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Biomedical subjects

M J Miles

Publications and source records attributed to M J Miles.

29 records · Page 2Linked to original sources
PubMed1992

Visualization of the algal polysaccharide carrageenan by scanning tunnelling microscopy.

Scanning tunnelling microscopy has been used to obtain images in the constant-current mode in air and moist conditions at molecular resolution for the kappa- and iota-carrageenan algal polysaccharides. The molecules were deposited from an aqueous solution onto a graphite substrate. The samples formed aligned nematic-like arrays and were also found as individual molecules. The molecular dimensions of width, height and repeat distance along the molecule were found to be close to the values previously determined by X-ray diffraction. The results support a molecular model based on a double-helix structure for carrageenan.

Carbohydrate Sequence↗
PubMed1992

Molecular images of cereal proteins by STM.

Scanning tunnelling microscopy (STM) has been used to study a seed storage protein of wheat known as gamma-gliadin. The protein was deposited onto highly oriented pyrolytic graphite (HOPG) from solutions of trifluoroethanol (TFE) and 1% acetic acid. Samples were dried down and then scanned in air. Transmission electron microscopy (TEM) was also used to visualise the distribution of protein on the substrate. Small-angle X-ray scattering (SAXS) was used to compare the molecular size and shape obtained with those from the STM images.

Gliadin↗
PubMed1991

Scanning tunneling microscopy of a wheat seed storage protein reveals details of an unusual supersecondary structure.

Scanning tunneling microscopy has been used to demonstrate that a spiral structure based on beta-reverse turns is adopted by the repeat sequences present in a group of wheat gluten proteins. This structure is similar to the beta-spiral formed by a synthetic polypentapeptide based on a repeat sequence present in elastin. Wheat gluten and elastin are both elastomeric and it is possible that the spiral structure contributes to this property.

Journal Article↗
PubMed1991

Molecular transforms of kappa carrageenan and furcellaran from mixed gel systems.

X-ray fibre diffraction studies of furcellaran-carob, furcellaran-tara, and furcellaran-konjac mannan mixed gels have failed to reveal any evidence for the predicted intermolecular binding between the algal polysaccharide helix and the galactomannan or glucomannan (konjac) mannan). In the absence of such interactions, mixed gels of kappa carrageenan-konjac mannan and furcellaran-konjac mannan, have been used to obtain good quality molecular transforms of the kappa carrageenan and furcellaran molecules in an oriented nematic liquid crystalline form. Analyses of the pattern support double helix structures with threefold symmetry with helix pitch of 2.5 nm. The absence of a 0.83 nm meridional in kappa carrageenan necessitates zero axial translation from the exact half-stagger position, contrary to the model building prediction. An axial translation from half-stagger is necessary for furcellaran.

Alginates↗
PubMed1989

Molecular origins of acetan solution properties.

Acetan is a branched acidic heteropolysaccharide secreted by Acetobacter xylinum. X-ray diffraction studies of oriented fibres suggest non-crystalline helices with fivefold symmetry and a pitch of 4.8 nm. Optical rotation and circular dichroism studies are consistent with the retention of the helical structure in solution and a helix-coil transition upon heating and cooling. Aqueous solutions yield high 'low shear rate' viscosity and shear-thin upon shearing.

Acetobacter↗
PubMed1989

Aqueous dissolution of crystalline and amorphous amylose-alcohol complexes.

Complexes of amylose, the linear starch polysaccharide, with linear alcohols having chain lengths varying from 4 to 8 carbon atoms, were prepared. Either crystalline or amorphous complexes could be formed depending on preparation conditions. Crystalline complexes gave sharp X-ray diffraction patterns, characteristic of the VH form of amylose, whereas no observable pattern was obtained from the amorphous form. Thermal dissociation of the complexes occurred at increasing temperatures with increasing alcohol chain length. Crystalline complexes dissociated at temperatures approximately 23 degrees C higher than their amorphous counterparts and the enthalpy of dissociation was also greater for the crystalline samples. Enthalpy values were independent of alcohol chain length. Differences in thermal behaviour of the two types of complex may be described in terms of the polymer crystal lattice energy and may explain the variability of reported results for complex dissociation in the literature.

Alcohols↗
PubMed1989

Structure of the globular protein vicilin revealed by scanning tunnelling microscopy.

Scanning tunnelling microscopy (s.t.m.) has been used to study the structure of the non-crystalline globular protein vicilin. Molecules were deposited on amorphous carbon substrates and imaged both in air and in vacuo without additional sample preparation. Current-voltage plots of an individual protein molecule are also reported. The s.t.m. images are compared with conventional transmission electron micrographs and with a model of vicilin based on small-angle synchrotron X-ray scattering data.

Electric Conductivity↗
PubMed1989

Naturally-evolved changes in bacterial polysaccharides.

Major roles suggested for extracellular polysaccharides are as antigens, 'phage receptor sites or for protecting cells against dehydration. The evolution of bacterial species has led to a large number of bacterial polysaccharides with complex chemical repeat units. There is growing evidence that such structures may be grouped into families of polymers differing in only small changes in chemical structure. Physico-chemical studies of such families are starting to reveal which variations are important in changing the functional properties of the polymers.

Biological Evolution↗