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Biomedical subjects

R Josephs

Publications and source records attributed to R Josephs.

At least 55 records · Page 3Linked to original sources
PubMed1977

Structural study of spectrin from human erythrocyte membranes.

Human erythrocyte spectrin prepared from fresh blood is a mixture of different association states. Depending on the manner of preparation, the two-chain dimer or the tetramer predominates. These forms are not in rapid thermodynamic equilibrium. The molecular weight of the dimer by sedimentation and diffusion and by light scattering is about 5 X 10(5). The frictional properties indicate a low or moderate asymmetry (axial ratio in the range 2-10), and from the angular dependence of light scattering intensity an upper limit of about 80 A can be set for the radius of gyration. The tetramer similarly has a moderate asymmetry. Electron microscopy reveals that the dimer is a compact, slightly elongated molecule, and that the tetramer probably consists of two parallel dimers. On increasing the concentration of solutions containing spectrin dimers, oligomers are formed, which are not rapidly dissociated on dilution. At very low protein concentrations (below about 0.05 mg/mL) there is evidence of the onset of a rapid dissociation equilibrium between dimers and single chains. Other physical properties of the spectrin have been measured. The size and shape of the spectrin molecule would seem to rule out any major physical resemblance to myosin.

Erythrocyte Membrane↗
PubMed1976

Organization of intramembrane particles in freeze-cleaved gap junctions of rat graafian rollicles: optical-diffraction analysis.

Gap junctions were identified in the membrana granulosa and cumulus oophorus, and between cells of the internal theca, of the preovulatory rat follicle. In replicas of freeze fractured follicles, the A face presented clusters of closely packed intramembrane particles, 7--9 nm in diameter, forming a mosaic pattern, while the B face showed a similar pattern of small pits. Optical diffraction analysis of these electron micrographs revealed that both the intramembrane particles and the corresponding pits were organized in hexagonal lattices with centre-to-centre spacing of 9-10 nm. In small junctions (up to 0.4 mum in diameter), both A and B faces generally consisted of a single lattice, while large junctions (0.5-2 mum) contained multiple lattices differing in orientation. Occasionally intramembrane particles and pits were more loosely arranged throughout the junctional area and failed to show a hexagonal pattern. Both granulosa and thecal cells often contained intracellular vesicles resembling annular junctions. These contained intramembrane particles whose assembly resembled that of the gap junctions with regard to periodicity and lattice organization. Examination of thin section of thin sections suggested that small gap junctions occur also between cytoplasmic processes of coronal cells and the oolemma. No tight junctions were detected between granulosa cells and between thecal cells.

Animals↗