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M Duckworth

Publications and source records attributed to M Duckworth.

28 records · Page 2Linked to original sources
PubMed1972

The location of N-acetylgalactosamine in the walls of Bacillus subtilis 168.

The N-acetylgalactosamine in the walls of Bacillus subtilis 168 occurs in two polymers. One of these contains N-acetylgalactosamine, glucose and phosphorus and is attached to the peptidoglycan through an alkali-labile bond; preliminary studies indicate that a repeating unit of this polymer is glucosyl-N-acetylgalactosamine 1-phosphate. N-Acetylgalactosamine is also associated with the peptidoglycan in a component that is not converted into the free sugar or other soluble compounds on treatment of the walls with alkali. The two polymers containing N-acetylgalactosamine are released on autolysis of the walls and can be separated by ion-exchange chromatography. As glucose 6-phosphate is produced by gentle hydrolysis of the wall with acid a third phosphate polymer, poly(glucose 1-phosphate), may occur in this wall. However, as no polymer with this structure could be separated from that containing galactosamine, its existence has not been established unequivocally. The methods described permit the study of variations in N-acetylgalactosamine content with respect to growth conditions.

Bacillus subtilis↗
PubMed1969

An extracellular agarase from a Cytophaga species.

1. An extracellular enzyme has been isolated from cultures of the bacterium growing on agar or porphyran. 2. Partial purification of the enzyme has been achieved by precipitation with ammonium sulphate followed by gel filtration on DEAE-Sephadex A-50. 3. The optimum conditions for the enzyme acting on porphyran are pH7.2 and a temperature of 40-41 degrees . 4. The enzyme has an endoaction, producing a rapid decrease in viscosity of agar or porphyran solutions with little development of reducing power. 5. From the action of the enzyme on various polysaccharides, it is concluded that the enzyme is specific for the agarose structure.

Agar↗
PubMed1969

The action of a bacterial agarase on agarose, porphyran and alkali-treated porphyran.

1. A purified extracellular agarase from a Cytophaga species was used to hydrolyse agarose, porphyran and alkali-treated porphyran. 2. The hydrolysate from agarose was separated by gel filtration into the series of neoagarosaccharides, the predominant member of which was the tetrasaccharide. 3. Enzyme action on alkali-treated porphyran gave neoagarosaccharides and other oligosaccharides containing 6-O-methyl-d-galactose units. From the composition of these oligosaccharides it is deduced that action of the enzyme on a d-galactosidic linkage is four to five times faster than on the 6-O-methyl-d-galactosidic linkage. 4. Enzyme action on native porphyran gives a similar series of oligosaccharides but in smaller yield, much of the polysaccharide being either not degraded or only degraded to a series of large, highly sulphated oligosaccharides. 5. For porphyran, it is concluded that 6-O-methyl ether groups are distributed randomly on half the d-galactose units, but that the 6-sulphate groups on l-galactose units tend to occur in blocks.

Chromatography, Gel↗
PubMed1969

The specificity of an agarase from a Cytophaga species.

1. The extracellular agarase from a Cytophaga species was shown to have no action on neoagarobiose, neoagarotetraose or their analogues containing 6-O-methyl-d-galactose residues. 2. The action of the enzyme on neoagaro-octaose suggests that scission of the central beta-d-galactosidic linkage, to form two molecules of tetrasaccharide, is the preferred mode of action; however, both exterior d-galactosidic linkages in the octasaccharide and both in neoagarohexaose are hydrolysed at a somewhat lower rate. 3. Sulphated oligosaccharides produced by prolonged enzyme action on porphyran have a minimum degree of polymerization of about 8-10units. 4. For such sulphated oligosaccharides to be further hydrolysed by enzyme action, it is suggested that an unmodified neoagarotetraose residue must be present in the oligosaccharide. 6. A new method for determining the degree of polymerization of these large oligosaccharides is described.

Chromatography, Ion Exchange↗
PubMedDate not supplied

Assessing the assessments: a comparison of two clinical pragmatic profiles.

Recent years have seen a growth in interest in pragmatic aspects of communication, and the application of this area to language disorders. This has led to the development of a range of "pragmatic profiles" to assess the disordered language of children and adults. In this study we investigate two such profiles designed for use with aphasic patients. In particular we look at aspects of interscorer reliability (comparing scorers from different linguistic traditions), scoring sensitivity (two- versus five-point scales), and diagnostic accuracy (the ability to differentiate different aphasic syndromes). We conclude that training in scoring these profiles must be uniform, but also that greater sensitivity is needed in the categories available.

Aged↗