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Biomedical subjects

G F Elliott

Publications and source records attributed to G F Elliott.

At least 37 records · Page 2Linked to original sources
PubMed1988

Bovine corneal stroma contains a structural glycoprotein located in the gap region of the collagen fibrils.

Treatment of bovine corneal stroma using SDS-containing extracting solutions removes a 135,000 MW glycoprotein from the main collagen framework of the tissue. Low-angle synchrotron X-ray diffraction patterns obtained from corneas extracted in this way indicate that the glycoprotein has been removed from the gap regions of the collagen fibrils and is thus an important structural component of the corneal stroma. The glycoprotein (GP 135) shares a number of properties with one of the subunits of type VI collagen, but tests have so far failed to establish their identity.

Amino Acids↗
PubMed1987

Diffuse X-ray scatter from myosin heads in oriented synthetic filaments.

X-ray results are presented concerning the structural state of myosin heads of synthetic filaments in threads. These were made from purified rabbit skeletal muscle myosin and studied by x-ray diffraction and electron microscopy by Cooke et al. (Cooke, P. H., E. M. Bartels, G. F. Elliott, and R. A. Hughes, 1987, Biophys. J., 51:947-957). X-ray patterns show a meridional peak at a spacing of 14.4 nm. We concentrate here on the only other feature of the axial pattern: this is a central region of diffuse scatter, which we find to be similar to that obtained from myosin heads in solution (Mendelson, R. A., K. M. Kretzschmar, 1980, Biochemistry, 19:4103-4108). This means that the myosin heads have very large random displacements in all directions from their average positions, and that they are practically randomly oriented. The myosin heads do not contribute to the 14.4-nm peak, which must come entirely from the backbone. Comparison with x-ray data from the unstriated Taenia coli muscle of the guinea pig indicates that in this muscle at least 75% of the diffuse scatter comes from disordered myosin heads. The results confirm that the diffuse scatter in x-ray patterns from specimens that contain myosin filaments can yield information about the structural behavior of the myosin heads.

Actin Cytoskeleton↗
PubMed1987

The organisation of collagen fibrils in the human corneal stroma: a synchrotron X-ray diffraction study.

The low angle equatorial diffraction pattern from the human corneal stroma shows that the collagen fibrils have two preferred orientations: inferior-superior and medial-lateral. We have not observed this effect in any other animal species. This arrangement, which was found to be more pronounced in the posterior than in the anterior stroma, was maintained until the last 1 to 2 millimetres before the limbus at which point uniaxial orientation was observed along the circumference. Our interpretation of this result is that most collagen fibrils wrap around the circumference of the cornea and relatively few continue radially into the limbus where uniformity of collagen fibril diameters is lost.

Aged↗
PubMed1986

A synchrotron X-ray diffraction study of bovine cornea stained with cupromeronic blue.

Bovine corneal stroma was stained with the dye Cupromeronic Blue under "critical electrolyte" conditions in order to locate the proteoglycans specifically. Electron microscopy revealed that most of the stained proteoglycan filaments are randomly distributed in the tissue although there are many regions where a close proteoglycan-collagen relationship is evident. On counterstaining the collagen in order to identify the intra-periodic banding pattern, the proteoglycan filaments were seen to predominate at three axial positions within the collagen D-period corresponding to electron-optical staining bands a, c and d/e. X-ray diffraction patterns were obtained from the stained and unstained corneae using a high intensity synchrotron source. Integrated intensities from the meridional patterns were used to calculate a difference electron density distribution which revealed where the collagen was axially modified by the stain. This distribution indicated the presence of the dye periodically associated with the collagen at three major sites, one adjacent to each gap/overlap junction (at electron-optical staining bands a and c) and one in the gap zone (including staining bands d and e). However, the Cupromeronic Blue treatment is estimated to have contributed only about 12% to the variation in electron density along the collagen. The staining also gave rise to a greatly increased level of diffuse background scatter, which, in agreement with the electron-optical observations, indicates that much of the stained material is not ordered with respect to the collagen but is randomly distributed in the tissue.

Animals↗
PubMed1985

Donnan potentials in rabbit psoas muscle in rigor.

Collins and Edwards (1971, Am. J. Physiol., 221:1130-1133) have shown that a tissue potential can be measured with microelectrodes in glycerinated muscle and that this potential is consistent with a Donnan equilibrium of small ions due to the concentration of net fixed electric charge on the contractile proteins. This approach has been combined with x-ray and light diffraction measurements of the muscle lattice dimensions, and the data are used to determine the thick filament charge and thin filament charge under a variety of different conditions. The thick filament charge is a function of the bathing solution, in particular its pH and ionic composition. These parameters are important in determining the volume of the equilibrium lattice and possibly are involved in the contraction mechanism itself.

Animals↗
PubMed1985

Donnan potentials from the A- and I-bands of glycerinated and chemically skinned muscles, relaxed and in rigor.

Using a combination of microelectrode measurements and high-power microscopy we have demonstrated that different Donnan potentials can be recorded from the A- and I-bands of glycerinated and chemically skinned muscles in rigor, so that the A-band fixed charge concentration exceeds the I-band fixed charge concentration in the rigor condition. In relaxation the two potentials, and therefore the two charge concentrations, are equal in the two bands. X-ray data are presented for relaxed and rigor rat semitendinosus muscle, chemically skinned, and actin and myosin filament charges are calculated under a variety of conditions. Our conclusions are that (a) the fixed (protein) charge is different in the A- and I-bands of striated muscle in the rigor state; (b) the fixed charges are equal in the A- and I-bands of relaxed muscle; (c) the largest charge change between relaxation and rigor is on the thick filament. This occurs whether or not the myosin heads are cross-linked to the thin filaments. (d) Possibly an event on the myosin molecule, the binding of ATP (or certain other ligands) causes a disseminated change that modifies the ion-binding capacity of the myosin rods, or part of them.

Animals↗
PubMed1982

Donnan potential measurements in extended hexagonal polyelectrolyte gels such as muscle.

In this paper we reconsider the theoretical and practical aspects of using KCl-filled microelectrodes in extended polyelectrolyte gels such as muscle to measure Donnan potentials, and then calculate protein fixed-charge concentrations. An analytical calculation of the electrical potential function between muscle filaments shows that whether the microelectrode averages the ionic concentration or the local potentials the results are indistinguishable in the practical regime. After consideration of this and other possible sources of error, we conclude that the charge-concentrations measurements that have appeared in the literature are legitimate.

Animals↗
PubMed1981

The distribution of electron density in corneal collagen fibrils.

Using high intensity synchrotron X-ray diffraction data, an electron density profile has been obtained for the collagen fibrils in corneal stroma at higher resolution than has been possible before. The details within this electron density distribution are discussed in terms of the collagen and its interactions with other components present in the tissue.

Collagen↗
PubMed1980

Swelling studies of bovine corneal stroma without bounding membranes.

1. The swelling characteristics of demembranated bovine corneal stroma were studied as a function of time and of the pH and ionic strength of the bathing solution. 2. Compared with other pH values, the stroma swelled least near pH 4. 3. In the pH range 6--10, increasing the pH resulted in an increase both in the rate of swelling and in the hydration reached in a given time. 4. At pH 2 and 4, a final constant value of hydration was attained. At higher pH values no such equilibrium was attained when the hydration of the tissue was followed for at least 100 hr. 5. The swelling at high pH values was consistent with the hypothesis that the Donnan-osmotic contribution is the major component of the swelling pressure. 6. The ionic strength dependence was complex. There was a general decrease of swelling with increase in the ionic strength (mu) until around mu = 0.1. The swelling at mu = 0.15 was greater than at mu = 0.1 and mu = 0.25. 7. The results were interpreted on the assumption that the Donnan-osmotic effect is the major component of the swelling pressure.

Animals↗