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PubMed1985

A conductimetric method for assaying asparaginase activity in Aspergillus nidulans.

Aspergillus nidulans asparaginase activity may be assayed conductimetrically. The method is based on the increase of conductivity which is due to the production of ammonia and/or aspartate in a reaction mixture containing A. nidulans cell-free extract and asparagine or aspartate hydroxamate. This conductivity is linear with time and enzyme concentration and it follows Michaelis kinetics. Conductimetric activity was not detectable in mutants lacking asparaginase activity.

Asparaginase↗
PubMed1986

Direct measurements on individual microcapsule dissolution as a tool for determination of release mechanism.

A method is described for simultaneous microscopic observation of individual microcapsule core material dissolution together with quantitative measurement of the individual kinetics of release of the contents. These may be conductimetric in the case of ionized materials or spectrophotometric otherwise. This enables correlation of changes in core surface area during dissolution with kinetics. Surprisingly, both ethyl cellulose- and polymethacrylate-coated cores of potassium dichromate crystals, used as a model, showed localized internal dissolution universally, providing evidence of the exit of the salt via pores in the membrane, in spite of the kinetics being invariably zero order, as expected for individual microcapsules. The advantages of the method are presented.

Acrylic Resins↗
PubMed1994

Use of the Walden Product to evaluate the effect of amino acids on water structure.

The Walden Product, the product of viscosity (eta 0) and conductivity at infinite dilution of a solution (lambda 0), provides a measurement of the water-structuring activity of the solute. Measuring the effect of concentration on viscosity of solutions of amino acids, together with the conductivity of solutions of sodium chloride containing increasing concentrations of the amino acids, enabled Walden Products to be determined. The classical form of the Walden Product (lambda 0 eta 0) was used, together with a modified form, lambda 0 eta c, in which eta c was the slope of the concentration/viscosity curve. Most amino acids demonstrated modest water-structure-breaking activity but L-lysine, L-glutamic acid and L-aspartic acid, and their respective salts, all showed relatively higher activity. Dextrose behaved as a classical water-structure maker and, when added progressively, reversed the breaking activity of L-lysine. It is speculated that effects seen in bulk water may also occur at emulsion droplet surfaces, thereby inducing structural changes associated with the occasional rapid instability experienced when making admixtures of phospholipid-stabilized emulsions and additives such as amino acids and dextrose.

Amino Acids↗
PubMed1970

Growth in volume of Euglena gracilis during the division cycle.

The distribution of volumes of Euglena gracilis cells was measured conductimetrically. The volume spectrum of cultures in balanced growth was analyzed by the method of Collins and Richmond. The kinetics of volume increase of Euglena is neither linear nor exponential; the growth rate of small and large cells is low, but intermediate size cells show the largest growth rate.

Age Factors↗
PubMed1999

Modulation of distal colonic epithelial barrier function by dietary fibre in normal rats.

BACKGROUND: Dietary fibre influences the turnover and differentiation of the colonic epithelium, but its effects on barrier function are unknown. AIMS: To determine whether altering the type and amount of fibre in the diet affects paracellular permeability of intestinal epithelium, and to identify the mechanisms of action. METHODS: Rats were fed isoenergetic low fibre diets with or without supplements of wheat bran (10%) or methylcellulose (10%), for four weeks. Paracellular permeability was determined by measurement of conductance and 51Cr-EDTA flux across tissue mounted in Ussing chambers. Faecal short chain fatty acid (SCFA) concentrations were assessed by gas chromatography, epithelial kinetics stathmokinetically, and mucosal brush border hydrolase activities spectrophotometrically. RESULTS: Body weight was similar across the dietary groups. Conductance and 51Cr-EDTA flux were approximately 25% higher in animals fed no fibre, compared with those fed wheat bran or methylcellulose in the distal colon, but not in the caecum or jejunum. Histologically, there was no evidence of epithelial injury or erosion associated with any diet. The fibres exerted different spectra of effects on luminal SCFA concentrations and pH, and on mucosal indexes, but both bulked the faeces, were trophic to the epithelium, and stimulated expression of a marker of epithelial differentiation. CONCLUSIONS: Both a fermentable and a non-fermentable fibre reduce paracellular permeability specifically in the distal colon, possibly by promoting epithelial cell differentiation. The mechanisms by which the two fibres exert their effects are likely to be different.

Animals↗
PubMed1998

Calcium alginate dressings--I. Physico-chemical characterization and effect of sterilization.

In order to analyze the alginate components of alginate dressings and the fractions which are released when the dressing is in contact with model biological fluids, the use of various analytical methods was considered. The first step was the conversion of a calcium alginate batch to pure sodium alginate. The recovery of the latter from either insoluble or soluble mixed sodium/calcium alginates was performed by complexation of calcium ions with sodium citrate followed by ultrafiltration. Comparisons were made between sugar analysis, 1H NMR and circular dichroism (CD) data to determinate the contents in guluronic and mannuronic acids of sodium alginate chains. It was shown that CD measurements afford a rapid and nondestructive method for determination of %G when one takes the ratio theta200/theta220 into account. Fractionation of crude alginate (generally ranging from 30 to 70% G) was achieved by the triangle dissolution/precipitation method in order to increase the range of alginate in sugar composition. The various validated procedures were applied to investigate the effects of irradiation sterilization on alginate dressings. It was shown that sugar composition is retained whereas molecular weight decreased dramatically due to chain scission.

Alginates↗