A Tetragonal Lattice in Mammalian Lens Junctions
A pure fraction of junctional membranes has been isolated in milligram quantities from bovine lens without detergents. SDS-PAGE analysis shows a major band at 27,000 d and a minor one at 21,000 d. Thin section electron microscopy (EM) of this fraction revealed junctions of two closely apposed membranes with an overall thickness of 135-140 Å with a wavy contour and lengths greater than 10 μm. Negative stain and freeze-fracture (FF) EM (only unetched specimens so far) and X-ray diffraction studies of unfixed and unglycerinated specimens were in agreement regarding the structure of the junctions. They consisted primarily of extensive domains of sub-units arranged in a 66 Å tetragonal lattice. Specimens were spun down centrifugally in a Beem capsule and partially dried for the x-ray diffraction studies. The X-ray patterns contained several reflections which indexed on a tetragonal lattice of 66 Å in the equatorial direction parallel to the plane of the membranes and several bands of a continuous transform in the meridional direction consistent with membrane pairs. No diffraction was seen at 85 Å in the equatorial direction.