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Biomedical subjects

V J Morris

Publications and source records attributed to V J Morris.

50 records · Page 3Linked to original sources
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↗
PubMed1990

Multinuclear n.m.r. studies of group I cations in furcellaran gels.

Multinuclear n.m.r. experiments were carried out in order to study the possible selective interaction between group I cations and furcellaran. It has been shown that the intensity of the 39K, 87Rb and 133Cs spectra show a change in the vicinity of the sol-gel transition. However, the intensity of the 23Na spectrum showed no singularity at the sol-gel transition. These studies suggest that the selective interactions of the group I cations upon gelation of furcellaran resemble those observed for the structurally related kappa-carrageenan.

Alginates↗
PubMed1990

Light scattering studies of tetramethyl ammonium gellan.

Tetramethyl ammonium (TMA) gellan does not gel. Light scattering studies suggest that in solutions of TMA gellan, in tetramethyl ammonium chloride (TMACI), the gellan molecules assemble end to end to produce elongated fibrous structures. Such fibrils are envisaged as resulting from double-helix formation between the ends of neighbouring gellan molecules. Fibrils with molecular weights ranging from (1.06 +/- 0.06) x 10(5) to (4.5 +/- 0.1) x 10(6) have been observed. The molecular weights obtained depended upon the pore size of the filters used to clarify the solutions. The formation of strong gels, in the presence of gel promoting cations, is attributed to a localized ordered lateral association, or crystallization of regions of these fibrils. It is suggested that such a model for gelation may be of general applicability to a number of polysaccharide systems.

Crystallization↗
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

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↗
PubMed1986

Structure of the extracellular gelling polysaccharide produced by Enterobacter (NCIB 11870) species.

The gelling polysaccharide produced by a species of Enterobacter (NCIB 11870) contains L-fucose, D-glucose, and D-glucuronic acid in the ratios 1:2:1. Analysis of the methylated and methylated, carboxyl-reduced polysaccharide revealed terminal non-reducing glucose, (1----3)-linked fucose, (1----3,1----4)-linked glucose, and (1----4)-linked glucuronic acid in the ratios 1:1:1.2:0.8. From the results of Smith degradation of the polysaccharide and spectroscopic studies of the acidic tetra- and octa-saccharides produced by bacteriophage-induced enzymic depolymerization of the polysaccharide, the following tetrasaccharide repeating-unit is proposed. (Formula: see text). This repeating-unit is identical to that of the capsular polysaccharide produced by Klebsiella aerogenes serotype K54 except for the absence of O-acetyl groups. The effects of the O-acetyl groups on the secondary structure and rheological properties of these polysaccharides are discussed.

Carbohydrate Conformation↗
PubMed1977

The effect of antibiotics on the electrical polarisability of aqueous suspensions of bacteria.

The orientation of washed Escherichia coli bacteria in suspension induced by applied a.c. electric fields has been monitored by observing the accompanying changes in the intensity of light scattered by the suspension. The data enable the anisotropy of electrical polarisability deltaalpha to be determined. Changes in deltaalpha due to the addition of various antibiotics to the suspension have been measured as a function of both the antibiotic concentration and the temperature of the suspension. The results are taken to indicate that there is an accumulation of the antibiotic molecules at the bacterial surface.

Adsorption↗
PubMed1976

An electro-optic study of the effect of certain aminoglycoside antibiotics on the electrical polarizability of sensitive, dependent and resistant strains of Escherichia coli.

A study has been made of the effect of certain aminoglycoside antibiotics on the electrical properties of the surfaces of one sensitive, two resistant and one dependent form of E. coli K-12. The method employed was to observe the change in scattered light produced when the bacteria in suspension are orientated by an applied a. c. electric field. The effect of the antibiotics has been analysed in terms of drug accumulation at the bacterial surface. Differences have been noted in the responses of the sensitive form to different aminoglycosides and an attempt has been made to correlate these differences with mimimum inhibitory concentrations. Differences have also been noted in the response of certain resistant and dependent forms of E. coli to streptomycin.

Anti-Bacterial Agents↗
PubMed1975

The effect of neomycin and streptomycin on the electrical polarisability of aqueous suspensions of Escherichia coli.

Aqueous suspensions of bacteria scatter light strongly. In addition, the bacteria exhibit strong induced dipole moments in an electric field. In this note we report how, by measuring the intensity of the scattered light, the electric polarisability (alpha) of Escherichia coli could be monitored as small quantities of antibiotics were added to the suspensions. The effect of the presence of quite small quantities of antibiotic on the electrical polarisability, which gave rise to the induced dipole, was dramatic. From the hypothesis that alpha had its origins in the bacteria-solvent interface, a theory is presented which adequately accounts for both alpha and its changes in the presence of these antibiotics. The study is taken to suggest that the antibiotic molecules were adsorbed on to the bacterial surface thereby reducing the surface charge. This in turn reduces the number of counterions and the apparent induced dipole moment. Because the electric-field scattering method is both quick and sensitive to changes in alpha, it may prove a valuable method for the study of antibiotic action on cell and microorganism surfaces.

Escherichia coli↗
PubMed1975

Infrared scattering: a method for evaluating the mass and size of bacteria.

In the realm of biophysics and biochemistry, light scattering is used extensively to evaluate the molecular weight and size of macromolecules and particles in suspension. Bacteria scatter strongly but are too large for the conventional procedures. By extending the wavelength lambda of the incident radiation into the infrared, we show that the effective size of the bacteria (relative to lambda) is reduced, and the usual Zimm plot measurements and procedure can be applied to evaluate the molecular weight and size. Details of the apparatus, its alignment, calibration and use are given along with data for aqueous suspensions of the three species Serratia marcescens, Escherichia coli and Thiobacillus ferrooxidans. The method has the advantages of being suitable for rod-like or ellipsoid-like bacteria as well as spheres, for polydisperse samples and for monitoring the effects of environment, antibodies and chemical therapeutic agents on the bacteria.

Escherichia coli↗