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R J Ellis

Publications and source records attributed to R J Ellis.

At least 91 records · Page 5Linked to original sources
PubMed1991

Chemical synthesis of 10 kDa chaperonin. Biological activity suggests chaperonins do not require other molecular chaperones.

Molecular chaperones are required for the correct folding and assembly of certain other polypeptides. It is not known whether molecular chaperones themselves require other chaperones to become functional. A 97-amino acid chaperone, the chaperonin 10 protein was chemically synthesised so that during synthesis and purification there was no contact of the chaperone with any other protein. The purified, synthetic chaperonin 10 protein formed oligomeric structures spontaneously and was biologically active as a chaperonin. This is the first description of a chemically synthesised chaperonin, and suggests that no other chaperones are required for correct folding, polymerisation and biological activity of this chaperone.

Bacterial Proteins↗
PubMed1990

Quantitative computed tomography of the brain with xenon enhancement: a phantom study with the GE9800 scanner.

A recently proposed application of quantitative computed tomography is in the study of cerebral blood flow and partition coefficient using stable xenon as a freely diffusible, radio-opaque tracer. Central to the method is the calibration factor describing the relationship between CT number and xenon concentration in the brain. In this paper we examine the influence of temporal fluctuations, kVp, radial position and beam hardening on this calibration factor through the analysis of a series of phantom measurements. We conclude that under clinically realistic conditions and with correlations for temporal fluctuations, the error associated with the calibration factor is less than 2%. Furthermore, errors of this magnitude translate into errors of less than 3% in derived blood flow and partition coefficient values obtained using xenon-enhanced computed tomography.

Brain↗
PubMed1990

Dichotic asymmetries in aging and alcoholic subjects.

It has been suggested that certain cognitive changes found both with aging and with chronic alcoholism are accompanied by alterations in hemispheric functional asymmetries. One prevalent view states that these well-delineated cognitive changes are directly related to a selective disruption of right hemisphere function. The present study tested this hypothesis using dichotic listening measures of functional asymmetry. Both alcoholics and older nonalcoholics evidenced patterns of cognitive preservation and impairment similar to those seen in patients with known right hemisphere dysfunction. Nevertheless, dichotic listening findings did not reveal any selective effect on the right hemisphere, as previously proposed. The dichotic studies supported the view that both hemispheres are affected by aging and alcoholism. Patients with right hemisphere lesions demonstrated characteristic and predictable changes in dichotic asymmetries, illustrating the reliability of the dichotic measures as indices of hemispheric function.

Adult↗
PubMed1990

The molecular chaperone concept.

Molecular chaperones are a ubiquitous family of cellular proteins which mediate the correct folding of other polypeptides, and in some cases their assembly into oligomeric structures, but which are not components of those final structures. Known chaperones do not possess steric information for protein folding but inhibit unproductive folding and assembly pathways which would otherwise act as dead-end kinetic traps and produce incorrect structures. Chaperones function by binding specifically and non-covalently to interactive protein surfaces that are exposed transiently during cellular processes such as protein synthesis, protein transport across membranes, DNA synthesis, the recycling of clathrin cages, the assembly of organellar complexes from imported subunits, and stress responses. This binding is reversed under circumstances which favour correct interactions and in some cases ATP hydrolysis is involved in this reversal. Some chaperones bind specifically to a structural feature present in a wide range of unrelated proteins that is accessible only during the early stages of folding. The nature of this structural feature is unknown, but its identification is an important goal of current research. Knowledge of chaperone function may be important for the production of proteins for biotechnological purposes since in some cases chaperones may improve the yield of functional product. It is likely that chaperone diseases exist which result from the failure of certain proteins to fold correctly due to changes in chaperone structure.

Binding Sites↗
PubMed1989

Molecular chaperones: proteins essential for the biogenesis of some macromolecular structures.

Many polypeptides can self-assemble into functional structures while others assemble only in the presence of additional proteins (molecular chaperones) which are not components of the final structure. We discuss here the effect that the recognition of the essential roles played by these proteins in assembly processes may have on the principle of spontaneous self-assembly.

Animals↗
PubMed1989

Alcoholism, aging, and functional cerebral asymmetries.

Reviews research concerning the possible relationship between cognitive decline and abnormal hemispheric asymmetries in alcoholic and aging individuals. Because the deteriorative effects of alcoholism on the central nervous system have suggested greater visuospatial than language-related functional impairments, numerous investigators had hypothesized that right-hemisphere integrity may be selectively disrupted (rather than the left hemisphere). Furthermore, performance on diverse perceptual and cognitive tests used to measure right-hemisphere functions in alcoholics had been observed to decline with normal chronological aging as well, thereby raising the possibility that certain neuropsychological deficits associated with alcoholism (presumably related to right-hemispheric decline) are identical to those associated with aging. However, an extensive review of empirical research findings on cerebral asymmetries both in alcoholics and in aging individuals suggested that their patterns of functional laterality are similar to those of normal controls.

Age Factors↗
PubMed1989

The molecular chaperone concept.

Molecular chaperones are a ubiquitous family of proteins whose proposed role is to mediate the folding and assembly of other proteins into oligomeric structures. The essential function of molecular chaperones is to prevent the formation of incorrect structures which may result from the transient exposure of charged or hydrophobic surfaces normally involved in interactions between or within polypeptide chains. Such transient exposure may occur during the synthesis of polypeptides, the unfolding and refolding that occurs during their transport across membranes, the association of polypeptides made in one subcellular compartment with those made in another, changes in protein-protein interactions during the normal functioning of a complex, and recovery from stresses such as heat shock. Three classes of molecular chaperone are discussed: the nucleoplasmins, the BiP group, and the chaperonins.

Bacterial Proteins↗
PubMed1988

Homologous plant and bacterial proteins chaperone oligomeric protein assembly.

An abundant chloroplast protein is implicated in the assembly of the oligomeric enzyme ribulose bisphosphate carboxylase-oxygenase, which catalyses photosynthetic CO2-fixation in higher plants. The product of the Escherichia coli groEL gene is essential for cell viability and is required for the assembly of bacteriophage capsids. Sequencing of the groEL gene and the complementary cDNA encoding the chloroplast protein has revealed that these proteins are evolutionary homologues which we term 'chaperonins'. Chaperonins comprise a class of molecular chaperones that are found in chloroplasts, mitochondria and prokaryotes. Assisted post-translational assembly of oligomeric protein structures is emerging as a general cellular phenomenon.

Adenosine Triphosphatases↗
PubMed1987

Dissociation of the ribulosebisphosphate-carboxylase large-subunit binding protein into dissimilar subunits.

The ribulosebisphosphate-carboxylase large-subunit binding protein from Pisum sativum chloroplasts is an oligomer of two types of subunit with the composition alpha 6 beta 6. These two subunits are immunologically distinct, show different partial protease digestion patterns and have different amino-terminal sequences. Leaves of Hordeum vulgare also contain an oligomeric binding protein composed of equal amounts of two types of subunit. Treatment of either P. sativum stromal extracts or purified binding protein with ATP and Mg2+ ions causes the dissociation of the oligomeric form of the binding protein to the monomeric subunits. This effect is highly specific for ATP since CTP, UTP, GTP, ADP, AMP, cyclic AMP, NADPH and pyrophosphate do not cause dissociation.

Adenosine Triphosphate↗
PubMed1987

Cognitive deficits related to memory impairments in alcoholism.

Cognitive impairments related to alcoholism are examined in terms of input, intervening, and output variables. Respectively, the dysfunctions are represented by visuospatial/perceptual abnormalities, affective/conative deficits, and strong perseverative response tendencies. Defects in one or more of these aspects of cognitive functioning may appear as problems of memory. Functional differences between subgroups of alcoholics who do and do not develop severe anterograde amnesia characteristic of Korsakoff's syndrome presumably are attributable to differences in the distribution and extent of brain pathology. Both subgroups have widespread cortical pathology, which may play an important role in stimulus-processing deficiencies observed in both. Korsakoff's have demonstrated a more significant degree of pathology in diencephalic and basal forebrain structures than that observed in non-Korsakoff alcoholics; this may contribute to the greater memory and affective impairments in the former. However, in no subgroup of alcoholics can a single functional system or brain region be implicated as the major contributory factor. Rather, damage to multiple brain regions likely is responsible for the plethora of cognitive difficulties reported in the alcoholism literature.

Alcohol Amnestic Disorder↗
PubMed1987

Comparison of fluence-response relationships of phototropism in light- and dark-grown buckwheat.

Fluence-response relationships of phototropism in light- and dark-grown buckwheat (Fagopyrum esculentum Moench.) were compared using systematically varied fluence rates and irradiation times of unilateral monochromatic blue light. Etiolated seedlings respond to most fluence rates in a tri-phasic manner. Phase one differs from classic first positive in that reciprocity is not observed and the peak occurs at a wide variety of fluences, often orders of magnitude less than those characteristic of first positive. Light-grown plants display this pattern only when stimulated by low fluence rates. Phase three is an ascending arm directly related to irradiance time and is comparable to classic second positive. Phase two is a nearly indifferent zone separating phases one and three. At the lowest fluence rates, the maximal observed curvature is greater for dark-grown than for light-grown plants and the former curve more in response to short (2-second) exposures than do the latter. At the highest fluence rates, the maximal observed curvature is much greater for light-grown than for dark-grown seedlings, particularly at irradiation times of 2 to 3 minutes or more. Tropic curvatures correlate positively with increasing fluence rate up to some inflection range, above which the relationship becomes negative. This inflection range is approximately two orders of magnitude higher for light-grown plants.

Journal Article↗