Biomedical subjects

S S Sikerwar

Publications and source records attributed to S S Sikerwar.

5 recordsLinked to original sources

PubMed1991

Three-dimensional structure of an invertebrate intercellular communicating junction.

Gap junctions containing extensive, highly ordered crystalline arrays of hexagonally packed connexons have been isolated from the hepatopancreas of the arthropod, Homarus americanus (American lobster). The structure of such junctions has been studied to a resolution of approximately 25 A in three dimensions by electron microscopy of negatively stained specimens. The structure, which has the crystallographic symmetry of the two-sided plane group p6, reveals the connexon as an annular oligomer which projects approximately 30-45 A from the cytoplasmic surface. The stain-filled channel structure appears to be approximately 40-45 A wide in the extracellular region. Projection images of glucose-embedded specimens extend to a resolution of 10 A, and show a strong contrast from the connexon subunits. Overall the structure is quite similar to that of rat liver junctions, except that less stain is seen in the aqueous region of the gap and more surrounding the protrusions of the protein into the cytoplasm.

Animals↗

PubMed1988

Three-dimensional structure of gap junctions in fragmented plasma membranes from rat liver.

Gap junctions forming extensive hexagonal crystalline sheets (unit cell dimension, a = 89 A) were obtained by mild mechanical disruption of plasma membranes from rat liver. The sheets were analysed in three dimensions by negative stain electron microscopy and Fourier image processing. The crystallographic symmetry was shown to approximate to the two-sided plane group p622, indicating that the sheets are composed of two equivalent, oppositely-facing membrane assemblies. The structure of the connexon in these near-to-native junctions is essentially the same as that found in detergent-extracted junctions, the subunits appearing slightly tilted tangential to the central six-fold axis and aligned almost perpendicular to the membrane plane.

Animals↗

PubMed1983

A structural characterization of gap junctions isolated from mouse liver.

Mouse liver gap junctions have been isolated by using an anionic detergent, n-dodecanoyl sarcosine, in combination with non-ionic polyoxyethylene ethers (Brij 35 and Brij 58) and (W-1) detergents. Purified gap junctions are obtained in a sucrose step gradient containing 1-o-n-octyl-beta-D-glucopyranoside. This procedure is aimed at minimizing proteolysis. The junctions thus isolated have a hexagonal lattice of connexons with a lattice constant of 7.6-8.4 nm. Presence of a major Mr 26,000 gap junctional protein has been confirmed by SDS-PAGE.

Animals↗

PubMed1981

Subunit structure of the connexons in hepatocyte gap junctions.

The connexons in the mouse hepatocyte gap junctions consistently reveal a subunit structure in rotary shadowed replicas of quick frozen freeze-fractured material. Quick freezing eliminates treatment of the material with chemical fixatives and cryoprotectants and hence captures the structures in their native state. Previous biophysical studies have indicated that the connexon in hepatocyte gap junction is composed of 6 subunits. In rotary shadowed replicas, some connexons have 6 subunits while the rest reveal less than 6 subunits. Visualization of less than 6 subunits may be due to local variations in the angle of shadowing because of an uneven plane of fracturing and/or breaking of some of the subunits during freeze-fracturing. Markham's rotation technique reveals that some connexons have a hexameric symmetry while others approach a tetrameric symmetry. Using models of connexons and tilting experiments with the replicas it is shown that these apparent deviations from the hexameric symmetry result from inclination of the fractured face relative to the plane of viewing.

Animals↗

PubMed1979

Visualization of mitochondrial coupling factor F1(ATPase) by freeze-drying.

It is known that the negatively stained preparations of inner mitochondrial membrane display characteristic approximately 9 nm F1 (ATPase) knobs projecting from the matrix surface. Freeze-etch studies have reported the absence of such knobs from the "etched" surface of the inner mitochondrial membranes. We have demonstrated their presence on the surface of SMP (submitochondrial particles) prepared by freeze-drying for transmission electron microscopy. This identification has been substantiated by comparison with freeze-dried TU particles (trypsin-urea treated SMP) that are devoid of F1 (ATPase). It has been suggested that a layer of water molecules is strongly adsorbed to the surface of SMP and does not sublime during normal freeze-"etching."

Adenosine Triphosphatases↗