation of a series of 20 indium-benzyl-EDTA derivatives from a monoclonal antibody that binds to them. Most haptens gave expected monoexponential dissociation curves with half-lives ranging from approximately 8 to approximately 100 min at 22 +/- 1 degree C. Precise (+/- approximately 2.5%) determinations were made using centrifugal ultrafiltration to separate free from bound hapten. A strong pH dependence of the dissociation half-life was found for the two haptens studied. Activation enthalpies were identical (23 +/- 1 kcal/mol) for the dissociation of four haptens, suggesting that, in contrast to individual rate constants, this parameter is insensitive to hapten modification. The dissociation half-lives provided evidence for the location of a positive charge in the binding site, but gave no clear indication of the role of hydrophobic interactions or of steric requirements in hapten binding. While variations in ionic strength had no effect on the dissociation rate, lowering surface tension with dioxane increased the rate somewhat. Three hapten-antibody complexes showed biexponential dissociation rates. It is postulated that this results from distinct conformations of the complex dissociating at different rates. The dissociation rate constant was found to be an extremely sensitive indicator of the hapten-antibody interaction that can be measured very precisely.

Albumins↗