On the structural organization of isolated bovine lens fiber junctions.

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Abstract
Junctions between fiber cells of bovine lenses were isolated in milligram quantities without using detergents or proteases. The structure of the isolated junctions was 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 observed (Dickson and Crock, 1972). In sections, the isolated junctions display a pentalamellar structure .apprx. 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 4 identical subunits, with each subunit containing a protein of an apparent MW of 27,000. Apparently, 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.