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Biomedical subjects

D C Watts

Publications and source records attributed to D C Watts.

At least 145 records · Page 8Linked to original sources
PubMed1981

Human erythrocyte acetylcholinesterase in relation to cell age.

Acetylcholinesterase was studied in human red cells that had been fractionated on Ficoll/Triosil density gradients into classes representing different ages in vivo. Reticulocytes have negligible acetylcholinesterase activity; this is rapidly acquired on maturation to the erythrocyte. The activity per cell reaches a maximum and then, after a constant period, declines again towards the end of cell life. The maximum activity and the rates of activity gain and loss per cell are quantitatively different in adults and children. Kinetic studies showed that Vmax. follows the same age/activity profile but Km is unaffected by cell age. The acetylcholinesterase protein content, determined by quantitative crossed immunoelectrophoresis, also shows a profile of increase and then decrease with cell age but the specific activity calculated from the protein estimate shows a reverse picture in which there is a slight decrease from young to mid-age cells followed by an increase again in older cells. These results are interpreted to indicate a complex developmental picture in which the overall cell age against enzyme activity profile is determined partly by the amount of enzyme protein present and partly from the modifying effect on the enzyme activity, of interactions with an aging cell membrane.

Acetylcholinesterase↗
PubMed1981

The rheological properties of polyelectrolyte cements. I. polycarboxylates.

The rheological behaviour of six setting carboxylate cements was studied by capillary techniques in the shear rate of 0.65-65 s-1 and the cements were found to behave as power law fluids. All cements became dilatant as setting progressed and the kinetics of apparent viscosity increase, were found to follow an exponential function of time, exp (mt), with m congruent to 0.5.

Acrylic Resins↗
PubMed1981

The rheological properties of polyelectrolyte cements II. Glass ionomers.

The rheological properties of two glass ionomer cements, ASPA and Fuji have been investigated. The viscosities of the liquid components of these systems have been found to be Newtonian up to a shear rate of 140 s-1 with values of 0.80 N m-2 s for ASPA and 1.8 N m-2 for Fuji. Capillary viscometry techniques have been employed to study the rheological changes accompanying setting. Both cements appear to behave as power law fluids, becoming progressively dilatant as setting proceeds. The apparent viscosities of the two systems are approximately equivalent displaying values of the order of 50 N m-2 s, at a shear rate of unity shortly after mixing.

Chemical Phenomena↗
PubMed1981

Glycolytic, pentose-phosphate shunt and transaminase enzymes in gastrocnemius muscle, liver, heart, and brain of two mouse mutants, 129 J-dy and A2g-adr, with abnormal muscle function.

Aldolase and phosphoglycerate kinase activity were markedly reduced in muscle from two mouse mutants, 129 J-dy and A2G-adr, with abnormal muscle development. The pentose-phosphate shunt enzymes, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, were both greatly increased in the gastrocnemius of 129 J-dy mice, but only the former was slightly increased in A2G-adr muscle. Alanine and aspartate aminotransferase activities were normal or low in 129 J-dy muscle but increased to approximately 200% in A2G-adr muscle. Liver from 129 J-dy mice showed increased activity of glucose-6-phosphate dehydrogenase. These findings are compatible with the well-recognised lipid involvement in the 129 J-dy mutant but indicate that an abnormality of amino acid metabolism in relation to energy supply is probably more important in the A2G-adr mutant.

Animals↗
PubMed1981

Thermal diffusivity in finite cylindrical specimens of dental cements.

1. A method has been developed and described for obtaining accurate thermal diffusivity values for dental cements and other restorative materials. This method employs specimens of a short cylindrical geometry which are readily fabricated from simply-constructed molds. 2. Results obtained for polycarboxylate and glass-ionomer cements show that the diffusivity values are mainly in the range of 2-3 x 10-3 cm2 s-1. Thus, the thermal characteristics of these materials are suitable if the cements are used as insulating bases below amalgam restorations. 3. thermal diffusivity values are a potential tool for investigating structure/property relationships in restorative materials, being sensitive to moisture content, powder/liquid ratio, and other compositional variables.

Dental Cements↗
PubMed1981

Specific spectrophotometric assay for the M isoenzymes of pyruvate kinase in plasma samples containing mixtures of the muscle (M) and liver (L) isoenzymes.

Plasma pyruvate kinase (EC 2.7.1.40) activity contains two major isoenzymes. The "L" type originates from liver (erythrocytes contain a similar isoenzyme), the "M" type predominantly from skeletal muscle. The diagnostic use of pyruvate kinase as an index of muscle leakage requires an assay of only the M type. An M-type-selective assay for mixtures of the two isoenzymes was devised, based on the differences that the L form has a higher Km for phosphoenolpyruvate and is inhibited by about 95% by a high concentration of ADP. All relevant conditions of the assay have been examined and the reaction system has been optimized at 30 degrees C. The assay yields the expected Km values for M type pyruvate kinase. An apparent increase in activity in hemolysed plasma samples was found to be derived from leukocytes.

Blood Specimen Collection↗
PubMed1980

Changes in some cytoplasmic enzymes from red cells fractionated into age groups by centrifugation in Ficoll/Triosil gradients. Comparison of normal humans and patients with Duchenne muscular dystrophy.

1. A procedure is described for the fractionation into age classes of human red cells on a Ficoll/Triosil discontinuous density gradient. The fractionated cells appear minimally affected by the procedure. 2. Individual blood samples show a normal cell distribution, but the mean cell density may vary slightly. To allow for this in comparing samples, cell ages are expressed in terms of the mean and standard deviations from the mean. 3. Reticulocyte number decays exponentially in the gradient. By back extrapolation, a standard deviation can be computed corresponding to the theoretical age at which the sample contains 100% reticulocytes. This value can be used to calculate the theoretical activity of an enzyme in the reticulocytes and the enzyme half-life. 4. Glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and glutathione reductase activities in unfractionated and age-fractionated cells were investigated in adults, children and patients with Duchenne muscular dystrophy. 5. The half-life for adult glucose 6-phosphate dehydrogenase (48 days) compares with that found by other workers. In children the half-life is 24 days, although the initial activity is essentially unaltered. 6. The half-life of 6-phosphogluconate dehydrogenase was found to be 117 days; the activity of glutathione reductase did not alter throughout the life of the cell. There was no difference between adults and children for these enzymes. The same results were obtained with dystrophic patients as for control children for all three enzymes.

Adolescent↗
PubMed1980

The use of arginine analogues for investigating the functional organization of the arginine-binding site in lobster muscle arginine kinase. Role of the 'essential' thiol group.

1. The nature of arginine binding to lobster arginine kinase and the extent of its possible involvement with the ;essential' thiol group of the enzyme has been investigated with some inhibitory analogues of arginine. 2. Most of the analogues inhibit competitively, although mixed inhibition may occur if the alpha-carboxy group or alpha-amino group is absent. 3. The K(i) values indicate that strength of binding depends on the length of the carbon chain (l-isoleucine>l-valine>l- alpha-aminobutyrate>l-alanine) and the integrity of the substituents on the alpha-carbon atom (l-arginine>agmatine and l-ornithine>putrescine). The guanidino group probably contributes little to substrate binding, but a positive charge near the delta-nitrogen atom appears to be important (l-ornithine>l -citrulline>l-alpha-aminobutyrate). A cyclic analogue, 2-carboxymethyl-3-oxo-2,3,5,6,7,8-hexahydro-1H-imidazo [1,2-a][1,3]diazepine-8-carboxylic acid, has a low K(i) value similar to that of an equivalent straight-chain form, suggesting that arginine probably binds in a folded configuration. 4. The aliphatic l-amino acids give enzyme difference spectra similar to that with l-arginine and the integrity of the alpha-carboxy and alpha-amino groups appears to be a minimal but not sufficient requirement for this, as l-ornithine gives an atypical difference spectrum. A difference spectrum is interpreted as indicating an enzyme conformational change. No difference spectrum was observed with methylguanidine. 5. The ability of aliphatic alpha-l-amino acids to protect against inhibition by 5,5'-dithiobis-(2-nitrobenzoic acid) is proportional to the number of atoms in the carbon chain and inversely proportional to K(i). Ornithine gives greater protection than citrulline; analogues lacking the alpha-amino groups also protect. Agmatine, lacking the alpha-carboxy group, did not protect. 6. It is concluded that it is unlikely that the ;essential' thiol group in the enzyme interacts with any part of the arginine molecule during catalysis except, possibly, the alpha-carboxyl group.

Animals↗