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J D Robertson

Publications and source records attributed to J D Robertson.

At least 73 records · Page 4Linked to original sources
PubMed1982

On the structural organization of isolated bovine lens fiber junctions.

Junctions between fiber cells of bovine lenses have been isolated in milligram quantities, without using detergents or proteases. The structure of the isolated junctions has been studied by thin-section, negative-stain, and freeze-fracture electron microscopy and by x-ray diffraction. The junctions are large and most often have an undulating surface topology as determined by thin sectioning and freeze-fracture. These undulations resemble the tongue-and-groove interdigitations between lens fiber cells previously seen by others (D. H. Dickson and G. W. Crock, 1972, Invest. Ophthalmol. 11:809-815). In sections, the isolated junctions display a pentalamellar structure approximately 13-14 nm in overall thickness, which is significantly thinner than liver gap junctions. Each junctional membrane contains in the plane of the lipid bilayers distinct units arranged in a square lattice with a center-to-center spacing of 6.6 nm. Freeze-fracture replicas of the junctions fractured transversely show that the repeating units extend across the entire thickness of each membrane. Each unit is probably constructed from four identical subunits, with each subunit containing a protein of an apparent molecular weight of 27,000. We conclude that the lens junctions are structurally and chemically, different from gap junctions and could represent a new kind of intercellular contact, not simply another crystalline state of the gap junction protein.

Animals↗
PubMed1980

On the structure of the hemocyanin channel in lipid bilayers.

Keyhole limpet hemocyanin has been shown by others (Alvarez, O., Diaz, E. and Latorre, R. (1975) Biochim. Biophys. Acta 389, 444-448) to form single conductance channels in black lipid membranes. In an attempt to visualize how the large (300 A) water-soluble hemocyanin molecule interacts with lipid bilayers, we have examined hemocyanin in the presence of lipids with the electron microscope. We find that incubation of lipids with keyhole limpet hemocyanin produces a characteristic 70 A in diameter, ring-shaped particle or annulus associated with the bilayer. This annulus, which appears to be quite distinct from previously observed aggregated and dissociated forms of hemocyanin, may be responsible for the channel formation in black lipid membranes.

Animals↗
PubMed1980

On gap junction structure.

We have studied the stain distribution within rat liver gap junctions for specimens prepared by thin sectioning and negative staining. Pools of stain molecules exist in two specific locations with respect to the distinctive morphological units (connexons) of the junction. One pool of stain surrounds the connexons and is restricted to the extracellular space in the gap between the adjacent plasma membranes. The other pool of stain is located along in the central axis of each connexon, measures 1-2 nm in diameter and 4-5 nm in length, and is restricted to the gap region. On rare occasions, barely discernible linear densities seem to extend from this latter pool of stain and traverse the entire width of the junction. The data indicate the existence of a hydrophilic cavity along the central axis of te connexon which, in most instances, is restricted to the gap region. However, the precise depth to which this cavity may further extend along the connexon axis is still uncertain.

Animals↗
PubMed1980

Analysis of the structure of intramembrane particles of the mammalian urinary bladder.

The luminal and discoid vacuole membranes of the superficial cell layer of the transitional epithelium of the mammalian urinary bladder have been studied by thin-sectioning and freeze-fracture-etch (FFE) electron microscope methods. For the FFE studies membranes were deposited on a cationized glass surface, covered by a thin copper disc, and fractured under liquid N2. Specimens were etched at -100 degrees C and replicated at -190 degrees C. A model of the lattice membrane derived from thin sections was used to predict the heights of the fracture faces above the glass surface. A hexagonal pattern of globular intramembrane particles spaced 160 A apart was seen in the external fracture (EF) face plaques as previously described and regarded as the dominant structure. However, very extensive areas of another pattern, seen before in only limited areas, have beeen found in the EF faces. The pattern consists of a smooth hexagonal lattice with the same space constant as the globular one but a different structure. By image analysis it consists of overlapping domains bordered by shared but incomplete metal rims. Each domain has a central spot of metal encircled by a shadow. The surface of the smooth lattice is partly complementary to the corresponding protoplasmic fracture (PF) face which shows a similar hexagonal lattice with the same space constant. The height of the smooth EF lattice above the glass substrate is the same as the plane of the center of the lipid bilayer predicted by the model. The mean heights of the particles of the globular EF lattice are greater than the total thickness of the membrane as predicted by the model and confirmed by measurements. The globular EF lattice is not complementary and it is concluded that the globular particles do not exist in the native membrane but arise artifactually during the preparatory procedures.

Animals↗
PubMed1979

Interactions of Folch-Lees proteolipid apoprotein with planar lipid bilayers.

Water-soluble Folch-Lees proteolipid apoprotein from bovine CNS white matter induces a voltage-dependent conductance in black lipid membranes. Na+ is required for the induced conductance change but the established conductance has very low ionic selectivity. The induced conductance fluctuates with a minimum amplitude of 10(-11)--10(-10) mho. The magnitude of the conductivity change is dependent on protein concentration and on the composition of lipid bilayers. At a fixed voltage the induced conductance of a phosphatidylcholine-cholesterol membrane is proportional to the sixth power of the protein concentration and the first power of Na+ concentration. The interactions between the apoprotein and the lipids are both electrostatic and hydrophobic, but the interaction leading to the conductance increase appears to be mainly hydrophobic. Both the increase in conductance and the current fluctuations remain after extensive washing of the chambers to remove the protein. Furthermore, pronase or glutaraldehyde added to either the cis or trans side of the membrane does not affect the apoprotein-established conductance. However, if the bilayer is formed in the presence of both the apoprotein and pronase or if the apoprotein is treated with pronase prior to its addition to the chamber, no conductance change is observed. The association of the apoprotein with the membrane thus appears to render the protein inaccessible to proteolytic digestion, suggesting that the apoprotein is at least partially imbedded in the membrane interior.

Animals↗
PubMed1978

Structure of occluding junctions in ileal epithelial cells of suckling rats.

Two kinds of occluding junctions are found between ileal epithelial cells of suckling rats: apical zonulae occludentes (ZO) and fasciae occludentes (FO) which are associated with the lateral plasma membranes of many epithelial cells. In unfixed preparations, glycerol treatment induces the further proliferation of extensive fasciae occludentes. Both kinds of junction have identical structural elements when visualized in freeze fracture replicas, although the arrangement of these elements differs. Zonulae occludentes consist of networks of branching and anastomosing linear ridges or rows of approximately 10 nm particles with 20--30 nm spaces between the rows which form narrow belt-like structures around the apical region of adjacent cells. Fasciae occludentes, on the other hand, consist of similar linear ridges or rows of particles but the junction strands are often discontinuous, open ended and only occasionally intersect with each other. Several different fracture planes through the plasma membrane in the region of the occluding junctions have been observed and these provide further evidence that two components, one from each membrane, fused at the level of the extracellular space, form the junction sealing element. Furthermore, we present evidence which indicates a staggered rather than an in-register arrangement of these two components.

Animals↗
PubMed1977

The molecular organization of asymmetric lipid bilayers and lipid-peptide complexes.

Oriented fatty acid bilayers with asymmetric distributions of lipid head group types, hydrocarbon chain lengths, and associated polypeptides have been analyzed by a combined use of high resolution electron microscopy and X-ray diffraction techniques. The exclusion of fixatives, stains, and embedding materials has made it possible to relate unequivocally microscopic images to molecular composition. The ultrastructure of asymmetric bilayers has been determined by a novel analysis in which one half of the bilayer serves as a structural reference for the entire bilayer. Absolute electron density profiles at 7 A resolution have been computed for bilayers formed from long and short chain length lipids either segregated to opposite sides or mixed together in both sides of the bilayer. The data indicate that the two lipids self organize in a specific paired configuration. Detailed analysis of bilayers associated with poly-L-lysine shows that although this hydrophilic peptide resides near the lipid head group region, its presence alters the arrangement of the bilayer hydrocarbon chains.

Barium↗
PubMed1977

Banked autologous blood in total hip replacement.

Transfusion of banked autologous blood was used in 61 patients requiring a total hip replacement. Up to 3 units of blood may be removed by phlebotomy within three weeks of the operation. Hemoglobin levels of less than 7 milligrams and hematocrit levels below 29 had no adverse effect on wound healing or resistance to infection. Autologous transfusion avoids many of the problems associated with homologous blood transfusion, especially serum hepatitis.

Arthritis, Rheumatoid↗
PubMed1976

Images of divalent cations in unstained symmetric and asymmetric lipid bilayers.

Divalent cations have been microscopiccally visualized in association with simple lipid bilayers. Symmetric and asymmetric oriented bilayers were constructed from fatty acid monolayers and were cut in thin transverse sections for examination by bright field electron microscopy in the absence of stains, fixatives or embedding materials. It has been found that bilayers formed of lipid molecules having alkaline earth head groups exhibit natural electron contrast. The intrinsic image has been liked to local variations in the bilayer absolute electron density profile determined by X-ray diffraction analysis of the same specimens (McIntosh, T. J., Waldbillig, R. C. and Robertson, J. D. (1976) Biochim. Biophys. Acta 448, 15-33). By combining the microscopic, chemical and X-ray evidence it has been estimated that local increments of about 1 g/cm3 can produce detectable elelcron contrast in 500 A transverse sections of bilayers.

Barium↗
PubMed1976

Lipid bilayer ultrastructure. Electron density profiles and chain tilt angles as determined by X-ray diffraction.

High resolution (6A) electron density profiles have been computed on an absolute electron density scale for bilayers composed of both saturated fatty acids and fatty acids associated with the alkaline earth series of divalent cations. Lowangle X-ray diffraction data have been interpreted by an isomorphous replacement technique. The position on the X-ray film of discrete wide-angle reflections has provided direct information on the hydrocarbon chain packing and chain tilt in these bilayers. These results have been correlated to an electron microscopy study of the same bilayers (Waldbilling, R. C., Robertson, J.D. and McIntosh, T. J. (1976) Biochim. Biophys. Acta 448, 1-14) and also to X-ray diffraction studies of fatty acid crystals. A method for forming and structurally analyzing bilayers of well defined chemical asymmetry is also described.

Barium↗
PubMed1976

Regular structures in unit membranes. III. Further observations on the particulate component of the suckling rat ileum endocytic membrane complex.

Further morphological observations on the particulate components decorating the lumenal surfaces of membranes of the endocytic complex of the epithelial cells of the suckling rat ileum are presented. The particles each measure approximately 7.5 nm across and give the appearance of the capital letter H in frontal view. They consist of the enzyme n-acetyl-beta-glucosaminidase (NAG). They are arranged in rows called "decorated strips" with the symmetrical lateral bars in register and spaced approximately 14.5 nm apart. Decorated strips lie side-by-side in the external (lumenal) surface of the membrane. They are parallel and sometimes spaced approximately 14.5 nm apart making an orthogonal lattice. The lateral spacing between the decorated strips under certain conditions is reduced and sometimes there is shear between the adjacent ones. Occasionally, shear is present within the decorated strips themselves, with slight displacement of the two sides of each H-shaped particle. A purified preparation of these membranes has been studied by electron microscopy using thin sectioning, negative stain, Markham translation and optical diffraction computer image reconstruction methods. The individual particles comprising the array can be seen in the membrane surface in profile view when dried in a pool of negative stain. They appear either triangular or diamond-shaped in such views. If triangular, they appear to consist of three domains at the corners of an equilateral triangle. One side of each triangular figure is parallel to the membrane surface but separated from it by a dense band of negative stain approximately 2 nm thick that runs along the surface of the membrane. Sometimes a fourth symmetrical domain is visible within this dense band, giving a diamond-shaped figure. This fourth domain connects the particle to the membrane. Thus, each H-shaped particle is a double structure, with each half in profile view appearing as a diamond figure of four symmetrical domains. Each H-shaped particle is believed to consist of either two or four molecules of NAG.

Animals↗