On the structural organization of isolated bovine lens fiber junctions.

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.