SEARCH · Search PubMed

Results for “Crowding”

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.

SourceResearch connectionFrom yearThrough year

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

At least 469 records · Page 26Linked to original sources

PubMedDate not supplied

Applications of time-resolved resonance energy transfer measurements in studies of the molecular crowding effect.

The native structures of many globular proteins are only weakly stabilized and form in solution ensembles of multiple conformers. The energy differences between the conformers are assumed to be small. This is the case of flexible multidomain proteins where domain motions were observed. High concentrations of inert macrosolute, which create a crowded or confined environment, can cause shifts of the distribution of the conformers of such proteins towards the more compact structures. This effect may also promote compact structures in partially folded proteins. Time-resolved dynamic non-radiative excitation energy transfer (tr-RET) is suitable for detection of either subtle or major changes in distributions of intramolecular distances in protein molecules in solutions. Two experiments were performed which demonstrated the applicability of tr-RET for detection of the effect of macrosolutes on the conformational ensembles of flexible states of protein molecules. The distribution of distances between residues 203 and 169 in the CORE domain of E. coli adenylate kinase (AK) in the denatured state was determined in the presence of high concentrations of dextran 40. A significant shift of the mean of the distribution was observed without reduction of its width. This was interpreted as a shift to compact structure without change of the degree of disorder of the chain. In a second experiment the distribution of the distance between residues 55 and 169 in AK, which spans the cleft between the CORE and the AMPbind domains, was monitored. No clear effect of high concentrations of dextran 40 was found. These experiments show the strength of the application of tr-RET in investigation of changes in the sub-states of flexible conformations of globular protein. Networks of pairs of labeled sites can be prepared and tr-RET experiments can be performed in order to search for the segments of the protein molecules, which respond to the presence of inert macromolecules in their environment.

Adenylate Kinase↗

PubMedDate not supplied

Non-ideal tracer sedimentation equilibrium: a powerful tool for the characterization of macromolecular interactions in crowded solutions.

Non-ideal tracer sedimentation equilibrium is a technique devised to quantify the effect of high concentrations of unrelated macromolecules on the self- or hetero-associations of dilute macromolecules. Principles and experimental techniques are reviewed, and previous experimental work summarized. A new analysis of experimental data is presented that requires no a priori assumptions regarding the nature of weak repulsive interactions between solute species and the concentrated (crowding) species.

Animals↗

PubMed1992

Charisma, crowd psychology and altered states of consciousness.

This paper argues that an interpretive meaning-centered analysis is not adequate for understanding collective behavior that is outside the range of calculating rationality. Alternative approaches to collective irrational action are drawn from the work of Weber and Durkheim, as well as from the crowd psychologists Le Bon and Tarde. These approaches are then illustrated in a short analysis of the trajectories and recruitment techniques of two contemporary American religious annunications: est and Scientology, and the findings applied to the general social formation.

Consciousness↗

PubMed1992

Macromolecular crowding and volume perception in dog red cells.

To differentiate whether the primary volume signal in dog red cells arises from a change in cell configuration or the concentration and dilution of cell contents, we prepared resealed ghosts that had the same surface area and hemoglobin concentration as intact cells but less than 1/3 their volume. Shrinkage of both intact cells and resealed ghosts triggered Na/H exchange. Activation of this transporter in the two preparations correlated closely with cytosolic protein concentration but not at all with volume. The Na/H exchanger was more sensitive to shrinkage in albumin-loaded resealed ghosts than in intact cells or ghosts containing only hemoglobin. Similar results were obtained for the swelling-induced [K-Cl] cotransporter. We believe perception of cell volume originates with changes in cytoplasmic protein concentration. We think the kinases and phosphatases that control the activation of membrane transporters in response to cell swelling or shrinkage are regulated by the mechanism of macromolecular crowding.

Animals↗

PubMed2004

Biomechanics of the dental arch and incisal crowding.

During horizontal contact, the dental arch represents a link chain in which two convex articular surfaces are in contact and are tensioned by the dentogingival and dentoalveolar fibrous tissue. Joints composed of convex-convex surfaces are equivalent to stretched dimeric link chains whose links are in a mechanically unstable position under compression. Experiments on plaster models show that the dimensional stability of an articulated (dental) arch is considerably increased when a concave and a convex articular surface are in contact, as these joints are equivalent to an overlapping dimeric link chain whose links are in a mechanically stable position when under compression. In the abraded denture of Stone Age man, horizontal interdental contacts of transversally concave-convex dental surfaces may be found extending even into the incisal region. Increased stability of the dental arch and reduced problems of incisal crowding are to be expected if an overlapping dimeric chain is produced morphologically in each horizontal contact by means of slight interproximal enamel reduction.

Alveolar Process↗

PubMed2006

Effect of colour pop-out on the recognition of letters in crowding conditions.

The crowding effect of adjacent objects on the recognition of a target can be reduced when target and flankers differ in some feature, that is irrelevant to the recognition task. In this study, the mechanisms of this effect were explored using targets and flankers of the same and different colours. It was found that facilitation nearly equal to that of differently coloured targets and flankers can be observed with a differently coloured background blob in the location of the target. The different-colour effect does not require advance knowledge of the target and flanker colours, but the effect increases in the course of three trials with constant mapping of colours. The results are consistent with the notion of exogenous attention that facilitates the processing at the most salient locations in the visual field.

Color Perception↗

PubMed2005

Effects of crowding on the thermal stability of heterogeneous protein solutions.

Crowding can substantially affect the transition of a protein between its native (N) and unfolded (U) states via volume exclusion effects. Also, it influences considerably the aggregation (A) of unfolded proteins. To examine the details, we developed an approach for computing the kinetic rates of the process N <--> U --> A in which the concentration of the protein is explicitly taken into account. We then compute the relative change with temperature of the protein denaturation for various fractional volume occupancies and partition of proteins in solution. The analysis indicates that, in protein solutions in which the average distance between proteins is comparable with the radius of gyration of an unfolded protein, steric effects increase the stability of the proteins which are in compact, native states. In heterogeneous protein solutions containing various types of proteins with different thermal stabilities, the unfolding of the most thermolabile proteins will increase the stability of the other proteins. The results shed light on the way proteins change the thermal stability of a cell as they unfold and aggregate. This study may be valuable in questions related to the dynamics of thermal injuries.

Animals↗

PubMed2005

Influence of osmolytes on inactivation and aggregation of muscle glycogen phosphorylase b by guanidine hydrochloride. Stimulation of protein aggregation under crowding conditions.

The effects of the osmolytes trimethylamine-N-oxide (TMAO), betaine, proline, and glycine on the kinetics of inactivation and aggregation of rabbit skeletal muscle glycogen phosphorylase b by guanidine hydrochloride (GuHCl) have been studied. It is shown that the osmolytes TMAO and betaine exhibit the highest protective efficacy against phosphorylase b inactivation. A test system for studying the effects of macromolecular crowding induced by osmolytes on aggregation of proteins is proposed. TMAO and glycine increase the rate of phosphorylase b aggregation induced by GuHCl.

Animals↗

PubMed1990

An examination of the crowding hypothesis in epileptic patients who have undergone the carotid amytal test.

Epileptic patients who had undergone the carotid amytal test were assessed on a variety of measures of verbal and non-verbal ability. All patients had left hemisphere dysfunction of early onset. Patients with atypical speech patterns performed as well as patients with left hemisphere speech on most, though not all, measures of language function. Transfer of language to the right hemisphere, however, occurred at a heavy cost. Patients with atypical speech patterns performed more poorly than their left hemisphere speech counterparts on a wide variety of non-verbal tests. These results are discussed in terms of the "crowding" hypothesis.

Adolescent↗

PubMed1995

13C-NMR off-resonance rotating frame spin-lattice relaxation studies of bovine lens gamma-crystallin self association: effect of 'macromolecular crowding'.

The NMR technique of 13C off-resonance rotating frame spin-lattice relaxation, which provides an accurate assessment of the effective rotational correlation time (tau 0, eff) for macromolecular rotational diffusion, was applied to the study of gamma-crystallin association as a function of protein concentration and temperature. Values of the effective rotational correlation time for gamma-crystallin rotational diffusion were obtained at moderate to high protein concentrations (80-350 mg/ml) and at temperatures above, and below, the cold cataract phase transition temperature. With increasing concentration gamma-crystallin was observed to increasingly associate as reflected by larger values of tau 0, eff Decreasing temperature in the range of 35 to 22 degrees C was found to result in no change in the temperature corrected value of tau 0, eff at a gamma-crystallin concentration of 80 mg/ml, whereas at temperatures of 18 degrees C or below, this parameter was approx. twofold larger, suggesting the occurrence of a well defined phase transition, which correlated well with the cold cataract phase transition temperature. At higher protein concentrations, by contrast, tau 0, eff (temperature corrected) was found to increase by approx. 1.6- to 2-times in the temperature interval 35 degrees C to 22 degrees C, a result consistent with the dependence of the cold cataract phase transition temperature on gamma-crystallin concentration. Analysis of intensity ratio dispersion curves, using an assumed model of isodesmic association, permitted the estimation of the association constant characterizing the aggregation under particular conditions of concentration and temperature. The significant increase in the value of the association constant with moderate increases in protein concentration was rationalized by invoking the effect of 'macromolecular crowding'. The results obtained in this study suggest that in the intact lens, where high protein concentrations prevail, gamma-crystallin is unlikely to be found in the monomeric state, but more likely, as a significantly aggregated species, representing a broad molecular weight distribution.

Animals↗

PubMed1995

Crowding-induced organization of cytoskeletal elements. III. Spontaneous bundling and sorting of self-assembled filaments with different flexibilities.

The typical cell contains ca. 25 vol.-% protein, of which ca. 10% forms cytoskeletal filaments and ca. 90% is non-aggregating globular protein. It has previously been theoretically predicted that, under such highly crowded conditions, rigid filaments will coalesce into tight bundles coexisting with an isotropic solution of globular proteins. In the present work we show that such spontaneous bundling will occur even when filament flexibility is taken into account because the persistence length of the filaments is much longer than the diameter of the globular proteins. The theoretical results are consistent with experimentally observed bundling of F-actin (the most flexible of the three most common types of cytoskeletal filaments) in the presence of globular macromolecules.The main effect of increased filament flexibility on bundling is to cause somewhat looser packing. In mixtures of filaments, differences in flexibilities can lead to segregation. This segregation is accentuated when the stiffer filament is also wider. The results suggest that actin filaments and microtubules will spontaneously form segregated bundles in the presence of cellular concentrations of globular proteins. While cross-linking proteins may serve to stabilize these bundles, their more important function in bundling may be to fine tune the structure (e.g., polarity and registration of filaments).

Cytoskeletal Proteins↗

PubMed1977

Glycogen synthase in the rat tapeworm, Hymenolepis diminuta--I. Enzyme activity during development and with crowding.

1. Activity of glycogen synthase (E.C. 2.4.1.11) in Hymenolepis diminuta (Cestoda: Cyclophyllidea) was investigated as a function of development and with crowding. 2. Synthase activity was low in the anterior and posterior ends of the worms and highest in the pregravid proglottids in the mid-portion of the strobila. 3. The enzyme activity increased during development of the cestode at least up to 15 days postinfection, but the increase in activity apparently was not due to conversion of the inactive to the active form. 4. Mature oncospheres also contained glycogen synthase, but the activity was lower than in strobilar tissues. 5. Synthase I activities and the proportion of total activity in the I form were generally higher in worms from high density (100 worm) infections than in those from low density (10 worm) infections.

Animals↗

PubMed1991

Indolamines in the cockroach Blaberus craniifer Burm. nervous system--I. Fed and crowded young females.

1. Indolamine levels were determined in the cerebral ganglion, the thoraco-abdominal nerve cord (except the last ganglion), and the 6th abdominal ganglion of females of Blaberus craniifer. 2. Measurements were made at the imaginal molt and on fed and crowded imagos at 10, 20 and 30 post-imaginal days. 3. Indolamines were found in the nervous system of young females, but 5-hydroxytryptophan was only detected in the thoraco-abdominal nerve cord. 4. Amine levels were related to the age of the cockroach, particularly during this period, to post-ecdysis events and ootheca formation.

Animals↗

PubMed2006

Relapse of anterior crowding in patients treated with extraction and nonextraction of premolars.

INTRODUCTION: The purpose of this study was to evaluate long-term stability of incisor crowding in orthodontic patients treated with and without premolar extractions. METHODS: Dental casts and cephalometric records of 98 patients were evaluated before treatment (T1), at posttreatment (T2), and at postretention (T3). Half of the patients had been treated with extractions, and half were treated nonextraction. RESULTS: Irregularity, as measured by the irregularity index, decreased 5.51 mm in the extraction group and 2.38 mm in the nonextraction group. Mandibular incisor irregularity increased 0.97 mm in the extraction group and 0.99 mm in the nonextraction group, respectively, in the postretention period. Maxillary incisor irregularity relapse was smaller than mandibular incisor relapse for both groups. Intercanine width expanded during treatment. At T3, mandibular intercanine width decreased in both groups, but the differences were not statistically significant. At T3, intermolar width was stable, arch depth decreased, overbite and overjet slightly increased, SN mandibular plane angle decreased, and incisor positions in both groups tended to return to T1 values. Clinically acceptable stability was obtained. CONCLUSIONS: With the exception of the interincisal angle, no statistically significant differences were recorded between the extraction and nonextraction groups from T2 to T3. No statistically significant correlations were found between any variables studied and mandibular incisor irregularity at T1, T2, and T3.

Adolescent↗

PubMed2005

Crowded and sparse domains in object recognition: consequences for categorization and naming.

Some models of object recognition propose that items from structurally crowded categories (e.g., living things) permit faster access to superordinate semantic information than structurally dissimilar categories (e.g., nonliving things), but slower access to individual object information when naming items. We present four experiments that utilize the same matched stimuli: two examine superordinate categorization and two examine picture naming. Experiments 1 and 2 required participants to sort pictures into their appropriate superordinate categories and both revealed faster categorization for living than nonliving things. Nonetheless, the living thing superiority disappeared when the atypical categories of body parts and musical instruments were excluded. Experiment 3 examined naming latency and found no difference between living and nonliving things. This finding was replicated in Experiment 4 where the same items were presented in different formats (e.g., color and line-drawn versions). Taken as a whole, these experiments show that the ease with which people categorize items maps strongly onto the ease with which they name them.

Adult↗

PubMed2005

The effects of social anxiety and depression on the evaluation of facial crowds.

Facial crowds of emotion connoting approval or criticism are linked to the fears of socially anxious individuals. We examined evaluation ratings and decision latencies of mixed facial displays by individuals with generalized social phobia (GSPs, n = 18), individuals with comorbid depression and GSP (COMs, n = 18), and normal controls (CONs, n = 18). First, we postulated that GSPs will assign more negative ratings to predominantly disapproving audiences as compared to CONs, and that GSPs will be faster in their evaluation of these audiences (negative bias hypothesis). Second, we expected depression, but not social anxiety, to be associated with diminished positive evaluation of audiences containing predominantly happy expressions and with a slower processing of such positive cues (the impaired positivity hypothesis). Results supported the negative bias hypothesis, and provided partial support for the impaired positivity hypothesis. The importance of examining the processing of complex non-verbal cues in social anxiety and in depression is discussed.

Adult↗

PubMed2005

Synthesis of sterically crowded derivatives of anomeric pairs of D-glucose disaccharides.

Derivatization of carbohydrates is of considerable interest since the derivatives can be used for structural studies in the field of mass spectrometry. We report here the synthesis of a series of sterically crowded derivatives of various linkage and stereo-isomeric glucose-glucose disaccharides with the impetus being to understand the effect of these derivatized groups on fragmentation of the glycosidic bond and the development of methodology for discernment of the anomeric configuration. The synthesis of per-alkylated (methyl, ethyl, propyl, butyl, and pentyl), per-esterified (acetyl, pivaloyl, mesitoyl), and per-silylated (tert-butyl-dimethyl silyl) glucose--glucose disaccharide derivatives has been reported.

Acetylation↗

PubMed2005

Space in systems biology of signaling pathways--towards intracellular molecular crowding in silico.

How cells utilize intracellular spatial features to optimize their signaling characteristics is still not clearly understood. The physical distance between the cell-surface receptor and the gene expression machinery, fast reactions, and slow protein diffusion coefficients are some of the properties that contribute to their intricacy. This article reviews computational frameworks that can help biologists to elucidate the implications of space in signaling pathways. We argue that intracellular macromolecular crowding is an important modeling issue, and describe how recent simulation methods can reproduce this phenomenon in either implicit, semi-explicit or fully explicit representation.

Algorithms↗