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Biomedical subjects

B E Wright

Publications and source records attributed to B E Wright.

At least 73 records · Page 4Linked to original sources
PubMed1978

Placoid pigment epitheliopathy and Harada's disease.

Twenty-six patients are described who suffered from acute bilateral multifocal pigment epithelial disease. In 7 the pattern of disease was indistinguishable from acute posterior multifocal placoid pigment epitheliopathy, while in 8 it was indistinguishable from Harada's disease. In a further 9 cases the pigment epithelial disease was associated with serious detachment of the retina simulating Harada's disease but without systemic symptoms; spontaneous resolution occurred within a few days, and there was no recurrence. One additional case had short-lived disease with detachment initially, but this was followed by severe recurrence, and the last patient had serious detachment in 1 eye but not the other. When seen as a whole these patients appeared to represent a continuous spectrum of disease making it difficult to define boundaries between one condition and another. The difficulties in distinguishing diseases according to morphology alone are emphasised.

Diagnosis, Differential↗
PubMed1977

Fourth expansion and glucose perturbation of the Dictyostelium kinetic model.

The kinetic model of carbohydrate metabolism has been expanded to include: (a) the accumulation of alpha and beta-cellulose, insoluble cell-wall glycogen and mucopolysaccharide; (b) the role of RNA turnover as a source of carbon for end-product synthesis and as a buffer regulating the level of uridine nucleotides in this metabolic network; and (c) the role of purine-nucleoside phosphorylase, 5'-AMP nucleotidase, nucleosidediphosphate kinase and polynucleotide phosphorylase. One of many predictions based on this model is that cells differentiating in the presence of glucose will produce sorocarps with an abnormally high trehalose to cellulose ratio. External perturbation of either the model or of developing cells by glucose increases the levels of sorocarp trehalose and glycogen, 5-fold and 6-fold respectively. Evaluation of the experimental data and the simulation analyses have allowed several predictions to be made concerning the compartmentation of metabolites and the permeability of cells to glucose during differentiation.

Carbohydrate Metabolism↗
PubMed1976

Glycogen phosphorylase in Dictyostelium discoideum. I. Purification and properties of the enzyme.

The glycogen phosphorylase of Dictyostelium discoideum has been purified over 200-fold from cells in the culmination stage of development. Analytical gel electrophoresis of the purified enzyme indicates one major protein band with a molecular weight of approximately 210,000. Gel elution verified the presence of phosphorylase activity associated with the protein band. Electrophoresis of partially purified extracts prepared from amoebae cells revealed the absence of phosphorylase protein. Sodium dodecyl sulfate electrophoresis on 6% gels indicated that the purified phosphorylase is composed of subunits, 95,000 in molecular weight. The purified enzyme exhibited normal Michaelis-Menten kinetics and activity was not stimulated by added nucleotides such as 5'-AMP. Nucleotide sugars (GDP-glucose, UDP-glucose, ADP-glucose) were competitive inhibitors of the phosphorylase reaction.

Dictyostelium↗
PubMed1976

Glycogen phosphorylase in Dictyostelium discoideum. II. Synthesis and degradation during differentiation.

A purified preparation of glycogen phosphorylase from Dictyostelium discoideum was used to elicit specific antisera in rabbits. The antisera were used to quantitate the amount of precipitable phosphorylase protein from cell extracts prepared at various stages of the developmental cycle. Following isotope incorporation studies in differentiating cells, the specific radioactivity of enzyme isolated by antibody precipitation was compared to that of acid-insoluble protein. Prior to 5 hours of development, glycogen phosphorylase could not be detected enzymatically or immunologically. Between aggregation and culmination, the rate of enzyme synthesis increased about 6-fold, then decreased to an insignificant value in young sorocarps. The rate of enzyme degradation was negligible during the period of maximal enzyme accumulation, then increased to a peak value of 40% after culmination, coincident with a rapid drop in phosphorylase activity. The data indicated that the increase in glycogen phosphorylase activity during development results from an increase in the rate of enzyme synthesis.

Dictyostelium↗
PubMed1975

Mathematical modeling of differentiation in Dictyostelium discoideum.

Methods for the dynamic analysis of biochemical differentiation are presented. These are demonstrated in the analysis of biochemical differentiation of the carbohydrate system in D. discoideum. Procedures for simplification which are presented are projection and contraction of the system trajectory in state space and the generation of reduced equivalent dynamic metabolic networks. The importance of the hierarchical structure of differentiating systems is discussed and the concept of a dynamic embedding diagram is introduced. It is shown that complex systems must be analyzed on an epoch by epoch basis, each epoch being a period of time characterized by a constant dynamic embedding diagram, and that widely different time scales and state space scales may be necessary in different epochs. In particular there is no a priori lower limit to the time scale which may be necessary during the analysis. Some problems in mathematically defining differentiation are discussed.

Carbohydrate Metabolism↗
PubMed1975

An analysis of the kinetic positions held by five enzymes of carbohydrate metabolism in Dictyostelium discoideum.

The role of five enzymes essential to differentiation in Dictyostelium discoideum has been analyzed by simulation studies and ranked with respect to their over-all effect on the conversion of glycogen to cellulose and trehalose in the later stages of differentiation. Their order is, in decreasing effectiveness, (a) glycogen phosphorylase, (b and c) cellulose and trehalose synthetase, (d) UDP-glucose pyrophosphorylase and (e) glycogen synthetase. Glycogen phosphorylase controls the speed of differentiation, which can also be slightly modified by the level of glycogen synthetase. The cellulose and trehalose synthetases and UDP-glucose pyrophosphorylase control the relative concentrations of trehalose and cellulose. The final trehalose to cellulose ratio is also affected by the speed of differentiation. Compensatory interaction between enzymes affecting the outcome of differentiation is also analyzed.

Cellulose↗