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Biomedical subjects

A Wilkinson

Publications and source records attributed to A Wilkinson.

At least 109 records · Page 6Linked to original sources
PubMed1982

The dissociation of glucose oxidase by sodium n-dodecyl sulphate.

1. The enzymic activity of glucose oxidase was determined as a function of pH and sodium n-dodecyl sulphate (SDS) concentration. 2. Glucose oxidase is not deactivated by SDS at pH 6 even after prolonged incubation, but is deactivated at pH 4.3 and 3.65. 3. Sedimentation-rate analysis showed that glucose oxidase dissociates into its two subunits at pH 5 and below, and sedimentation-equilibrium experiments in the presence of SDS gave a subunit molecular weight of 73,500. 4. SDS binds to glucose oxidase in acid solutions; specific binding occurs ap pH 3.65, but at pH 6 only co-operative binding was observed. 5. Glucose oxidases in which some of the carboxy groups were blocked with glycine methyl ester were deactivated by SDS at pH 6.0; the rate of deactivation increased with the extent of esterification. 6. Deactivation of esterified glucose oxidases correlated with thermal analysis of the initial SDS interaction, the exothermicity of the interaction increasing with the extent of esterification. 7. The results show that carboxy groups confer resistance to deactivation by SDS on glucose oxidase by screening cationic residues and inhibiting specific interactions that facilitate dissociation into subunits.

Amino Acids↗
PubMed1981

The influence of age on the hypothalamo-neurohypophyseal system of the mouse: a quantitative ultrastructural analysis of the posterior pituitary.

A quantitative ultrastructural study of the posterior pituitary was undertaken. The posterior pituitary is the storage of the hormones vasopressin and oxytocin. Female C57BL/Icrfat mice which were under conditions of normal hydration were sampled at 8 and 32 months of age. There was a slight age-related decline in the volume fraction of cellular components with a corresponding increase in perivascular space. The proportion of neurosecretory endings and swellings showing autophagic activity (Dellman type II Herring bodies) increased significantly in the senescent mouse. The total pituicyte population showed a significant decrease in volume fraction, but with a significant increase in electron-dense types. Of the subcellular parameters examined, only the diameter of the neurosecretory granules showed a significant age-related decrease, the volume fraction remaining unaltered. The animals used in this study were from stocks found to be in a constant oestrus-metoestrus-like state unlikely to obscure changes in pituitary morphology. Over-all, the morphology of the posterior pituitary of the senescent female mouse under physiologically defined resting conditions indicates maintenance of the status quo.

Aging↗
PubMed1978

The influence of age and dementia of the neurone population of the mammillary bodies.

In a study on the influence of age and senile dementia on the mammillary bodies, the medial mammillary nucleus was examined in 15 brains from young (control), normal aged and demented females. Neurone populations, volumes and cell densities were estimated. Individual variation was high in all the groups studied. Normal ageing and dementia were accompanied by a substantial loss of volume but no significant loss of neurones, resulting in a considerable increase in cell density. No significant differences were detectable between the normal aged group and the demented group. These findings are in agreement with other investigators who have found no neuronal loss with age in discrete nuclear structures.

Adult↗
PubMed1978

Precursor keratin protein from human epidermis.

Prekeratin has been isolated from human epidermis using the method of Matoltsy for bovine nose epidermis. Analysis by sedimentation equilibrium indicates that human prekeratin is heterogeneous in solution. The molecular weight range is from about 200 X 10(3) to at least 2 X 10(6). Polyacrylamide gel electrophoresis shows three polypeptide chains of molecular weights 65,000 60,000 and 58,000. A lower than average ratio of polar/apolar amino acid residues suggests that hydrophobic interactions are important for stability.

Amino Acids↗
PubMed1978

Schooling, environment, and cognitive development: a cross-cultural study.

The purpose of this study was to investigate the influence of schooling and general environmental conditions on the development of memory and cognitive skills in young children. The subjects were 824 5- and 6-year-old children living in jungle villages and in slum settlements of Lima, Peru. Half of the children in both the jungle and city were Mestizo, and half were Quechua Indians. Some 6-year-olds of each cultural group and in each location attended school; others did not. Memory tasks were presented in different modes of representation, that is, verbal, pictorial, and enactive; and cognitive tasks in "concrete" and "abstract" versions. A sample of parents in each group was interviewed concerning environmental conditions. In addition, samples of upper-middle-class children in Lima and poor children in Detroit were tested to assess the generality of the findings. Attendance at school was related to improvement in performance on all tasks. Improvement was equivalent for both locations, both cultural groups, and each social class. Attendance at school also was accompanied by reduced within-group variability on some tasks and by greater differentiation of cognitive processes within children. Location and cultural group interacted differentially by task according to a complex pattern of relations. There were no indications that the organization of memory or cognitive processes differed as a function of social class, age, location, or cultural group. The results were interpreted in terms of children's opportunities to acquire specific memory and cognitive skills from schooling and from their general experience in a particular environment.

Age Factors↗
PubMed1977

Attendance at a London casualty department.

Patients who attended the casualty department of the Middlesex Hospital during one week in 1973 were interviewed. A predominantly young and working population used the department. Relatively few patients lived close to the hospital but many worked nearby. One third of all attendances were by patients who had been asked to return by casualty doctors. About half the new patients came of their own accord; the next largest group had been sent directly from work by an employer or occupational health service. Half the patients came with injuries, many of them superficial, although there were also serious accident cases. One fifth of the patients had no general practitioner whom they could consult. Age and geographical mobility were related to whether or not patients were registered with a general practitioner. The main reasons for not consulting a general practitioner were that patients felt they needed hospital treatment or that it was more convenient to attend the casualty department. It is suggested that the view that casual attenders with relatively trivial complaints should be encouraged to go to a general practitioner is not always applicable since social as well as medical circumstances determine whether or not patients decide to visit casualty.

Emergency Service, Hospital↗
PubMed1976

The interaction between Beta-lactoglobulin and sodium N-dodecyl sulphate.

1. The binding of sodium n-dodecyl sulphate to beta-lactoglobulin was studied in the pH range 3.5-7.0 by equilibrium dialysis, ultracentrifugation and microcalorimetry. 2. At low binding concentrations (less than 30 bound surfactants anions per protein molecule) the complexes formed aggregates in solution. 3. At higher binding concentrations aggregation does not occur at low ionic strength (0.01 mol/litre), but continues at high ionic strength (0.1 mol/litre). 4. At 25 degrees C the enthalpy of interaction of sodium n-dodecyl sulphate with beta-lactoglobulin can be interpreted as the sum of the enthalpies of formation of a complex with 2 bound surfactant anions, with an enthalpy change of -9.5 kJ-mol-1 of bound surfactant, and complexes containing at least 22 bound surfactant anions, with limiting enthalpies per bound surfactant anion of -12.4 kJ-mol-1 at pH 3.5 and -3.25 kJ-mol-1 at pH 5.5. 5. The binding of surfactant and the enthalpy of interaction at pH 3.5 ARE NOT SIGNIFICANTLY AFFECTED BY THE ADDITION Of 8 M-urea. 6. The data indicate that at low binding concentrations the interaction is of an ionic nature, and is accompanied by a conformational change in the protein.

Calorimetry↗
PubMed1976

Automated adsorption isotherm device.

A device is described for the automated determination of the water adsorption isotherms of biological materials. The vapor pressure and weight of the adsorbate are measured directly with appropriate transducers, and equilibrium is defined on the basis of constant pressure. The accuracy of the device, determined on two samples with well-known water binding properties, is +/- 5%. Automation is achieved by electronic control.

Adsorption↗