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Biomedical subjects

D Branton

Publications and source records attributed to D Branton.

At least 109 records · Page 6Linked to original sources
PubMed1977

Interpreting the results of freeze-etching.

Morphological data obtained by freeze-fracturing and other low temperature techniques must be interpreted in terms of molecular organization and function. Interpretation is aided by physical and biochemical approaches. Physical approaches such as rotary replication and ultralow temperature fracturing can improve resolution and preserve molecular arrangements which are difficult or impossible to observe with standard freeze-etching techniques. Biochemical approaches such as dissociation-reconstitution experiments can establish the molecular parameters underlying electron-microscopically visible forms. Both approaches are illustrated by investigations of the human erythrocyte membrane.

Erythrocyte Membrane↗
PubMed1977

Intramembrane particle aggregation in erythrocyte membranes and band 3-lipid recombinants.

The low pH-induced aggregation of intramembrane particles in human erythrocyte membranes was studied in native membranes and in a reconstituted model system. A significant difference in such aggregation was found when samples of freshly prepared ghosts were compared to ghosts receiving pretreatments that removed most of spectrin-actin from underneath the membrane. All conditions effective in aggregating particles are equally effective in precipitating extracted mixtures of spectrin and actin. In Band 3-lipid recombinants, the pH-induced aggregation of particles was duplicated only in samples containing spectrin-actin that equilibrated with these recombinants in sucrose gradients. Therefore, it was proposed that spectrin-actin components, through their associations with the underlying intramembrane particles, could impede particle lateral mobility and also determine particle redistribution in erythrocyte membrane.

Actins↗
PubMed1976

Intramembrane particle aggregation in erythrocyte ghosts. II. The influence of spectrin aggregation.

Physicochemical properties of mixtures of spectrin and actin extracted from human erythrocyte ghosts have been correlated with ultrastructural changes observed in freeze-fractured erythrocyte membranes. (1) Extracted mixtures of spectrin and actin have a very low solubility (less than 30 mug/ml) near their isoelectric point, pH 4.8. These mixtures are also precipitated by low concentrations of Ca2+, Mg2+, polylysine or basic proteins. (2) All conditions which precipitate extracts of spectrin and actin also induce aggregation of the intramembrane particles in spectrin-depleted erythrocyte ghosts. Precipitation of the residual spectrin molecules into small patches on the cytoplasmic surface of the ghost membrane is thought to be the cause of particle aggregations, implying an association between the spectrin molecules and the intramembrane particles. (3) When fresh ghosts are exposed to conditions which precipitate extracts of spectrin and actin, only limited particle aggregation occurs. Instead, the contraction of the intact spectrin meshwork induced by the precipitation conditions compresses the lipid bilayer of the membrane, causing it to bleb off particle-free, protein-free vesicles. (4) The absence of protein in these lipid vesicles implies that all the proteins of the erythrocyte membrane are immobilized by association with either the spectrin meshwork or the intramembrane particles.

Actins↗
PubMed1976

Reconstitution of intramembrane particles in recombinants of erythrocyte protein band 3 and lipid: effects of spectrin-actin association.

The integral membrane protein Band 3 of the human erythrocyte, either purified or in a crude Triton X-100 extract of ghosts, was combined with egg lecithin in a cholate solution. During dialysis to remove cholate, lipid bilayer vesicles formed in which Band 3 existed as a dimer and in which intramembrane particles indistinguishable from those in the native membrane were exposed by freeze-fracturing. The recombinant vesicles were stable in both high and low salt concentrations, sedimented at a density that increased in prportion to their protein content, and bound spectrin-actin extracted from erythrocyte ghosts. When spectrin-actin was associated with the vesicles, the behavior of the recombinant intramembrane particles simulated that of the erythrocyte ghost intramembrane particles: they were dispersed at pH 7.6 and aggregrated at pH 5-5.5. Thus, some of the characteristics of the native membrane have been reconstituted in the recombinant.

Actins↗
PubMed1976

Freeze-fracture autoradiography: feasibility.

We have shown that the combination of freeze-fracture with electron microscope autoradiography can be developed into a technique for correlating the molecular structure of the biological membrane with its chemical and functional characteristics. Within the limits of electron microscope autoradiographic resolution, FARG has the potential to detect the relative distribution of molecules in each half of the membrane and within the plane of the membrane. The use of radioisotopic labels in combination with freezing techniques requires minimal perturbation of the system being studied and may be suitable for the examination of substances which would be extracted or would diffuse during the normal fixation and embedding procedures used in standard electron microscope autoradiography.

Autoradiography↗
PubMed1974

Intramembrane particle aggregation in erythrocyte ghosts. I. The effects of protein removal.

We have used freeze-etching and SDS-polyacrylamide gel electrophoresis to study the conditions under which the intramembrane particles of the human erythrocyte ghost may be aggregated. The fibrous membrane protein, spectrin, can be almost entirely removed from erythrocyte ghosts with little or no change in the distribution of the particles. However, after spectrin depletion, particle aggregation in the plane of the membrane may be induced by conditions which cause little aggregation in freshly prepared ghosts. This suggests that the spectrin molecules form a molecular meshwork which limits the translational mobility of the erythrocyte membrane particles.

Blood Proteins↗
PubMed1972

Control of daughter-cell number variation in multiple fission: genetic versus environmental determinants in Prototheca.

Prototheca zopfii has been developed as an experimental system for studying the control of cytokinesis and daughter-cell number variation in multiple fission. Although mean daughter-cell number increases linearly with growth rate, and this dependency is genetically controlled, pedigree analysis shows that daughter-cell number variation is not under direct genetic control. In a population growing in steady-state balanced growth, each cell has a given probability of dividing into 2, 4, 8 16, or 32 daughter-cells. These probabilities are independent of the division number of the cell in the preceding generation, and can be altered by changes in the culture medium.

Cell Count↗