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Biomedical subjects

W M Ledingham

Publications and source records attributed to W M Ledingham.

16 recordsLinked to original sources
PubMed2005

Screening of chitin deacetylase from Mucoralean strains (Zygomycetes) and its relationship to cell growth rate.

Chitin deacetylase (CDA) is an enzyme that catalyzes the hydrolysis of acetamine groups of N-acetyl-D: -glucosamine in chitin, converting it to chitosan in fungal cell walls. In the present study, the activity in batch culture of CDA from six Mucoralean strains, two of them wild type, isolated from dung of herbivores of Northeast Brazil, was screened. Among the strains tested, Cunninghamella bertholletiae IFM 46114 showed a high intracellular enzyme activity of 0.075 U/mg protein after 5 days of culture, and a wild-type strain of Mucor circinelloides showed a high intracellular enzyme activity of 0.060 U/mg protein, with only 2 days of culture, using N-acetylchitopentaose as substrate. This enzyme showed optimal activity at pH 4.5 in 25 mM glutamate-sodium buffer at 50 degrees C, and was stable over 1 h preincubation at the same temperature. The kinetic parameters of CDA did not follow Michaelis-Menten kinetics, but rather Hill affinity distribution, showing probable allosteric behavior. The apparent K(HILL) and Vmax of CDA were 288+/-34 nmol/l and 0.08+/-0.01 U mg protein(-1) min(-1), respectively, using N-acetylchitopentaose as substrate at pH 4.5 at 50 degrees C.

Amidohydrolases↗
PubMed2003

Chitosan from Syncephalastrum racemosum used as a film support for lipase immobilization.

Chitosan from a native Mucoralean strain, Syncephalastrum racemosum, isolated from herbivorous dung (Northeast-Brazil), was used as a film support for lipase immobilization. S. racemosum showed highest chitosan yield (152 mg g dry mycelia weight(-1); 15.2% of dry mycelia weight) among the nine strains screened, which presented 89% D-glucosamine. A chitosan film was used for lipase (EC 3.1.1.3) immobilization using glutaraldehyde as a bifunctional agent. The immobilized lipase retained 47% (12.6 micromol s(-1) m(-2)) of its initial catalytic activity after four cycles of reaction. This result is comparable (same order of magnitude) to that of the enzyme immobilized on film made from commercially available crustacean chitosan.

Animals↗
PubMed2001

Effect of culture conditions on lipase production by Fusarium solani in batch fermentation.

Lipase (Glycerol ester hydrolase EC 3.1.1.3.) from a Brazilian strain of Fusarium solani FSI has been investigated. The effect of different carbon sources and trace elements added to basal medium was observed with the aim of improving enzyme production. Lipase specific activity was highest (0.45 U mg(-1)) for sesame oil. When this medium was supplemented with trace elements using olive oil, corn oil and sesame oil the lipase specific activity increased to 0.86, 1.89 and 1.64 U mg(-1), respectively, after 96 h cultivation without any considerable biomass increase. The Km of this lipase using pNPP (p-nitrophenylpalmitate) as substrate, was 1.8 mM with a Vmax of 1.7 micromol min(-1) mg protein(-1). Lipase activity increased in the presence of increasing concentrations of hexane and toluene. In contrast, incubation of this enzyme with water-soluble solvents decreased its activity after 10% concentration (v/v) of the solvent. The lipase activity was stable below 35 degrees C but above this temperature activity losses were observed.

Bioreactors↗
PubMed1994

Lipase from a Brazilian strain of Penicillium citrinum.

A lipases (glycerol ester hydrolases E. C. 3.1.1.3) from a brazilian strain of Penicillium citrinum has been investigated. When the microorganism was cultured in the simple medium (1.0% olive oil and 0.5% yeast extract), using olive oil in as carbon source in the inocula, the enzyme extracted showed maximum activity (409 IU/mL). In addition, decrease of yeast extract concentration also reduces the lipase activity. Nevertheless, when yeast extract was replaced by ammonium sulfate, no activity was detected. Purification by precipitation with ammonium sulfate showed best activity in the 40-60% fraction. The optimum temperature for enzyme activity was found in the range of 34-37 degrees C. However, after 30 min at 60 degrees C, the enzyme was completely inactivated. The enzyme showed optimum at pH 8.0. The dried concentrated fraction (after dialysis and lyophilization) maintained its lipase activity at room temperature (28 degrees C) for 8 mo. This result in lipase stability suggests an application of lipases from P. citrinum in detergents and other products that require a high stability at room temperature.

Brazil↗
PubMed1992

Effects of potassium on the ethanol production rate of Saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation.

The influence of potassium on ethanol production by Saccharomyces cerevisiae wild type and AR5 cells carrying the plasmid pCYG4 was investigated. This plasmid carries the glutamate dehydrogenase gene conferring an 11-fold higher level of expressed enzyme activity over the wild type cells. All experiments were carried out in batch culture with medium supplemented to different potassium concentrations up to 180 mM. Maximum ethanol production rate was observed in the AR5 cells grown in medium supplemented with 3.5 mM of potassium ions. Glucose uptake rate increased with increasing potassium up to 60 mM, but higher concentrations depressed glucose uptake rate in both strains. Furthermore, the wild type cells showed higher growth rate, ethanol production, and glucose consumption rate than the AR5 cells. These lower rates in the AR5 cells could be explained by repression of potassium uptake by an enhancement of ammonium feeding, and greater energy requirements by these cells due the presence of the plasmid.

Ammonia↗
PubMed1992

Uptake of ammonia by Saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation.

Batch culture experiments involving ammonia uptake in Saccharomyces cerevisiae BC55 pCYG4 have been carried out. This strain carries the plasmid pCYG4 that directs substantial overproduction of NADP-GDH, conferring an 11-fold increase in activity. The wild type cells had a specific growth rate greater than BC55 pCYG4. The ammonia uptake was practically the same until 15 h of growth. However, the amount of ammonia hydroxide added during growth (60 h) was two and half times greater in the BC55 pCYG4 than wild type cells. The results suggest that the presence of the plasmid pCYG4 can increase the amount of ammonia taken by the cells, but not the amount of biomass.

Ammonia↗
PubMed1991

On immediate functional bracing of Colles' fracture.

A prospective randomized trial was carried out in 60 consecutive patients with Colles' fractures requiring manipulation. They were treated by either a standard Colles' plaster (control group) or in a functional plaster brace applied immediately after reduction of the fracture. The brace extended from the proximal radius and ulna to the level of the radial styloid and allowed a full range of movement at the radiocarpal joint. Both groups comprised 30 patients and were matched for age, sex and dominance of hand. There was no significant difference in initial severity of fracture or the quality of reduction. Radiological results on cast removal (35-42 days) were significantly better in the brace group compared with those treated with a below-elbow cast (P less than 0.05). Wrist function was also significantly better in the brace treated group at 12 weeks after fracture (P less than 0.05). This brace has a number of advantages over standard plaster treatment, but requires a degree of skill and experience in its application. A prefabricated brace has now been developed with a similar 'built in' three-point loading which will be easier for inexperienced staff to apply.

Adult↗
PubMed1991

Radiographic assessment of splinting bandages.

The physical attenuation of X-rays by a variety of splinting bandages was measured and compared with the subjective opinion of nine radiologists. The radiolucency of the bandages and their interference with the interpretation of bony detail on radiographs (using a radiographic knee phantom) was assessed. Plaster-of-Paris (POP) bandages produced the greatest attenuation of X-rays and the greatest interference with interpretation of bony detail. All the polyurethane resin impregnated fabric bandages produced less attenuation than POP, but variations occurred due to the fabric type and knit of the bandage. The lowest attenuation occurred in those bandages using cotton, polyester or polypropylene fabric, and in all but one instance these caused least interference in radiographic interpretation. The exception was the polyester bandage, where the coarse knit of the fabric produced a large difference in X-ray beam absorption between the air spaces and the bandage. The distracting mesh pattern on the radiograph interfered with radiographic visualization. The glass fibre bandages caused intermediate attenuation, being better than POP but not as radiolucent as the non-glass fabrics.

Bandages↗
PubMed1991

Modern splinting bandages.

We have assessed the current range of synthetic splinting bandages, using physical and mechanical tests and the subjective opinions of patients, volunteers and orthopaedic staff. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive, and potentially more hazardous.

Bandages↗
PubMed1990

Studies on Saccharomyces cerevisiae under carbon-limiting growth transformed with plasmid pCYG4 that carries the gene for NADP-GDH.

The gene (GDH1) coding for the NADP-linked glutamate dehydrogenase system (NADP-GDH) has been cloned from Saccharomyces cerevisiae strain. Cells being transformed by the NADP-GDH gene on a 2 micron bared vector (pCYG4) plasmid confering 11-fold higher level on expressed GDH activity over the wild-type cells. The behavior of these cells was investigated under chemostatic growth with a carbon rate-limiting nutrient. Specific growth rates of cells carrying plasmid pCYG4 were found to be slightly slower than wild type cells. Furthermore, the NADP-GDH activity increases proportionally with the dilution rate. In addition, oscillations in the NADP-GDH activity, especially at a dilution rate up to 0.15/h, are probably consequential on the appearance of a changing mixed population (cells with and without plasmids).

Carbon↗
PubMed1988

Studies on Saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation. Batch experiments.

Batch culture experiments of three different strains of Saccharomyces cerevisiae have been carried out. The first strain was transformed by a plasmid pCYG4, which carries the glutamate dehydrogenase (NADP-GDH, E.C. 1.4.14) gene conferring an 11-fold increase in activity. The second was transformed by the same plasmid, but without NADP-GDH, and the third was the wild type. The specific growth rates of the two recombinant DNA strains were below that of the wild type, which can be related to extra plasmid protein production.

Ammonia↗
PubMed1987

Mechanical assessment of polyurethane impregnated fibreglass bandages for splinting.

The introduction of polyurethane (PU) resin impregnated fibreglass bandages is likely to have a significant effect on modern orthopaedic practice. The manufacturers of these products claim many improved properties compared to plaster of Paris bandages, such as , high strength to weight ratio, rapid setting time and high radiolucency. This paper reports on a series of mechanical tests designed to assess the strength, flexibility, working time and wear properties of the current range of fibreglass bandages and to compare them with plaster of Paris bandages. The results have clearly demonstrated that the fibreglass bandages are mechanically superior and offer numerous advantages over plaster of Paris for use as the definitive casting material for both weight-bearing and non-weight-bearing casts.

Bandages↗
PubMedDate not supplied

Ammonia assimilation in S. cerevisiae under chemostatic growth.

Glutamate, glutamine, and ammonia pool size have been determined in two S. cerevisiae strains (GOGAT+ and GOGAT-) growing under ammonia excess and limitation at a dilution rate of 0.10/h. The biomass levels and glutamate dehydrogenase NADPH-dependent (NADPH-GDH) activities were also measured for both strains. The strain that lacks GOGAT activity showed lower levels of metabolites under both media and lower levels of biomass under carbon limitation (ammonia excess) compared to the GOGAT+ strain. Under nitrogen limitation, the biomass level was the same for both strains, but GOGAT- changed from rounded to ellipsoidal cells.

Ammonia↗